thodg/libgit2

diff --git a/include/git2/errors.h b/include/git2/errors.h
index 085dd52..5a4e540 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -103,7 +103,7 @@ typedef enum {
 	GIT_EOBJCORRUPTED = -28,
 
 	/** The given short oid is ambiguous */
-	GIT_EAMBIGUOUSOIDPREFIX = -29,
+	GIT_EAMBIGUOUS = -29,
 
 	/** Skip and passthrough the given ODB backend */
 	GIT_EPASSTHROUGH = -30,
@@ -128,11 +128,13 @@ typedef enum {
 	GITERR_REPOSITORY,
 	GITERR_CONFIG,
 	GITERR_REGEX,
+	GITERR_ODB
 } git_error_class;
 
 /**
  * Return a detailed error string with the latest error
  * that occurred in the library.
+ * @deprecated This will be replaced in the new error handling
  * @return a string explaining the error
  */
 GIT_EXTERN(const char *) git_lasterror(void);
@@ -144,6 +146,7 @@ GIT_EXTERN(const char *) git_lasterror(void);
  * NOTE: This method will be eventually deprecated in favor
  * of the new `git_lasterror`.
  *
+ * @deprecated This will be replaced in the new error handling
  * @param num The error code to explain
  * @return a string explaining the error code
  */
@@ -151,9 +154,23 @@ GIT_EXTERN(const char *) git_strerror(int num);
 
 /**
  * Clear the latest library error
+ * @deprecated This will be replaced in the new error handling
  */
 GIT_EXTERN(void) git_clearerror(void);
 
+/**
+ * Return the last `git_error` object that was generated for the
+ * current thread or NULL if no error has occurred.
+ *
+ * @return A git_error object.
+ */
+GIT_EXTERN(const git_error *) git_error_last(void);
+
+/**
+ * Clear the last library error that occurred for this thread.
+ */
+GIT_EXTERN(void) git_error_clear(void);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/attr.c b/src/attr.c
index 0aa1e32..a0d6f29 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -317,13 +317,12 @@ static int collect_attr_files(
 	const char *workdir = git_repository_workdir(repo);
 	attr_walk_up_info info;
 
-	if ((error = git_attr_cache__init(repo)) < GIT_SUCCESS)
-		goto cleanup;
-
-	if ((error = git_vector_init(files, 4, NULL)) < GIT_SUCCESS)
-		goto cleanup;
+	if (git_attr_cache__init(repo) < 0 ||
+		git_vector_init(files, 4, NULL) < 0)
+		return -1;
 
-	if ((error = git_path_find_dir(&dir, path, workdir)) < GIT_SUCCESS)
+	error = git_path_find_dir(&dir, path, workdir);
+	if (error < 0)
 		goto cleanup;
 
 	/* in precendence order highest to lowest:
@@ -334,13 +333,13 @@ static int collect_attr_files(
 	 */
 
 	error = push_attrs(repo, files, repo->path_repository, GIT_ATTR_FILE_INREPO);
-	if (error < GIT_SUCCESS)
+	if (error < 0)
 		goto cleanup;
 
 	info.repo = repo;
 	info.files = files;
 	error = git_path_walk_up(&dir, workdir, push_one_attr, &info);
-	if (error < GIT_SUCCESS)
+	if (error < 0)
 		goto cleanup;
 
 	if ((error = git_repository_config(&cfg, repo)) == GIT_SUCCESS) {
@@ -352,19 +351,17 @@ static int collect_attr_files(
 		git_config_free(cfg);
 	}
 
-	if (error == GIT_SUCCESS) {
+	if (!error) {
 		error = git_futils_find_system_file(&dir, GIT_ATTR_FILE_SYSTEM);
-		if (error == GIT_SUCCESS)
+		if (!error)
 			error = push_attrs(repo, files, NULL, dir.ptr);
 		else if (error == GIT_ENOTFOUND)
-			error = GIT_SUCCESS;
+			error = 0;
 	}
 
  cleanup:
-	if (error < GIT_SUCCESS) {
-		git__rethrow(error, "Could not get attributes for '%s'", path);
+	if (error < 0)
 		git_vector_free(files);
-	}
 	git_buf_free(&dir);
 
 	return error;
@@ -373,32 +370,29 @@ static int collect_attr_files(
 
 int git_attr_cache__init(git_repository *repo)
 {
-	int error = GIT_SUCCESS;
 	git_attr_cache *cache = &repo->attrcache;
 
 	if (cache->initialized)
-		return GIT_SUCCESS;
+		return 0;
 
 	if (cache->files == NULL) {
 		cache->files = git_hashtable_alloc(
 			8, git_hash__strhash_cb, git_hash__strcmp_cb);
 		if (!cache->files)
-			return git__throw(GIT_ENOMEM, "Could not initialize attribute cache");
+			return -1;
 	}
 
 	if (cache->macros == NULL) {
 		cache->macros = git_hashtable_alloc(
 			8, git_hash__strhash_cb, git_hash__strcmp_cb);
 		if (!cache->macros)
-			return git__throw(GIT_ENOMEM, "Could not initialize attribute cache");
+			return -1;
 	}
 
 	cache->initialized = 1;
 
 	/* insert default macros */
-	error = git_attr_add_macro(repo, "binary", "-diff -crlf");
-
-	return error;
+	return git_attr_add_macro(repo, "binary", "-diff -crlf");
 }
 
 void git_attr_cache_flush(
@@ -432,8 +426,9 @@ void git_attr_cache_flush(
 
 int git_attr_cache__insert_macro(git_repository *repo, git_attr_rule *macro)
 {
+	/* TODO: generate warning log if (macro->assigns.length == 0) */
 	if (macro->assigns.length == 0)
-		return git__throw(GIT_EMISSINGOBJDATA, "git attribute macro with no values");
+		return 0;
 
 	return git_hashtable_insert(
 		repo->attrcache.macros, macro->match.pattern, macro);
diff --git a/src/attr_file.c b/src/attr_file.c
index 0299343..35679ef 100644
--- a/src/attr_file.c
+++ b/src/attr_file.c
@@ -180,37 +180,37 @@ int git_attr_file__lookup_one(
 		}
 	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
-int git_attr_fnmatch__match(
+bool git_attr_fnmatch__match(
 	git_attr_fnmatch *match,
 	const git_attr_path *path)
 {
-	int matched = FNM_NOMATCH;
+	int fnm;
 
 	if (match->flags & GIT_ATTR_FNMATCH_DIRECTORY && !path->is_dir)
-		return matched;
+		return false;
 
 	if (match->flags & GIT_ATTR_FNMATCH_FULLPATH)
-		matched = p_fnmatch(match->pattern, path->path, FNM_PATHNAME);
+		fnm = p_fnmatch(match->pattern, path->path, FNM_PATHNAME);
 	else if (path->is_dir)
-		matched = p_fnmatch(match->pattern, path->basename, FNM_LEADING_DIR);
+		fnm = p_fnmatch(match->pattern, path->basename, FNM_LEADING_DIR);
 	else
-		matched = p_fnmatch(match->pattern, path->basename, 0);
+		fnm = p_fnmatch(match->pattern, path->basename, 0);
 
-	return matched;
+	return (fnm == FNM_NOMATCH) ? false : true;
 }
 
-int git_attr_rule__match(
+bool git_attr_rule__match(
 	git_attr_rule *rule,
 	const git_attr_path *path)
 {
-	int matched = git_attr_fnmatch__match(&rule->match, path);
+	bool matched = git_attr_fnmatch__match(&rule->match, path);
 
 	if (rule->match.flags & GIT_ATTR_FNMATCH_NEGATIVE)
-		matched = (matched == GIT_SUCCESS) ? FNM_NOMATCH : GIT_SUCCESS;
+		matched = !matched;
 
 	return matched;
 }
diff --git a/src/attr_file.h b/src/attr_file.h
index 1ba18f9..6284c53 100644
--- a/src/attr_file.h
+++ b/src/attr_file.h
@@ -82,7 +82,7 @@ extern int git_attr_file__lookup_one(
 /* loop over rules in file from bottom to top */
 #define git_attr_file__foreach_matching_rule(file, path, iter, rule)	\
 	git_vector_rforeach(&(file)->rules, (iter), (rule)) \
-		if (git_attr_rule__match((rule), (path)) == GIT_SUCCESS)
+		if (git_attr_rule__match((rule), (path)))
 
 extern unsigned long git_attr_file__name_hash(const char *name);
 
@@ -96,13 +96,13 @@ extern int git_attr_fnmatch__parse(
 	const char *source,
 	const char **base);
 
-extern int git_attr_fnmatch__match(
+extern bool git_attr_fnmatch__match(
 	git_attr_fnmatch *rule,
 	const git_attr_path *path);
 
 extern void git_attr_rule__free(git_attr_rule *rule);
 
-extern int git_attr_rule__match(
+extern bool git_attr_rule__match(
 	git_attr_rule *rule,
 	const git_attr_path *path);
 
diff --git a/src/blob.c b/src/blob.c
index b67f8af..20dcece 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -42,7 +42,7 @@ int git_blob__parse(git_blob *blob, git_odb_object *odb_obj)
 	assert(blob);
 	git_cached_obj_incref((git_cached_obj *)odb_obj);
 	blob->odb_object = odb_obj;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int git_blob_create_frombuffer(git_oid *oid, git_repository *repo, const void *buffer, size_t len)
@@ -51,58 +51,50 @@ int git_blob_create_frombuffer(git_oid *oid, git_repository *repo, const void *b
 	git_odb *odb;
 	git_odb_stream *stream;
 
-	error = git_repository_odb__weakptr(&odb, repo);
-	if (error < GIT_SUCCESS)
+	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0 ||
+		(error = git_odb_open_wstream(&stream, odb, len, GIT_OBJ_BLOB)) < 0)
 		return error;
 
-	if ((error = git_odb_open_wstream(&stream, odb, len, GIT_OBJ_BLOB)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to create blob");
+	if ((error = stream->write(stream, buffer, len)) == 0)
+		error = stream->finalize_write(oid, stream);
 
-	if ((error = stream->write(stream, buffer, len)) < GIT_SUCCESS) {
-		stream->free(stream);
-		return error;
-	}
-
-	error = stream->finalize_write(oid, stream);
 	stream->free(stream);
-
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to create blob");
-
-	return GIT_SUCCESS;
+	return error;
 }
 
-static int write_file_stream(git_oid *oid, git_odb *odb, const char *path, git_off_t file_size)
+static int write_file_stream(
+	git_oid *oid, git_odb *odb, const char *path, git_off_t file_size)
 {
 	int fd, error;
 	char buffer[4096];
 	git_odb_stream *stream = NULL;
 
-	if ((error = git_odb_open_wstream(&stream, odb, file_size, GIT_OBJ_BLOB)) < GIT_SUCCESS)
+	if ((error = git_odb_open_wstream(
+			&stream, odb, (size_t)file_size, GIT_OBJ_BLOB)) < 0)
 		return error;
 
-	if ((fd = p_open(path, O_RDONLY)) < 0) {
-		error = git__throw(GIT_ENOTFOUND, "Failed to create blob. Could not open '%s'", path);
-		goto cleanup;
+	if ((fd = git_futils_open_ro(path)) < 0) {
+		stream->free(stream);
+		return -1;
 	}
 
-	while (file_size > 0) {
+	while (!error && file_size > 0) {
 		ssize_t read_len = p_read(fd, buffer, sizeof(buffer));
 
 		if (read_len < 0) {
-			error = git__throw(GIT_EOSERR, "Failed to create blob. Can't read full file");
-			p_close(fd);
-			goto cleanup;
+			giterr_set(
+				GITERR_OS, "Failed to create blob. Can't read whole file");
+			error = -1;
 		}
-
-		stream->write(stream, buffer, read_len);
-		file_size -= read_len;
+		else if (!(error = stream->write(stream, buffer, read_len)))
+			file_size -= read_len;
 	}
 
 	p_close(fd);
-	error = stream->finalize_write(oid, stream);
 
-cleanup:
+	if (!error)
+		error = stream->finalize_write(oid, stream);
+
 	stream->free(stream);
 	return error;
 }
@@ -117,8 +109,7 @@ static int write_file_filtered(
 	git_buf source = GIT_BUF_INIT;
 	git_buf dest = GIT_BUF_INIT;
 
-	error = git_futils_readbuffer(&source, full_path);
-	if (error < GIT_SUCCESS)
+	if ((error = git_futils_readbuffer(&source, full_path)) < 0)
 		return error;
 
 	error = git_filters_apply(&dest, &source, filters);
@@ -127,30 +118,29 @@ static int write_file_filtered(
 	 * and we don't want to ODB write to choke */
 	git_buf_free(&source);
 
-	if (error == GIT_SUCCESS) {
-		/* Write the file to disk if it was properly filtered */
+	/* Write the file to disk if it was properly filtered */
+	if (!error)
 		error = git_odb_write(oid, odb, dest.ptr, dest.size, GIT_OBJ_BLOB);
-	}
 
 	git_buf_free(&dest);
-	return GIT_SUCCESS;
+	return error;
 }
 
-static int write_symlink(git_oid *oid, git_odb *odb, const char *path, size_t link_size)
+static int write_symlink(
+	git_oid *oid, git_odb *odb, const char *path, size_t link_size)
 {
 	char *link_data;
 	ssize_t read_len;
 	int error;
 
 	link_data = git__malloc(link_size);
-	if (!link_data)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(link_data);
 
 	read_len = p_readlink(path, link_data, link_size);
-
 	if (read_len != (ssize_t)link_size) {
+		giterr_set(GITERR_OS, "Failed to create blob.  Can't read symlink '%s'", path);
 		free(link_data);
-		return git__throw(GIT_EOSERR, "Failed to create blob. Can't read symlink");
+		return -1;
 	}
 
 	error = git_odb_write(oid, odb, (void *)link_data, link_size, GIT_OBJ_BLOB);
@@ -168,25 +158,18 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 	git_odb *odb = NULL;
 
 	workdir = git_repository_workdir(repo);
-	if (workdir == NULL)
-		return git__throw(GIT_ENOTFOUND, "Failed to create blob. (No working directory found)");
+	assert(workdir); /* error to call this on bare repo */
 
-	error = git_buf_joinpath(&full_path, workdir, path);
-	if (error < GIT_SUCCESS)
+	if ((error = git_buf_joinpath(&full_path, workdir, path)) < 0 ||
+		(error = git_path_lstat(full_path.ptr, &st)) < 0 ||
+		(error = git_repository_odb__weakptr(&odb, repo)) < 0)
+	{
+		git_buf_free(&full_path);
 		return error;
-
-	error = p_lstat(full_path.ptr, &st);
-	if (error < 0) {
-		error = git__throw(GIT_EOSERR, "Failed to stat blob. %s", strerror(errno));
-		goto cleanup;
 	}
 
 	size = st.st_size;
 
-	error = git_repository_odb__weakptr(&odb, repo);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
 	if (S_ISLNK(st.st_mode)) {
 		error = write_symlink(oid, odb, full_path.ptr, (size_t)size);
 	} else {
@@ -194,12 +177,12 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 		int filter_count;
 
 		/* Load the filters for writing this file to the ODB */
-		filter_count = git_filters_load(&write_filters, repo, path, GIT_FILTER_TO_ODB);
+		filter_count = git_filters_load(
+			&write_filters, repo, path, GIT_FILTER_TO_ODB);
 
 		if (filter_count < 0) {
 			/* Negative value means there was a critical error */
 			error = filter_count;
-			goto cleanup;
 		} else if (filter_count == 0) {
 			/* No filters need to be applied to the document: we can stream
 			 * directly from disk */
@@ -212,19 +195,20 @@ int git_blob_create_fromfile(git_oid *oid, git_repository *repo, const char *pat
 		git_filters_free(&write_filters);
 
 		/*
-		 * TODO: eventually support streaming filtered files, for files which are bigger
-		 * than a given threshold. This is not a priority because applying a filter in
-		 * streaming mode changes the final size of the blob, and without knowing its
-		 * final size, the blob cannot be written in stream mode to the ODB.
+		 * TODO: eventually support streaming filtered files, for files
+		 * which are bigger than a given threshold. This is not a priority
+		 * because applying a filter in streaming mode changes the final
+		 * size of the blob, and without knowing its final size, the blob
+		 * cannot be written in stream mode to the ODB.
 		 *
-		 * The plan is to do streaming writes to a tempfile on disk and then opening
-		 * streaming that file to the ODB, using `write_file_stream`.
+		 * The plan is to do streaming writes to a tempfile on disk and then
+		 * opening streaming that file to the ODB, using
+		 * `write_file_stream`.
 		 *
 		 * CAREFULLY DESIGNED APIS YO
 		 */
 	}
 
-cleanup:
 	git_buf_free(&full_path);
 	return error;
 }
diff --git a/src/buffer.c b/src/buffer.c
index dd245e2..b0e3299 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -215,8 +215,8 @@ void git_buf_truncate(git_buf *buf, size_t len)
 
 void git_buf_rtruncate_at_char(git_buf *buf, char separator)
 {
-	int idx = git_buf_rfind_next(buf, separator);
-	git_buf_truncate(buf, idx < 0 ? 0 : idx);
+	ssize_t idx = git_buf_rfind_next(buf, separator);
+	git_buf_truncate(buf, idx < 0 ? 0 : (size_t)idx);
 }
 
 void git_buf_swap(git_buf *buf_a, git_buf *buf_b)
diff --git a/src/buffer.h b/src/buffer.h
index 6f59dce..d90db4d 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -102,9 +102,9 @@ void git_buf_copy_cstr(char *data, size_t datasize, const git_buf *buf);
 
 #define git_buf_PUTS(buf, str) git_buf_put(buf, str, sizeof(str) - 1)
 
-GIT_INLINE(int) git_buf_rfind_next(git_buf *buf, char ch)
+GIT_INLINE(ssize_t) git_buf_rfind_next(git_buf *buf, char ch)
 {
-	int idx = buf->size - 1;
+	ssize_t idx = (ssize_t)buf->size - 1;
 	while (idx >= 0 && buf->ptr[idx] == ch) idx--;
 	while (idx >= 0 && buf->ptr[idx] != ch) idx--;
 	return idx;
diff --git a/src/errors.c b/src/errors.c
index 6fb7777..70aa641 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -40,7 +40,7 @@ static struct {
 	{GIT_EEXISTS, "A reference with this name already exists"},
 	{GIT_EOVERFLOW, "The given integer literal is too large to be parsed"},
 	{GIT_ENOTNUM, "The given literal is not a valid number"},
-	{GIT_EAMBIGUOUSOIDPREFIX, "The given oid prefix is ambiguous"},
+	{GIT_EAMBIGUOUS, "The given oid prefix is ambiguous"},
 };
 
 const char *git_strerror(int num)
@@ -123,15 +123,43 @@ void giterr_set(int error_class, const char *string, ...)
 	char error_str[1024];
 	va_list arglist;
 
+	/* Grab errno before calling vsnprintf() so it won't be overwritten */
+	const char *os_error_msg =
+		(error_class == GITERR_OS && errno != 0) ? strerror(errno) : NULL;
+#ifdef GIT_WIN32
+	DWORD dwLastError = GetLastError();
+#endif
+
 	va_start(arglist, string);
 	p_vsnprintf(error_str, sizeof(error_str), string, arglist);
 	va_end(arglist);
 
 	/* automatically suffix strerror(errno) for GITERR_OS errors */
 	if (error_class == GITERR_OS) {
-		strncat(error_str, ": ", sizeof(error_str));
-		strncat(error_str, strerror(errno), sizeof(error_str));
-		errno = 0;
+		if (os_error_msg != NULL) {
+			strncat(error_str, ": ", sizeof(error_str));
+			strncat(error_str, os_error_msg, sizeof(error_str));
+			errno = 0; /* reset so same error won't be reported twice */
+		}
+#ifdef GIT_WIN32
+		else if (dwLastError != 0) {
+			LPVOID lpMsgBuf = NULL;
+
+			FormatMessage(
+				FORMAT_MESSAGE_ALLOCATE_BUFFER | 
+				FORMAT_MESSAGE_FROM_SYSTEM |
+				FORMAT_MESSAGE_IGNORE_INSERTS,
+				NULL, dwLastError, 0, (LPTSTR) &lpMsgBuf, 0, NULL);
+
+			if (lpMsgBuf) {
+				strncat(error_str, ": ", sizeof(error_str));
+				strncat(error_str, (const char *)lpMsgBuf, sizeof(error_str));
+				LocalFree(lpMsgBuf);
+			}
+
+			SetLastError(0);
+		}
+#endif
 	}
 
 	giterr_set_str(error_class, error_str);
@@ -165,3 +193,14 @@ void giterr_clear(void)
 {
 	GIT_GLOBAL->last_error = NULL;
 }
+
+const git_error *git_error_last(void)
+{
+	return GIT_GLOBAL->last_error;
+}
+
+void git_error_clear(void)
+{
+	giterr_clear();
+}
+
diff --git a/src/filebuf.c b/src/filebuf.c
index 5e206c5..09b1e0e 100644
--- a/src/filebuf.c
+++ b/src/filebuf.c
@@ -67,6 +67,8 @@ static int lock_file(git_filebuf *file, int flags)
 	if (file->fd < 0)
 		return -1;
 
+	file->fd_is_open = true;
+
 	if ((flags & GIT_FILEBUF_APPEND) && git_path_exists(file->path_original) == true) {
 		git_file source;
 		char buffer[2048];
@@ -94,10 +96,10 @@ static int lock_file(git_filebuf *file, int flags)
 
 void git_filebuf_cleanup(git_filebuf *file)
 {
-	if (file->fd >= 0)
+	if (file->fd_is_open && file->fd >= 0)
 		p_close(file->fd);
 
-	if (file->fd >= 0 && file->path_lock && git_path_exists(file->path_lock) == true)
+	if (file->fd_is_open && file->path_lock && git_path_exists(file->path_lock))
 		p_unlink(file->path_lock);
 
 	if (file->digest)
@@ -239,6 +241,7 @@ int git_filebuf_open(git_filebuf *file, const char *path, int flags)
 			git_buf_free(&tmp_path);
 			goto cleanup;
 		}
+		file->fd_is_open = true;
 
 		/* No original path */
 		file->path_original = NULL;
@@ -308,6 +311,7 @@ int git_filebuf_commit(git_filebuf *file, mode_t mode)
 
 	p_close(file->fd);
 	file->fd = -1;
+	file->fd_is_open = false;
 
 	if (p_chmod(file->path_lock, mode)) {
 		giterr_set(GITERR_OS, "Failed to set attributes for file at '%s'", file->path_lock);
diff --git a/src/filebuf.h b/src/filebuf.h
index 5f9d4ad..19e1797 100644
--- a/src/filebuf.h
+++ b/src/filebuf.h
@@ -40,6 +40,7 @@ struct git_filebuf {
 
 	size_t buf_size, buf_pos;
 	git_file fd;
+	bool fd_is_open;
 	int last_error;
 };
 
diff --git a/src/fileops.c b/src/fileops.c
index c9fd2c5..aa52b09 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -79,11 +79,25 @@ int git_futils_creat_locked_withpath(const char *path, const mode_t dirmode, con
 	return git_futils_creat_locked(path, mode);
 }
 
+int git_futils_open_ro(const char *path)
+{
+	int fd = p_open(path, O_RDONLY);
+	if (fd < 0) {
+		if (errno == ENOENT)
+			fd = GIT_ENOTFOUND;
+		giterr_set(GITERR_OS, "Failed to open '%s'", path);
+	}
+	return fd;
+}
+
 git_off_t git_futils_filesize(git_file fd)
 {
 	struct stat sb;
-	if (p_fstat(fd, &sb))
-		return GIT_ERROR;
+
+	if (p_fstat(fd, &sb)) {
+		giterr_set(GITERR_OS, "Failed to stat file descriptor");
+		return -1;
+	}
 
 	return sb.st_size;
 }
@@ -117,7 +131,7 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 		return fd;
 
 	if (p_fstat(fd, &st) < 0 || S_ISDIR(st.st_mode) || !git__is_sizet(st.st_size+1)) {
-		close(fd);
+		p_close(fd);
 		giterr_set(GITERR_OS, "Invalid regular file stat for '%s'", path);
 		return -1;
 	}
@@ -127,7 +141,7 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 	 * has been modified.
 	 */
 	if (mtime != NULL && *mtime >= st.st_mtime) {
-		close(fd);
+		p_close(fd);
 		return 0;
 	}
 
@@ -139,8 +153,8 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 	git_buf_clear(buf);
 
 	if (git_buf_grow(buf, len + 1) < 0) {
-		close(fd);
-		return GIT_ENOMEM;
+		p_close(fd);
+		return -1;
 	}
 
 	buf->ptr[len] = '\0';
@@ -149,7 +163,7 @@ int git_futils_readbuffer_updated(git_buf *buf, const char *path, time_t *mtime,
 		ssize_t read_size = p_read(fd, buf->ptr, len);
 
 		if (read_size < 0) {
-			close(fd);
+			p_close(fd);
 			giterr_set(GITERR_OS, "Failed to read descriptor for '%s'", path);
 			return -1;
 		}
@@ -176,10 +190,15 @@ int git_futils_readbuffer(git_buf *buf, const char *path)
 
 int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmode)
 {
-	if (git_futils_mkpath2file(to, dirmode) < GIT_SUCCESS)
-		return GIT_EOSERR;	/* The callee already takes care of setting the correct error message. */
+	if (git_futils_mkpath2file(to, dirmode) < 0)
+		return -1;
+
+	if (p_rename(from, to) < 0) {
+		giterr_set(GITERR_OS, "Failed to rename '%s' to '%s'", from, to);
+		return -1;
+	}
 
-	return p_rename(from, to); /* The callee already takes care of setting the correct error message. */
+	return 0;
 }
 
 int git_futils_mmap_ro(git_map *out, git_file fd, git_off_t begin, size_t len)
@@ -192,8 +211,10 @@ int git_futils_mmap_ro_file(git_map *out, const char *path)
 	git_file fd = p_open(path, O_RDONLY /* | O_NOATIME */);
 	git_off_t len = git_futils_filesize(fd);
 	int result;
-	if (!git__is_sizet(len))
-		return git__throw(GIT_ERROR, "File `%s` too large to mmap", path);
+	if (!git__is_sizet(len)) {
+		giterr_set(GITERR_OS, "File `%s` too large to mmap", path);
+		return -1;
+	}
 	result = git_futils_mmap_ro(out, fd, 0, (size_t)len);
 	p_close(fd);
 	return result;
@@ -260,20 +281,31 @@ int git_futils_mkdir_r(const char *path, const char *base, const mode_t mode)
 
 static int _rmdir_recurs_foreach(void *opaque, git_buf *path)
 {
-	int error = GIT_SUCCESS;
 	int force = *(int *)opaque;
 
 	if (git_path_isdir(path->ptr) == true) {
-		error = git_path_direach(path, _rmdir_recurs_foreach, opaque);
-		if (error < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to remove directory `%s`", path->ptr);
-		return p_rmdir(path->ptr);
+		if (git_path_direach(path, _rmdir_recurs_foreach, opaque) < 0)
+			return -1;
+
+		if (p_rmdir(path->ptr) < 0) {
+			giterr_set(GITERR_OS, "Could not remove directory '%s'", path->ptr);
+			return -1;
+		}
 
-	} else if (force) {
-		return p_unlink(path->ptr);
+		return 0;
 	}
 
-	return git__rethrow(error, "Failed to remove directory. `%s` is not empty", path->ptr);
+	if (force) {
+		if (p_unlink(path->ptr) < 0) {
+			giterr_set(GITERR_OS, "Could not remove directory.  File '%s' cannot be removed", path->ptr);
+			return -1;
+		}
+
+		return 0;
+	}
+
+	giterr_set(GITERR_OS, "Could not remove directory. File '%s' still present", path->ptr);
+	return -1;
 }
 
 int git_futils_rmdir_r(const char *path, int force)
@@ -282,7 +314,7 @@ int git_futils_rmdir_r(const char *path, int force)
 	git_buf p = GIT_BUF_INIT;
 
 	error = git_buf_sets(&p, path);
-	if (error == GIT_SUCCESS)
+	if (!error)
 		error = _rmdir_recurs_foreach(&force, &p);
 	git_buf_free(&p);
 	return error;
@@ -328,9 +360,8 @@ static const win32_path *win32_system_root(void)
 		const wchar_t *root_tmpl = L"%PROGRAMFILES%\\Git\\etc\\";
 
 		s_root.len = ExpandEnvironmentStringsW(root_tmpl, NULL, 0);
-
 		if (s_root.len <= 0) {
-			git__throw(GIT_EOSERR, "Failed to expand environment strings");
+			giterr_set(GITERR_OS, "Failed to expand environment strings");
 			return NULL;
 		}
 
@@ -339,7 +370,7 @@ static const win32_path *win32_system_root(void)
 			return NULL;
 
 		if (ExpandEnvironmentStringsW(root_tmpl, s_root.path, s_root.len) != s_root.len) {
-			git__throw(GIT_EOSERR, "Failed to expand environment strings");
+			giterr_set(GITERR_OS, "Failed to expand environment strings");
 			git__free(s_root.path);
 			s_root.path = NULL;
 			return NULL;
@@ -351,7 +382,7 @@ static const win32_path *win32_system_root(void)
 
 static int win32_find_system_file(git_buf *path, const char *filename)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 	const win32_path *root = win32_system_root();
 	size_t len;
 	wchar_t *file_utf16 = NULL, *scan;
@@ -362,8 +393,7 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	/* allocate space for wchar_t path to file */
 	file_utf16 = git__calloc(root->len + len + 2, sizeof(wchar_t));
-	if (!file_utf16)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(file_utf16);
 
 	/* append root + '\\' + filename as wchar_t */
 	memcpy(file_utf16, root->path, root->len * sizeof(wchar_t));
@@ -373,7 +403,7 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	if (gitwin_append_utf16(file_utf16 + root->len - 1, filename, len + 1) !=
 		(int)len + 1) {
-		error = git__throw(GIT_EOSERR, "Failed to build file path");
+		error = -1;
 		goto cleanup;
 	}
 
@@ -389,9 +419,8 @@ static int win32_find_system_file(git_buf *path, const char *filename)
 
 	/* convert to utf8 */
 	if ((file_utf8 = gitwin_from_utf16(file_utf16)) == NULL)
-		error = GIT_ENOMEM;
-
-	if (file_utf8) {
+		error = -1;
+	else {
 		git_path_mkposix(file_utf8);
 		git_buf_attach(path, file_utf8, 0);
 	}
@@ -409,7 +438,7 @@ int git_futils_find_system_file(git_buf *path, const char *filename)
 		return -1;
 
 	if (git_path_exists(path->ptr) == true)
-		return GIT_SUCCESS;
+		return 0;
 
 	git_buf_clear(path);
 
diff --git a/src/fileops.h b/src/fileops.h
index c2ba8ff..6df5653 100644
--- a/src/fileops.h
+++ b/src/fileops.h
@@ -77,18 +77,9 @@ extern int git_futils_mktmp(git_buf *path_out, const char *filename);
 extern int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmode);
 
 /**
- * Open a file readonly and set error if needed
- */
-GIT_INLINE(int) git_futils_open_ro(const char *path)
-{
-	int fd = p_open(path, O_RDONLY);
-	if (fd < 0) {
-		if (errno == ENOENT)
-			fd = GIT_ENOTFOUND;
-		giterr_set(GITERR_OS, "Failed to open '%s'", path);
-	}
-	return fd;
-}
+ * Open a file readonly and set error if needed.
+ */
+extern int git_futils_open_ro(const char *path);
 
 /**
  * Get the filesize in bytes of a file
diff --git a/src/hashtable.c b/src/hashtable.c
index c081fc9..8e057d4 100644
--- a/src/hashtable.c
+++ b/src/hashtable.c
@@ -31,9 +31,7 @@ static int resize_to(git_hashtable *self, size_t new_size)
 		self->size_mask = new_size - 1;
 		self->key_count = 0;
 		self->nodes = git__calloc(1, sizeof(git_hashtable_node) * self->size);
-
-		if (self->nodes == NULL)
-			return GIT_ENOMEM;
+		GITERR_CHECK_ALLOC(self->nodes);
 
 		if (insert_nodes(self, old_nodes, old_size) == 0)
 			self->is_resizing = 0;
@@ -44,22 +42,22 @@ static int resize_to(git_hashtable *self, size_t new_size)
 	} while(self->is_resizing);
 
 	git__free(old_nodes);
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int set_size(git_hashtable *self, size_t new_size)
 {
 	self->nodes = git__realloc(self->nodes, new_size * sizeof(git_hashtable_node));
-	if (self->nodes == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(self->nodes);
 
 	if (new_size > self->size) {
-		memset(&self->nodes[self->size], 0x0, (new_size - self->size) * sizeof(git_hashtable_node));
+		memset(&self->nodes[self->size], 0x0,
+			(new_size - self->size) * sizeof(git_hashtable_node));
 	}
 
 	self->size = new_size;
 	self->size_mask = new_size - 1;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static git_hashtable_node *node_with_hash(git_hashtable *self, const void *key, int hash_id)
@@ -84,43 +82,47 @@ static int node_insert(git_hashtable *self, git_hashtable_node *new_node)
 			git_hashtable_node *node;
 			node = node_with_hash(self, new_node->key, hash_id);
 			node_swap_with(new_node, node);
-			if(new_node->key == 0x0){
+			if (new_node->key == 0x0){
 				self->key_count++;
-				return GIT_SUCCESS;
+				return 0;
 			}
 		}
 	}
 
-	if (self->is_resizing)
-		return git__throw(GIT_EBUSY, "Failed to insert node. Hashtable is currently resizing");
+	/* Failed to insert node. Hashtable is currently resizing */
+	assert(!self->is_resizing);
+
+	if (resize_to(self, self->size * 2) < 0)
+		return -1;
 
-	resize_to(self, self->size * 2);
-	git_hashtable_insert(self, new_node->key, new_node->value);
-	return GIT_SUCCESS;
+	return git_hashtable_insert(self, new_node->key, new_node->value);
 }
 
-static int insert_nodes(git_hashtable *self, git_hashtable_node *old_nodes, size_t old_size)
+static int insert_nodes(
+	git_hashtable *self, git_hashtable_node *old_nodes, size_t old_size)
 {
 	size_t i;
 
 	for (i = 0; i < old_size; ++i) {
 		git_hashtable_node *node = git_hashtable_node_at(old_nodes, i);
-		if (node->key && git_hashtable_insert(self, node->key, node->value) < GIT_SUCCESS)
-			return GIT_ENOMEM;
+		if (node->key &&
+			git_hashtable_insert(self, node->key, node->value) < 0)
+			return -1;
 	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
-git_hashtable *git_hashtable_alloc(size_t min_size,
-		git_hash_ptr hash,
-		git_hash_keyeq_ptr key_eq)
+git_hashtable *git_hashtable_alloc(
+	size_t min_size,
+	git_hash_ptr hash,
+	git_hash_keyeq_ptr key_eq)
 {
 	git_hashtable *table;
 
 	assert(hash && key_eq);
 
-	if ((table = git__malloc(sizeof(git_hashtable))) == NULL)
+	if ((table = git__malloc(sizeof(*table))) == NULL)
 		return NULL;
 
 	memset(table, 0x0, sizeof(git_hashtable));
@@ -161,7 +163,8 @@ void git_hashtable_free(git_hashtable *self)
 }
 
 
-int git_hashtable_insert2(git_hashtable *self, const void *key, void *value, void **old_value)
+int git_hashtable_insert2(
+	git_hashtable *self, const void *key, void *value, void **old_value)
 {
 	int hash_id;
 	git_hashtable_node *node;
@@ -177,14 +180,14 @@ int git_hashtable_insert2(git_hashtable *self, const void *key, void *value, voi
 			node->key = key;
 			node->value = value;
 			self->key_count++;
-			return GIT_SUCCESS;
+			return 0;
 		}
 
 		if (key == node->key || self->key_equal(key, node->key) == 0) {
 			*old_value = node->value;
 			node->key = key;
 			node->value = value;
-			return GIT_SUCCESS;
+			return 0;
 		}
 	}
 
@@ -213,7 +216,8 @@ void *git_hashtable_lookup(git_hashtable *self, const void *key)
 	return NULL;
 }
 
-int git_hashtable_remove2(git_hashtable *self, const void *key, void **old_value)
+int git_hashtable_remove2(
+	git_hashtable *self, const void *key, void **old_value)
 {
 	int hash_id;
 	git_hashtable_node *node;
@@ -236,8 +240,8 @@ int git_hashtable_remove2(git_hashtable *self, const void *key, void **old_value
 
 int git_hashtable_merge(git_hashtable *self, git_hashtable *other)
 {
-	if (resize_to(self, (self->size + other->size) * 2) < GIT_SUCCESS)
-		return GIT_ENOMEM;
+	if (resize_to(self, (self->size + other->size) * 2) < 0)
+		return -1;
 
 	return insert_nodes(self, other->nodes, other->key_count);
 }
@@ -254,5 +258,10 @@ uint32_t git_hash__strhash_cb(const void *key, int hash_id)
 		0x7daaab3c
 	};
 
-	return git__hash(key, strlen((const char *)key), hash_seeds[hash_id]);
+	size_t key_len = strlen((const char *)key);
+
+	/* won't take hash of strings longer than 2^31 right now */
+	assert(key_len == (size_t)((int)key_len));
+
+	return git__hash(key, (int)key_len, hash_seeds[hash_id]);
 }
diff --git a/src/hashtable.h b/src/hashtable.h
index e099659..0bab845 100644
--- a/src/hashtable.h
+++ b/src/hashtable.h
@@ -66,7 +66,7 @@ GIT_INLINE(int) git_hashtable_insert(git_hashtable *h, const void *key, void *va
 #define git_hashtable_node_at(nodes, pos) ((git_hashtable_node *)(&nodes[pos]))
 
 #define GIT_HASHTABLE__FOREACH(self,block) { \
-	unsigned int _c; \
+	size_t _c; \
 	git_hashtable_node *_n = (self)->nodes; \
 	for (_c = (self)->size; _c > 0; _c--, _n++)	{ \
 		if (!_n->key) continue; block } }
diff --git a/src/ignore.c b/src/ignore.c
index a3bf0a2..4cbc55d 100644
--- a/src/ignore.c
+++ b/src/ignore.c
@@ -168,9 +168,9 @@ static int ignore_lookup_in_rules(
 	git_attr_fnmatch *match;
 
 	git_vector_rforeach(rules, j, match) {
-		if (git_attr_fnmatch__match(match, path) == GIT_SUCCESS) {
+		if (git_attr_fnmatch__match(match, path)) {
 			*ignored = ((match->flags & GIT_ATTR_FNMATCH_NEGATIVE) == 0);
-			return GIT_SUCCESS;
+			return 0;
 		}
 	}
 
diff --git a/src/index.c b/src/index.c
index d5410a3..7f5909a 100644
--- a/src/index.c
+++ b/src/index.c
@@ -319,8 +319,7 @@ static int index_entry_init(git_index_entry **entry_out, git_index *index, const
 	if (error < GIT_SUCCESS)
 		return error;
 
-	if (p_lstat(full_path.ptr, &st) < 0) {
-		error = git__throw(GIT_ENOTFOUND, "Failed to initialize entry. '%s' cannot be opened. %s", full_path.ptr, strerror(errno));
+	if ((error = git_path_lstat(full_path.ptr, &st)) < 0) {
 		git_buf_free(&full_path);
 		return error;
 	}
diff --git a/src/indexer.c b/src/indexer.c
index dd7c719..6f8bd32 100644
--- a/src/indexer.c
+++ b/src/indexer.c
@@ -133,12 +133,15 @@ int git_indexer_new(git_indexer **out, const char *packname)
 
 	idx->nr_objects = ntohl(idx->hdr.hdr_entries);
 
-	error = git_vector_init(&idx->pack->cache, idx->nr_objects, cache_cmp);
+	/* for now, limit to 2^32 objects */
+	assert(idx->nr_objects == (size_t)((unsigned int)idx->nr_objects));
+
+	error = git_vector_init(&idx->pack->cache, (unsigned int)idx->nr_objects, cache_cmp);
 	if (error < GIT_SUCCESS)
 		goto cleanup;
 
 	idx->pack->has_cache = 1;
-	error = git_vector_init(&idx->objects, idx->nr_objects, objects_cmp);
+	error = git_vector_init(&idx->objects, (unsigned int)idx->nr_objects, objects_cmp);
 	if (error < GIT_SUCCESS)
 		goto cleanup;
 
@@ -307,7 +310,7 @@ cleanup:
 int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 {
 	git_mwindow_file *mwf;
-	off_t off = sizeof(struct git_pack_header);
+	git_off_t off = sizeof(struct git_pack_header);
 	int error;
 	struct entry *entry;
 	unsigned int left, processed;
@@ -319,7 +322,7 @@ int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 	if (error < GIT_SUCCESS)
 		return git__rethrow(error, "Failed to register mwindow file");
 
-	stats->total = idx->nr_objects;
+	stats->total = (unsigned int)idx->nr_objects;
 	stats->processed = processed = 0;
 
 	while (processed < idx->nr_objects) {
@@ -328,18 +331,18 @@ int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 		struct git_pack_entry *pentry;
 		git_mwindow *w = NULL;
 		int i;
-		off_t entry_start = off;
+		git_off_t entry_start = off;
 		void *packed;
 		size_t entry_size;
 
-		entry = git__malloc(sizeof(struct entry));
-		memset(entry, 0x0, sizeof(struct entry));
+		entry = git__calloc(1, sizeof(*entry));
+		GITERR_CHECK_ALLOC(entry);
 
 		if (off > UINT31_MAX) {
 			entry->offset = UINT32_MAX;
 			entry->offset_long = off;
 		} else {
-			entry->offset = off;
+			entry->offset = (uint32_t)off;
 		}
 
 		error = git_packfile_unpack(&obj, idx->pack, &off);
@@ -369,13 +372,13 @@ int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
 		git_oid_cpy(&entry->oid, &oid);
 		entry->crc = crc32(0L, Z_NULL, 0);
 
-		entry_size = off - entry_start;
+		entry_size = (size_t)(off - entry_start);
 		packed = git_mwindow_open(mwf, &w, entry_start, entry_size, &left);
 		if (packed == NULL) {
 			error = git__rethrow(error, "Failed to open window to read packed data");
 			goto cleanup;
 		}
-		entry->crc = htonl(crc32(entry->crc, packed, entry_size));
+		entry->crc = htonl(crc32(entry->crc, packed, (uInt)entry_size));
 		git_mwindow_close(&w);
 
 		/* Add the object to the list */
diff --git a/src/iterator.c b/src/iterator.c
index 0ce89df..c10b9ff 100644
--- a/src/iterator.c
+++ b/src/iterator.c
@@ -309,7 +309,7 @@ static int workdir_iterator__expand_dir(workdir_iterator *wi)
 
 	/* only push new ignores if this is not top level directory */
 	if (wi->stack->next != NULL) {
-		int slash_pos = git_buf_rfind_next(&wi->path, '/');
+		ssize_t slash_pos = git_buf_rfind_next(&wi->path, '/');
 		(void)git_ignore__push_dir(&wi->ignores, &wi->path.ptr[slash_pos + 1]);
 	}
 
diff --git a/src/map.h b/src/map.h
index 0b070fa..96d8795 100644
--- a/src/map.h
+++ b/src/map.h
@@ -31,6 +31,11 @@ typedef struct { /* memory mapped buffer	*/
 #endif
 } git_map;
 
+#define GIT_MMAP_VALIDATE(out, len, prot, flags) do { \
+	assert(out != NULL && len > 0); \
+	assert((prot & GIT_PROT_WRITE) || (prot & GIT_PROT_READ)); \
+	assert((flags & GIT_MAP_FIXED) == 0); } while (0)
+
 extern int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offset);
 extern int p_munmap(git_map *map);
 
diff --git a/src/mwindow.c b/src/mwindow.c
index 39f6aea..cde24d1 100644
--- a/src/mwindow.c
+++ b/src/mwindow.c
@@ -178,8 +178,10 @@ static git_mwindow *new_window(
 	 * window.
 	 */
 
-	if (git_futils_mmap_ro(&w->window_map, fd, w->offset, (size_t)len) < GIT_SUCCESS)
-		goto cleanup;
+	if (git_futils_mmap_ro(&w->window_map, fd, w->offset, (size_t)len) < 0) {
+		git__free(w);
+		return NULL;
+	}
 
 	ctl->mmap_calls++;
 	ctl->open_windows++;
@@ -191,10 +193,6 @@ static git_mwindow *new_window(
 		ctl->peak_open_windows = ctl->open_windows;
 
 	return w;
-
-cleanup:
-	git__free(w);
-	return NULL;
 }
 
 /*
@@ -205,7 +203,7 @@ unsigned char *git_mwindow_open(
 	git_mwindow_file *mwf,
 	git_mwindow **cursor,
 	git_off_t offset,
-	int extra,
+	size_t extra,
 	unsigned int *left)
 {
 	git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
@@ -253,11 +251,10 @@ unsigned char *git_mwindow_open(
 int git_mwindow_file_register(git_mwindow_file *mwf)
 {
 	git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
-	int error;
 
 	if (ctl->windowfiles.length == 0 &&
-		(error = git_vector_init(&ctl->windowfiles, 8, NULL)) < GIT_SUCCESS)
-		return error;
+		git_vector_init(&ctl->windowfiles, 8, NULL) < 0)
+		return -1;
 
 	return git_vector_insert(&ctl->windowfiles, mwf);
 }
diff --git a/src/mwindow.h b/src/mwindow.h
index 94bfb5d..0580272 100644
--- a/src/mwindow.h
+++ b/src/mwindow.h
@@ -15,8 +15,8 @@ typedef struct git_mwindow {
 	struct git_mwindow *next;
 	git_map window_map;
 	git_off_t offset;
-	unsigned int last_used;
-	unsigned int inuse_cnt;
+	size_t last_used;
+	size_t inuse_cnt;
 } git_mwindow;
 
 typedef struct git_mwindow_file {
@@ -37,7 +37,7 @@ typedef struct git_mwindow_ctl {
 
 int git_mwindow_contains(git_mwindow *win, git_off_t offset);
 void git_mwindow_free_all(git_mwindow_file *mwf);
-unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, int extra, unsigned int *left);
+unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, size_t extra, unsigned int *left);
 void git_mwindow_scan_lru(git_mwindow_file *mwf, git_mwindow **lru_w, git_mwindow **lru_l);
 int git_mwindow_file_register(git_mwindow_file *mwf);
 void git_mwindow_close(git_mwindow **w_cursor);
diff --git a/src/object.c b/src/object.c
index 0430015..bb27f71 100644
--- a/src/object.c
+++ b/src/object.c
@@ -92,7 +92,7 @@ int git_object_lookup_prefix(
 	assert(repo && object_out && id);
 
 	if (len < GIT_OID_MINPREFIXLEN)
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX,
+		return git__throw(GIT_EAMBIGUOUS,
 			"Failed to lookup object. Prefix length is lower than %d.", GIT_OID_MINPREFIXLEN);
 
 	error = git_repository_odb__weakptr(&odb, repo);
diff --git a/src/odb.c b/src/odb.c
index edb9c72..f68d135 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -145,10 +145,8 @@ int git_odb__hashlink(git_oid *out, const char *path)
 	git_off_t size;
 	int result;
 
-	if (p_lstat(path, &st) < 0) {
-		giterr_set(GITERR_OS, "Failed to stat object '%s'", path);
+	if (git_path_lstat(path, &st) < 0)
 		return -1;
-	}
 
 	size = st.st_size;
 
@@ -188,7 +186,7 @@ int git_odb_hashfile(git_oid *out, const char *path, git_otype type)
 	git_off_t size;
 	int result, fd = git_futils_open_ro(path);
 	if (fd < 0)
-		return -1;
+		return fd;
 
 	if ((size = git_futils_filesize(fd)) < 0 || !git__is_sizet(size)) {
 		giterr_set(GITERR_OS, "File size overflow for 32-bit systems");
@@ -507,23 +505,20 @@ int git_odb_read_header(size_t *len_p, git_otype *type_p, git_odb *db, const git
 			error = b->read_header(len_p, type_p, b, id);
 	}
 
-	if (error == GIT_EPASSTHROUGH)
+	if (!error || error == GIT_EPASSTHROUGH)
 		return 0;
 
 	/*
 	 * no backend could read only the header.
 	 * try reading the whole object and freeing the contents
 	 */
-	if (error < 0) {
-		if ((error = git_odb_read(&object, db, id)) < GIT_SUCCESS)
-			return error; /* error already set - pass through */
-
-		*len_p = object->raw.len;
-		*type_p = object->raw.type;
-		git_odb_object_free(object);
-	}
+	if ((error = git_odb_read(&object, db, id)) < 0)
+		return error; /* error already set - pass along */
 
-	return GIT_SUCCESS;
+	*len_p = object->raw.len;
+	*type_p = object->raw.type;
+	git_odb_object_free(object);
+	return 0;
 }
 
 int git_odb_read(git_odb_object **out, git_odb *db, const git_oid *id)
@@ -536,7 +531,7 @@ int git_odb_read(git_odb_object **out, git_odb *db, const git_oid *id)
 
 	*out = git_cache_get(&db->cache, id);
 	if (*out != NULL)
-		return GIT_SUCCESS;
+		return 0;
 
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
@@ -546,15 +541,15 @@ int git_odb_read(git_odb_object **out, git_odb *db, const git_oid *id)
 			error = b->read(&raw.data, &raw.len, &raw.type, b, id);
 	}
 
-	if (error == GIT_EPASSTHROUGH || error == GIT_SUCCESS) {
-		*out = git_cache_try_store(&db->cache, new_odb_object(id, &raw));
-		return GIT_SUCCESS;
-	}
+	if (error && error != GIT_EPASSTHROUGH)
+		return error;
 
-	return git__rethrow(error, "Failed to read object");
+	*out = git_cache_try_store(&db->cache, new_odb_object(id, &raw));
+	return 0;
 }
 
-int git_odb_read_prefix(git_odb_object **out, git_odb *db, const git_oid *short_id, unsigned int len)
+int git_odb_read_prefix(
+	git_odb_object **out, git_odb *db, const git_oid *short_id, unsigned int len)
 {
 	unsigned int i;
 	int error = GIT_ENOTFOUND;
@@ -565,7 +560,7 @@ int git_odb_read_prefix(git_odb_object **out, git_odb *db, const git_oid *short_
 	assert(out && db);
 
 	if (len < GIT_OID_MINPREFIXLEN)
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to lookup object. Prefix length is lower than %d.", GIT_OID_MINPREFIXLEN);
+		return git_odb__error_ambiguous("prefix length too short");
 
 	if (len > GIT_OID_HEXSZ)
 		len = GIT_OID_HEXSZ;
@@ -573,7 +568,7 @@ int git_odb_read_prefix(git_odb_object **out, git_odb *db, const git_oid *short_
 	if (len == GIT_OID_HEXSZ) {
 		*out = git_cache_get(&db->cache, short_id);
 		if (*out != NULL)
-			return GIT_SUCCESS;
+			return 0;
 	}
 
 	for (i = 0; i < db->backends.length && found < 2; ++i) {
@@ -582,33 +577,24 @@ int git_odb_read_prefix(git_odb_object **out, git_odb *db, const git_oid *short_
 
 		if (b->read != NULL) {
 			error = b->read_prefix(&full_oid, &raw.data, &raw.len, &raw.type, b, short_id, len);
-			switch (error) {
-			case GIT_SUCCESS:
+			if (!error)
 				found++;
-				break;
-			case GIT_ENOTFOUND:
-			case GIT_EPASSTHROUGH:
-				break;
-			case GIT_EAMBIGUOUSOIDPREFIX:
-				return git__rethrow(error, "Failed to read object. Ambiguous sha1 prefix");
-			default:
-				return git__rethrow(error, "Failed to read object");
-			}
+			else if (error != GIT_ENOTFOUND && error != GIT_EPASSTHROUGH)
+				return error;
 		}
 	}
 
-	if (found == 1) {
-		*out = git_cache_try_store(&db->cache, new_odb_object(&full_oid, &raw));
-	} else if (found > 1) {
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to read object. Ambiguous sha1 prefix");
-	} else {
-		return git__throw(GIT_ENOTFOUND, "Failed to read object. Object not found");
-	}
+	if (found == 0)
+		return git_odb__error_notfound("no match for prefix");
+	if (found > 1)
+		return git_odb__error_ambiguous("multiple matches for prefix");
 
-	return GIT_SUCCESS;
+	*out = git_cache_try_store(&db->cache, new_odb_object(&full_oid, &raw));
+	return 0;
 }
 
-int git_odb_write(git_oid *oid, git_odb *db, const void *data, size_t len, git_otype type)
+int git_odb_write(
+	git_oid *oid, git_odb *db, const void *data, size_t len, git_otype type)
 {
 	unsigned int i;
 	int error = GIT_ERROR;
@@ -628,24 +614,25 @@ int git_odb_write(git_oid *oid, git_odb *db, const void *data, size_t len, git_o
 			error = b->write(oid, b, data, len, type);
 	}
 
-	if (error == GIT_EPASSTHROUGH || error == GIT_SUCCESS)
-		return GIT_SUCCESS;
+	if (!error || error == GIT_EPASSTHROUGH)
+		return 0;
 
 	/* if no backends were able to write the object directly, we try a streaming
 	 * write to the backends; just write the whole object into the stream in one
 	 * push */
 
-	if ((error = git_odb_open_wstream(&stream, db, len, type)) == GIT_SUCCESS) {
-		stream->write(stream, data, len);
-		error = stream->finalize_write(oid, stream);
-		stream->free(stream);
-		return GIT_SUCCESS;
-	}
+	if ((error = git_odb_open_wstream(&stream, db, len, type)) != 0)
+		return error;
 
-	return git__rethrow(error, "Failed to write object");
+	stream->write(stream, data, len);
+	error = stream->finalize_write(oid, stream);
+	stream->free(stream);
+
+	return error;
 }
 
-int git_odb_open_wstream(git_odb_stream **stream, git_odb *db, size_t size, git_otype type)
+int git_odb_open_wstream(
+	git_odb_stream **stream, git_odb *db, size_t size, git_otype type)
 {
 	unsigned int i;
 	int error = GIT_ERROR;
@@ -666,10 +653,10 @@ int git_odb_open_wstream(git_odb_stream **stream, git_odb *db, size_t size, git_
 			error = init_fake_wstream(stream, b, size, type);
 	}
 
-	if (error == GIT_EPASSTHROUGH || error == GIT_SUCCESS)
-		return GIT_SUCCESS;
+	if (error == GIT_EPASSTHROUGH)
+		error = 0;
 
-	return git__rethrow(error, "Failed to open write stream");
+	return error;
 }
 
 int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oid)
@@ -687,9 +674,21 @@ int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oi
 			error = b->readstream(stream, b, oid);
 	}
 
-	if (error == GIT_EPASSTHROUGH || error == GIT_SUCCESS)
-		return GIT_SUCCESS;
+	if (error == GIT_EPASSTHROUGH)
+		error = 0;
 
-	return git__rethrow(error, "Failed to open read stream");
+	return error;
+}
+
+int git_odb__error_notfound(const char *message)
+{
+	giterr_set(GITERR_ODB, "Object not found - %s", message);
+	return GIT_ENOTFOUND;
+}
+
+int git_odb__error_ambiguous(const char *message)
+{
+	giterr_set(GITERR_ODB, "Ambiguous SHA1 prefix - %s", message);
+	return GIT_EAMBIGUOUS;
 }
 
diff --git a/src/odb.h b/src/odb.h
index 2f84ebe..4c425c0 100644
--- a/src/odb.h
+++ b/src/odb.h
@@ -67,4 +67,14 @@ int git_odb__hashfd(git_oid *out, git_file fd, size_t size, git_otype type);
  */
 int git_odb__hashlink(git_oid *out, const char *path);
 
+/*
+ * Generate a GIT_ENOTFOUND error for the ODB.
+ */
+int git_odb__error_notfound(const char *message);
+
+/*
+ * Generate a GIT_EAMBIGUOUS error for the ODB.
+ */
+int git_odb__error_ambiguous(const char *message);
+
 #endif
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 17fede4..c493cc6 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -61,8 +61,8 @@ static int object_file_name(git_buf *name, const char *dir, const git_oid *id)
 	git_buf_sets(name, dir);
 
 	/* expand length for 40 hex sha1 chars + 2 * '/' + '\0' */
-	if (git_buf_grow(name, name->size + GIT_OID_HEXSZ + 3) < GIT_SUCCESS)
-		return GIT_ENOMEM;
+	if (git_buf_grow(name, name->size + GIT_OID_HEXSZ + 3) < 0)
+		return -1;
 
 	git_path_to_dir(name);
 
@@ -71,7 +71,7 @@ static int object_file_name(git_buf *name, const char *dir, const git_oid *id)
 	name->size += GIT_OID_HEXSZ + 1;
 	name->ptr[name->size] = '\0';
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
@@ -199,10 +199,12 @@ static int finish_inflate(z_stream *s)
 
 	inflateEnd(s);
 
-	if ((status != Z_STREAM_END) || (s->avail_in != 0))
-		return git__throw(GIT_ERROR, "Failed to finish inflation. Stream aborted prematurely");
+	if ((status != Z_STREAM_END) || (s->avail_in != 0)) {
+		giterr_set(GITERR_ZLIB, "Failed to finish ZLib inflation. Stream aborted prematurely");
+		return -1;
+	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int is_zlib_compressed_data(unsigned char *data)
@@ -226,21 +228,24 @@ static int inflate_buffer(void *in, size_t inlen, void *out, size_t outlen)
 	zs.next_in = in;
 	zs.avail_in = (uInt)inlen;
 
-	if (inflateInit(&zs) < Z_OK)
-		return git__throw(GIT_ERROR, "Failed to inflate buffer");
+	if (inflateInit(&zs) < Z_OK) {
+		giterr_set(GITERR_ZLIB, "Failed to inflate buffer");
+		return -1;
+	}
 
 	while (status == Z_OK)
 		status = inflate(&zs, Z_FINISH);
 
 	inflateEnd(&zs);
 
-	if ((status != Z_STREAM_END) /*|| (zs.avail_in != 0) */)
-		return git__throw(GIT_ERROR, "Failed to inflate buffer. Stream aborted prematurely");
-
-	if (zs.total_out != outlen)
-		return git__throw(GIT_ERROR, "Failed to inflate buffer. Stream aborted prematurely");
+	if (status != Z_STREAM_END /* || zs.avail_in != 0 */ ||
+		zs.total_out != outlen)
+	{
+		giterr_set(GITERR_ZLIB, "Failed to inflate buffer. Stream aborted prematurely");
+		return -1;
+	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static void *inflate_tail(z_stream *s, void *hb, size_t used, obj_hdr *hdr)
@@ -297,24 +302,23 @@ static int inflate_packlike_loose_disk_obj(git_rawobj *out, git_buf *obj)
 	 * read the object header, which is an (uncompressed)
 	 * binary encoding of the object type and size.
 	 */
-	if ((used = get_binary_object_header(&hdr, obj)) == 0)
-		return git__throw(GIT_ERROR, "Failed to inflate loose object. Object has no header");
-
-	if (!git_object_typeisloose(hdr.type))
-		return git__throw(GIT_ERROR, "Failed to inflate loose object. Wrong object type");
+	if ((used = get_binary_object_header(&hdr, obj)) == 0 ||
+		!git_object_typeisloose(hdr.type)) {
+		giterr_set(GITERR_ODB, "Failed to inflate loose object.");
+		return -1;
+	}
 
 	/*
 	 * allocate a buffer and inflate the data into it
 	 */
 	buf = git__malloc(hdr.size + 1);
-	if (!buf)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(buf);
 
 	in = ((unsigned char *)obj->ptr) + used;
 	len = obj->size - used;
-	if (inflate_buffer(in, len, buf, hdr.size)) {
+	if (inflate_buffer(in, len, buf, hdr.size) < 0) {
 		git__free(buf);
-		return git__throw(GIT_ERROR, "Failed to inflate loose object. Could not inflate buffer");
+		return -1;
 	}
 	buf[hdr.size] = '\0';
 
@@ -322,7 +326,7 @@ static int inflate_packlike_loose_disk_obj(git_rawobj *out, git_buf *obj)
 	out->len = hdr.size;
 	out->type = hdr.type;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int inflate_disk_obj(git_rawobj *out, git_buf *obj)
@@ -342,28 +346,27 @@ static int inflate_disk_obj(git_rawobj *out, git_buf *obj)
 	 * inflate the initial part of the io buffer in order
 	 * to parse the object header (type and size).
 	 */
-	if (start_inflate(&zs, obj, head, sizeof(head)) < Z_OK)
-		return git__throw(GIT_ERROR, "Failed to inflate disk object. Could not inflate buffer");
-
-	if ((used = get_object_header(&hdr, head)) == 0)
-		return git__throw(GIT_ERROR, "Failed to inflate disk object. Object has no header");
-
-	if (!git_object_typeisloose(hdr.type))
-		return git__throw(GIT_ERROR, "Failed to inflate disk object. Wrong object type");
+	if (start_inflate(&zs, obj, head, sizeof(head)) < Z_OK ||
+		(used = get_object_header(&hdr, head)) == 0 ||
+		!git_object_typeisloose(hdr.type))
+	{
+		giterr_set(GITERR_ODB, "Failed to inflate disk object.");
+		return -1;
+	}
 
 	/*
 	 * allocate a buffer and inflate the object data into it
 	 * (including the initial sequence in the head buffer).
 	 */
 	if ((buf = inflate_tail(&zs, head, used, &hdr)) == NULL)
-		return GIT_ENOMEM;
+		return -1;
 	buf[hdr.size] = '\0';
 
 	out->data = buf;
 	out->len = hdr.size;
 	out->type = hdr.type;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
@@ -388,24 +391,23 @@ static int read_loose(git_rawobj *out, git_buf *loc)
 	assert(out && loc);
 
 	if (git_buf_oom(loc))
-		return GIT_ENOMEM;
+		return -1;
 
 	out->data = NULL;
 	out->len = 0;
 	out->type = GIT_OBJ_BAD;
 
-	if (git_futils_readbuffer(&obj, loc->ptr) < 0)
-		return git__throw(GIT_ENOTFOUND, "Failed to read loose object. File not found");
+	if (!(error = git_futils_readbuffer(&obj, loc->ptr)))
+		error = inflate_disk_obj(out, &obj);
 
-	error = inflate_disk_obj(out, &obj);
 	git_buf_free(&obj);
 
-	return error == GIT_SUCCESS ? GIT_SUCCESS : git__rethrow(error, "Failed to read loose object");
+	return error;
 }
 
 static int read_header_loose(git_rawobj *out, git_buf *loc)
 {
-	int error = GIT_SUCCESS, z_return = Z_ERRNO, read_bytes;
+	int error = 0, z_return = Z_ERRNO, read_bytes;
 	git_file fd;
 	z_stream zs;
 	obj_hdr header_obj;
@@ -414,48 +416,40 @@ static int read_header_loose(git_rawobj *out, git_buf *loc)
 	assert(out && loc);
 
 	if (git_buf_oom(loc))
-		return GIT_ENOMEM;
+		return -1;
 
 	out->data = NULL;
 
-	if ((fd = p_open(loc->ptr, O_RDONLY)) < 0)
-		return git__throw(GIT_ENOTFOUND, "Failed to read loose object header. File not found");
+	if ((fd = git_futils_open_ro(loc->ptr)) < 0)
+		return fd;
 
 	init_stream(&zs, inflated_buffer, sizeof(inflated_buffer));
 
-	if (inflateInit(&zs) < Z_OK) {
-		error = GIT_EZLIB;
-		goto cleanup;
-	}
+	z_return = inflateInit(&zs);
 
-	do {
-		if ((read_bytes = read(fd, raw_buffer, sizeof(raw_buffer))) > 0) {
+	while (z_return == Z_OK) {
+		if ((read_bytes = p_read(fd, raw_buffer, sizeof(raw_buffer))) > 0) {
 			set_stream_input(&zs, raw_buffer, read_bytes);
 			z_return = inflate(&zs, 0);
-		} else {
+		} else
 			z_return = Z_STREAM_END;
-			break;
-		}
-	} while (z_return == Z_OK);
+	}
 
 	if ((z_return != Z_STREAM_END && z_return != Z_BUF_ERROR)
 		|| get_object_header(&header_obj, inflated_buffer) == 0
-		|| git_object_typeisloose(header_obj.type) == 0) {
-		error = GIT_EOBJCORRUPTED;
-		goto cleanup;
+		|| git_object_typeisloose(header_obj.type) == 0)
+	{
+		giterr_set(GITERR_ZLIB, "Failed to read loose object header");
+		error = -1;
+	} else {
+		out->len = header_obj.size;
+		out->type = header_obj.type;
 	}
 
-	out->len = header_obj.size;
-	out->type = header_obj.type;
-
-cleanup:
 	finish_inflate(&zs);
 	p_close(fd);
 
-	if (error < GIT_SUCCESS)
-		return git__throw(error, "Failed to read loose object header. Header is corrupted");
-
-	return GIT_SUCCESS;
+	return error;
 }
 
 static int locate_object(
@@ -465,8 +459,8 @@ static int locate_object(
 {
 	int error = object_file_name(object_location, backend->objects_dir, oid);
 
-	if (error == GIT_SUCCESS)
-		error = git_path_exists(git_buf_cstr(object_location)) ? GIT_SUCCESS : GIT_ENOTFOUND;
+	if (!error && !git_path_exists(object_location->ptr))
+		return GIT_ENOTFOUND;
 
 	return error;
 }
@@ -477,7 +471,7 @@ static int fn_locate_object_short_oid(void *state, git_buf *pathbuf) {
 
 	if (pathbuf->size - sstate->dir_len != GIT_OID_HEXSZ - 2) {
 		/* Entry cannot be an object. Continue to next entry */
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	if (git_path_isdir(pathbuf->ptr) == false) {
@@ -495,10 +489,11 @@ static int fn_locate_object_short_oid(void *state, git_buf *pathbuf) {
 			sstate->found++;
 		}
 	}
+
 	if (sstate->found > 1)
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Ambiguous sha1 prefix within loose objects");
+		return git_odb__error_ambiguous("multiple matches in loose objects");
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 /* Locate an object matching a given short oid */
@@ -515,8 +510,8 @@ static int locate_object_short_oid(
 	int error;
 
 	/* prealloc memory for OBJ_DIR/xx/ */
-	if ((error = git_buf_grow(object_location, dir_len + 5)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to locate object from short oid");
+	if (git_buf_grow(object_location, dir_len + 5) < 0)
+		return -1;
 
 	git_buf_sets(object_location, objects_dir);
 	git_path_to_dir(object_location);
@@ -528,46 +523,43 @@ static int locate_object_short_oid(
 	git_oid_fmt((char *)state.short_oid, short_oid);
 
 	/* Explore OBJ_DIR/xx/ where xx is the beginning of hex formatted short oid */
-	error = git_buf_printf(object_location, "%.2s/", state.short_oid);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to locate object from short oid");
+	if (git_buf_printf(object_location, "%.2s/", state.short_oid) < 0)
+		return -1;
 
 	/* Check that directory exists */
 	if (git_path_isdir(object_location->ptr) == false)
-		return git__throw(GIT_ENOTFOUND, "Failed to locate object from short oid. Object not found");
+		return git_odb__error_notfound("failed to locate from short oid");
 
 	state.dir_len = object_location->size;
 	state.short_oid_len = len;
 	state.found = 0;
 
 	/* Explore directory to find a unique object matching short_oid */
-	error = git_path_direach(object_location, fn_locate_object_short_oid, &state);
+	error = git_path_direach(
+		object_location, fn_locate_object_short_oid, &state);
 	if (error)
-		return git__rethrow(error, "Failed to locate object from short oid");
+		return error;
 
-	if (!state.found) {
-		return git__throw(GIT_ENOTFOUND, "Failed to locate object from short oid. Object not found");
-	}
+	if (!state.found)
+		return git_odb__error_notfound("failed to locate from short oid");
 
 	/* Convert obtained hex formatted oid to raw */
 	error = git_oid_fromstr(res_oid, (char *)state.res_oid);
-	if (error) {
-		return git__rethrow(error, "Failed to locate object from short oid");
-	}
+	if (error)
+		return error;
 
 	/* Update the location according to the oid obtained */
 
 	git_buf_truncate(object_location, dir_len);
-	error = git_buf_grow(object_location, dir_len + GIT_OID_HEXSZ + 2);
-	if (error)
-		return git__rethrow(error, "Failed to locate object from short oid");
+	if (git_buf_grow(object_location, dir_len + GIT_OID_HEXSZ + 2) < 0)
+		return -1;
 
 	git_oid_pathfmt(object_location->ptr + dir_len, res_oid);
 
 	object_location->size += GIT_OID_HEXSZ + 1;
 	object_location->ptr[object_location->size] = '\0';
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 
@@ -598,8 +590,8 @@ static int loose_backend__read_header(size_t *len_p, git_otype *type_p, git_odb_
 	raw.type = GIT_OBJ_BAD;
 
 	if (locate_object(&object_path, (loose_backend *)backend, oid) < 0)
-		error = git__throw(GIT_ENOTFOUND, "Failed to read loose backend header. Object not found");
-	else if ((error = read_header_loose(&raw, &object_path)) == GIT_SUCCESS) {
+		error = git_odb__error_notfound("in loose backend");
+	else if ((error = read_header_loose(&raw, &object_path)) == 0) {
 		*len_p = raw.len;
 		*type_p = raw.type;
 	}
@@ -613,20 +605,17 @@ static int loose_backend__read(void **buffer_p, size_t *len_p, git_otype *type_p
 {
 	git_buf object_path = GIT_BUF_INIT;
 	git_rawobj raw;
-	int error = GIT_SUCCESS;
+	int error = 0;
 
 	assert(backend && oid);
 
 	if (locate_object(&object_path, (loose_backend *)backend, oid) < 0)
-		error = git__throw(GIT_ENOTFOUND, "Failed to read loose backend. Object not found");
-	else if ((error = read_loose(&raw, &object_path)) == GIT_SUCCESS) {
+		error = git_odb__error_notfound("in loose backend");
+	else if ((error = read_loose(&raw, &object_path)) == 0) {
 		*buffer_p = raw.data;
 		*len_p = raw.len;
 		*type_p = raw.type;
 	}
-	else {
-		git__rethrow(error, "Failed to read loose backend");
-	}
 
 	git_buf_free(&object_path);
 
@@ -642,16 +631,15 @@ static int loose_backend__read_prefix(
 	const git_oid *short_oid,
 	unsigned int len)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 
 	if (len < GIT_OID_MINPREFIXLEN)
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to read loose "
-			"backend. Prefix length is lower than %d.", GIT_OID_MINPREFIXLEN);
+		error = git_odb__error_ambiguous("prefix length too short");
 
-	if (len >= GIT_OID_HEXSZ) {
+	else if (len >= GIT_OID_HEXSZ) {
 		/* We can fall back to regular read method */
 		error = loose_backend__read(buffer_p, len_p, type_p, backend, short_oid);
-		if (error == GIT_SUCCESS)
+		if (!error)
 			git_oid_cpy(out_oid, short_oid);
 	} else {
 		git_buf object_path = GIT_BUF_INIT;
@@ -660,11 +648,9 @@ static int loose_backend__read_prefix(
 		assert(backend && short_oid);
 
 		if ((error = locate_object_short_oid(&object_path, out_oid,
-		    (loose_backend *)backend, short_oid, len)) < 0)
-			git__rethrow(error, "Failed to read loose backend");
-		else if ((error = read_loose(&raw, &object_path)) < GIT_SUCCESS)
-			git__rethrow(error, "Failed to read loose backend");
-		else {
+				(loose_backend *)backend, short_oid, len)) == 0 &&
+			(error = read_loose(&raw, &object_path)) == 0)
+		{
 			*buffer_p = raw.data;
 			*len_p = raw.len;
 			*type_p = raw.type;
@@ -687,47 +673,33 @@ static int loose_backend__exists(git_odb_backend *backend, const git_oid *oid)
 
 	git_buf_free(&object_path);
 
-	return (error == GIT_SUCCESS);
+	return !error;
 }
 
 static int loose_backend__stream_fwrite(git_oid *oid, git_odb_stream *_stream)
 {
 	loose_writestream *stream = (loose_writestream *)_stream;
 	loose_backend *backend = (loose_backend *)_stream->backend;
-
-	int error;
 	git_buf final_path = GIT_BUF_INIT;
+	int error = 0;
 
-	if ((error = git_filebuf_hash(oid, &stream->fbuf)) < GIT_SUCCESS)
-		goto cleanup;
-
-	if ((error = object_file_name(&final_path, backend->objects_dir, oid)) < GIT_SUCCESS)
-		goto cleanup;
-
-	if (git_buf_oom(&final_path))
-		return GIT_ENOMEM;
-
-	if ((error = git_futils_mkpath2file(final_path.ptr, GIT_OBJECT_DIR_MODE)) < GIT_SUCCESS)
-		goto cleanup;
-
+	if (git_filebuf_hash(oid, &stream->fbuf) < 0 ||
+		object_file_name(&final_path, backend->objects_dir, oid) < 0 ||
+		git_futils_mkpath2file(final_path.ptr, GIT_OBJECT_DIR_MODE) < 0)
+		error = -1;
 	/*
 	 * Don't try to add an existing object to the repository. This
 	 * is what git does and allows us to sidestep the fact that
 	 * we're not allowed to overwrite a read-only file on Windows.
 	 */
-	if (git_path_exists(final_path.ptr) == true) {
+	else if (git_path_exists(final_path.ptr) == true)
 		git_filebuf_cleanup(&stream->fbuf);
-		goto cleanup;
-	}
-
-	error = git_filebuf_commit_at(&stream->fbuf, final_path.ptr, GIT_OBJECT_FILE_MODE);
+	else
+		error = git_filebuf_commit_at(
+			&stream->fbuf, final_path.ptr, GIT_OBJECT_FILE_MODE);
 
-cleanup:
 	git_buf_free(&final_path);
 
-	if (error < GIT_SUCCESS)
-		git__rethrow(error, "Failed to write loose backend");
-
 	return error;
 }
 
@@ -751,22 +723,18 @@ static int format_object_header(char *hdr, size_t n, size_t obj_len, git_otype o
 	int len = snprintf(hdr, n, "%s %"PRIuZ, type_str, obj_len);
 
 	assert(len > 0);				/* otherwise snprintf() is broken */
-	assert(((size_t) len) < n); /* otherwise the caller is broken! */
+	assert(((size_t)len) < n);		/* otherwise the caller is broken! */
 
-	if (len < 0 || ((size_t) len) >= n)
-		return git__throw(GIT_ERROR, "Failed to format object header. Length is out of bounds");
 	return len+1;
 }
 
 static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_backend, size_t length, git_otype type)
 {
 	loose_backend *backend;
-	loose_writestream *stream;
-
+	loose_writestream *stream = NULL;
 	char hdr[64];
 	git_buf tmp_path = GIT_BUF_INIT;
 	int hdrlen;
-	int error;
 
 	assert(_backend);
 
@@ -774,12 +742,9 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 	*stream_out = NULL;
 
 	hdrlen = format_object_header(hdr, sizeof(hdr), length, type);
-	if (hdrlen < GIT_SUCCESS)
-		return git__throw(GIT_EOBJCORRUPTED, "Failed to create loose backend stream. Object is corrupted");
 
 	stream = git__calloc(1, sizeof(loose_writestream));
-	if (stream == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(stream);
 
 	stream->stream.backend = _backend;
 	stream->stream.read = NULL; /* read only */
@@ -788,31 +753,21 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 	stream->stream.free = &loose_backend__stream_free;
 	stream->stream.mode = GIT_STREAM_WRONLY;
 
-	error = git_buf_joinpath(&tmp_path, backend->objects_dir, "tmp_object");
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
-	error = git_filebuf_open(&stream->fbuf, tmp_path.ptr,
-		GIT_FILEBUF_HASH_CONTENTS |
-		GIT_FILEBUF_TEMPORARY |
-		(backend->object_zlib_level << GIT_FILEBUF_DEFLATE_SHIFT));
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
-	error = stream->stream.write((git_odb_stream *)stream, hdr, hdrlen);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
+	if (git_buf_joinpath(&tmp_path, backend->objects_dir, "tmp_object") < 0 ||
+		git_filebuf_open(&stream->fbuf, tmp_path.ptr,
+			GIT_FILEBUF_HASH_CONTENTS |
+			GIT_FILEBUF_TEMPORARY |
+			(backend->object_zlib_level << GIT_FILEBUF_DEFLATE_SHIFT)) < 0 ||
+		stream->stream.write((git_odb_stream *)stream, hdr, hdrlen) < 0)
+	{
+		git_filebuf_cleanup(&stream->fbuf);
+		git__free(stream);
+		stream = NULL;
+	}
 	git_buf_free(&tmp_path);
-
 	*stream_out = (git_odb_stream *)stream;
-	return GIT_SUCCESS;
 
-cleanup:
-	git_buf_free(&tmp_path);
-	git_filebuf_cleanup(&stream->fbuf);
-	git__free(stream);
-	return git__rethrow(error, "Failed to create loose backend stream");
+	return !stream ? -1 : 0;
 }
 
 static int loose_backend__write(git_oid *oid, git_odb_backend *_backend, const void *data, size_t len, git_otype type)
@@ -826,36 +781,26 @@ static int loose_backend__write(git_oid *oid, git_odb_backend *_backend, const v
 	backend = (loose_backend *)_backend;
 
 	/* prepare the header for the file */
-	{
-		header_len = format_object_header(header, sizeof(header), len, type);
-		if (header_len < GIT_SUCCESS)
-			return GIT_EOBJCORRUPTED;
-	}
-
-	error = git_buf_joinpath(&final_path, backend->objects_dir, "tmp_object");
-	if (error < GIT_SUCCESS)
-		goto cleanup;
+	header_len = format_object_header(header, sizeof(header), len, type);
 
-	error = git_filebuf_open(&fbuf, final_path.ptr,
-		GIT_FILEBUF_HASH_CONTENTS |
-		GIT_FILEBUF_TEMPORARY |
-		(backend->object_zlib_level << GIT_FILEBUF_DEFLATE_SHIFT));
-	if (error < GIT_SUCCESS)
+	if (git_buf_joinpath(&final_path, backend->objects_dir, "tmp_object") < 0 ||
+		git_filebuf_open(&fbuf, final_path.ptr,
+			GIT_FILEBUF_HASH_CONTENTS |
+			GIT_FILEBUF_TEMPORARY |
+			(backend->object_zlib_level << GIT_FILEBUF_DEFLATE_SHIFT)) < 0)
+	{
+		error = -1;
 		goto cleanup;
+	}
 
 	git_filebuf_write(&fbuf, header, header_len);
 	git_filebuf_write(&fbuf, data, len);
 	git_filebuf_hash(oid, &fbuf);
 
-	error = object_file_name(&final_path, backend->objects_dir, oid);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
-	error = git_futils_mkpath2file(final_path.ptr, GIT_OBJECT_DIR_MODE);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
-
-	error = git_filebuf_commit_at(&fbuf, final_path.ptr, GIT_OBJECT_FILE_MODE);
+	if (object_file_name(&final_path, backend->objects_dir, oid) < 0 ||
+		git_futils_mkpath2file(final_path.ptr, GIT_OBJECT_DIR_MODE) < 0 ||
+		git_filebuf_commit_at(&fbuf, final_path.ptr, GIT_OBJECT_FILE_MODE) < 0)
+		error = -1;
 
 cleanup:
 	if (error < GIT_SUCCESS)
@@ -883,14 +828,10 @@ int git_odb_backend_loose(
 	loose_backend *backend;
 
 	backend = git__calloc(1, sizeof(loose_backend));
-	if (backend == NULL)
-		return GIT_ENOMEM;
+	GITERR_CHECK_ALLOC(backend);
 
 	backend->objects_dir = git__strdup(objects_dir);
-	if (backend->objects_dir == NULL) {
-		git__free(backend);
-		return GIT_ENOMEM;
-	}
+	GITERR_CHECK_ALLOC(backend->objects_dir);
 
 	if (compression_level < 0)
 		compression_level = Z_BEST_SPEED;
@@ -907,5 +848,5 @@ int git_odb_backend_loose(
 	backend->parent.free = &loose_backend__free;
 
 	*backend_out = (git_odb_backend *)backend;
-	return GIT_SUCCESS;
+	return 0;
 }
diff --git a/src/odb_pack.c b/src/odb_pack.c
index 159c886..7add371 100644
--- a/src/odb_pack.c
+++ b/src/odb_pack.c
@@ -137,19 +137,19 @@ static int packfile_load__cb(void *_data, git_buf *path);
 static int packfile_refresh_all(struct pack_backend *backend);
 
 static int pack_entry_find(struct git_pack_entry *e,
-		struct pack_backend *backend, const git_oid *oid);
+	struct pack_backend *backend, const git_oid *oid);
 
 /* Can find the offset of an object given
  * a prefix of an identifier.
- * Throws GIT_EAMBIGUOUSOIDPREFIX if short oid
- * is ambiguous.
+ * Sets GIT_EAMBIGUOUS if short oid is ambiguous.
  * This method assumes that len is between
  * GIT_OID_MINPREFIXLEN and GIT_OID_HEXSZ.
  */
-static int pack_entry_find_prefix(struct git_pack_entry *e,
-					struct pack_backend *backend,
-					const git_oid *short_oid,
-					unsigned int len);
+static int pack_entry_find_prefix(
+	struct git_pack_entry *e,
+	struct pack_backend *backend,
+	const git_oid *short_oid,
+	unsigned int len);
 
 
 
@@ -215,27 +215,22 @@ static int packfile_load__cb(void *_data, git_buf *path)
 	size_t i;
 
 	if (git__suffixcmp(path->ptr, ".idx") != 0)
-		return GIT_SUCCESS; /* not an index */
+		return 0; /* not an index */
 
 	for (i = 0; i < backend->packs.length; ++i) {
 		struct git_pack_file *p = git_vector_get(&backend->packs, i);
 		if (memcmp(p->pack_name, path->ptr, path->size - strlen(".idx")) == 0)
-			return GIT_SUCCESS;
+			return 0;
 	}
 
 	error = git_packfile_check(&pack, path->ptr);
-	if (error == GIT_ENOTFOUND) {
+	if (error == GIT_ENOTFOUND)
 		/* ignore missing .pack file as git does */
 		return GIT_SUCCESS;
-	} else if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to load packfile");
-
-	if (git_vector_insert(&backend->packs, pack) < GIT_SUCCESS) {
-		git__free(pack);
-		return GIT_ENOMEM;
-	}
+	else if (error < 0)
+		return error;
 
-	return GIT_SUCCESS;
+	return git_vector_insert(&backend->packs, pack);
 }
 
 static int packfile_refresh_all(struct pack_backend *backend)
@@ -244,10 +239,10 @@ static int packfile_refresh_all(struct pack_backend *backend)
 	struct stat st;
 
 	if (backend->pack_folder == NULL)
-		return GIT_SUCCESS;
+		return 0;
 
 	if (p_stat(backend->pack_folder, &st) < 0 || !S_ISDIR(st.st_mode))
-		return git__throw(GIT_ENOTFOUND, "Failed to refresh packfiles. Backend not found");
+		return git_odb__error_notfound("failed to refresh packfiles");
 
 	if (st.st_mtime != backend->pack_folder_mtime) {
 		git_buf path = GIT_BUF_INIT;
@@ -257,14 +252,15 @@ static int packfile_refresh_all(struct pack_backend *backend)
 		error = git_path_direach(&path, packfile_load__cb, (void *)backend);
 
 		git_buf_free(&path);
-		if (error < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to refresh packfiles");
+
+		if (error < 0)
+			return error;
 
 		git_vector_sort(&backend->packs);
 		backend->pack_folder_mtime = st.st_mtime;
 	}
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int pack_entry_find(struct git_pack_entry *e, struct pack_backend *backend, const git_oid *oid)
@@ -272,12 +268,12 @@ static int pack_entry_find(struct git_pack_entry *e, struct pack_backend *backen
 	int error;
 	size_t i;
 
-	if ((error = packfile_refresh_all(backend)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to find pack entry");
+	if ((error = packfile_refresh_all(backend)) < 0)
+		return error;
 
 	if (backend->last_found &&
-		git_pack_entry_find(e, backend->last_found, oid, GIT_OID_HEXSZ) == GIT_SUCCESS)
-		return GIT_SUCCESS;
+		git_pack_entry_find(e, backend->last_found, oid, GIT_OID_HEXSZ) == 0)
+		return 0;
 
 	for (i = 0; i < backend->packs.length; ++i) {
 		struct git_pack_file *p;
@@ -286,13 +282,13 @@ static int pack_entry_find(struct git_pack_entry *e, struct pack_backend *backen
 		if (p == backend->last_found)
 			continue;
 
-		if (git_pack_entry_find(e, p, oid, GIT_OID_HEXSZ) == GIT_SUCCESS) {
+		if (git_pack_entry_find(e, p, oid, GIT_OID_HEXSZ) == 0) {
 			backend->last_found = p;
-			return GIT_SUCCESS;
+			return 0;
 		}
 	}
 
-	return git__throw(GIT_ENOTFOUND, "Failed to find pack entry");
+	return git_odb__error_notfound("failed to find pack entry");
 }
 
 static int pack_entry_find_prefix(
@@ -305,16 +301,15 @@ static int pack_entry_find_prefix(
 	size_t i;
 	unsigned found = 0;
 
-	if ((error = packfile_refresh_all(backend)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to find pack entry");
+	if ((error = packfile_refresh_all(backend)) < 0)
+		return error;
 
 	if (backend->last_found) {
 		error = git_pack_entry_find(e, backend->last_found, short_oid, len);
-		if (error == GIT_EAMBIGUOUSOIDPREFIX) {
-			return git__rethrow(error, "Failed to find pack entry. Ambiguous sha1 prefix");
-		} else if (error == GIT_SUCCESS) {
+		if (error == GIT_EAMBIGUOUS)
+			return error;
+		if (!error)
 			found = 1;
-		}
 	}
 
 	for (i = 0; i < backend->packs.length; ++i) {
@@ -325,24 +320,21 @@ static int pack_entry_find_prefix(
 			continue;
 
 		error = git_pack_entry_find(e, p, short_oid, len);
-		if (error == GIT_EAMBIGUOUSOIDPREFIX) {
-			return git__rethrow(error, "Failed to find pack entry. Ambiguous sha1 prefix");
-		} else if (error == GIT_SUCCESS) {
-			found++;
-			if (found > 1)
+		if (error == GIT_EAMBIGUOUS)
+			return error;
+		if (!error) {
+			if (++found > 1)
 				break;
 			backend->last_found = p;
 		}
 	}
 
-	if (!found) {
-		return git__rethrow(GIT_ENOTFOUND, "Failed to find pack entry");
-	} else if (found > 1) {
-		return git__rethrow(GIT_EAMBIGUOUSOIDPREFIX, "Failed to find pack entry. Ambiguous sha1 prefix");
-	} else {
-		return GIT_SUCCESS;
-	}
-
+	if (!found)
+		return git_odb__error_notfound("failed to find pack entry");
+	else if (found > 1)
+		return git_odb__error_ambiguous("found multiple pack entries");
+	else
+		return 0;
 }
 
 
@@ -374,17 +366,15 @@ static int pack_backend__read(void **buffer_p, size_t *len_p, git_otype *type_p,
 	git_rawobj raw;
 	int error;
 
-	if ((error = pack_entry_find(&e, (struct pack_backend *)backend, oid)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to read pack backend");
-
-	if ((error = git_packfile_unpack(&raw, e.p, &e.offset)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to read pack backend");
+	if ((error = pack_entry_find(&e, (struct pack_backend *)backend, oid)) < 0 ||
+		(error = git_packfile_unpack(&raw, e.p, &e.offset)) < 0)
+		return error;
 
 	*buffer_p = raw.data;
 	*len_p = raw.len;
 	*type_p = raw.type;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int pack_backend__read_prefix(
@@ -396,40 +386,38 @@ static int pack_backend__read_prefix(
 	const git_oid *short_oid,
 	unsigned int len)
 {
+	int error = 0;
+
 	if (len < GIT_OID_MINPREFIXLEN)
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to read pack backend. Prefix length is lower than %d.", GIT_OID_MINPREFIXLEN);
+		error = git_odb__error_ambiguous("prefix length too short");
 
-	if (len >= GIT_OID_HEXSZ) {
+	else if (len >= GIT_OID_HEXSZ) {
 		/* We can fall back to regular read method */
-		int error = pack_backend__read(buffer_p, len_p, type_p, backend, short_oid);
-		if (error == GIT_SUCCESS)
+		error = pack_backend__read(buffer_p, len_p, type_p, backend, short_oid);
+		if (!error)
 			git_oid_cpy(out_oid, short_oid);
-
-		return error;
 	} else {
 		struct git_pack_entry e;
 		git_rawobj raw;
-		int error;
-
-		if ((error = pack_entry_find_prefix(&e, (struct pack_backend *)backend, short_oid, len)) < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to read pack backend");
 
-		if ((error = git_packfile_unpack(&raw, e.p, &e.offset)) < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to read pack backend");
-
-		*buffer_p = raw.data;
-		*len_p = raw.len;
-		*type_p = raw.type;
-		git_oid_cpy(out_oid, &e.sha1);
+		if ((error = pack_entry_find_prefix(
+				&e, (struct pack_backend *)backend, short_oid, len)) == 0 &&
+			(error = git_packfile_unpack(&raw, e.p, &e.offset)) == 0)
+		{
+			*buffer_p = raw.data;
+			*len_p = raw.len;
+			*type_p = raw.type;
+			git_oid_cpy(out_oid, &e.sha1);
+		}
 	}
 
-	return GIT_SUCCESS;
+	return error;
 }
 
 static int pack_backend__exists(git_odb_backend *backend, const git_oid *oid)
 {
 	struct git_pack_entry e;
-	return pack_entry_find(&e, (struct pack_backend *)backend, oid) == GIT_SUCCESS;
+	return pack_entry_find(&e, (struct pack_backend *)backend, oid) == 0;
 }
 
 static void pack_backend__free(git_odb_backend *_backend)
@@ -455,19 +443,16 @@ int git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir)
 {
 	struct pack_backend *backend = NULL;
 	git_buf path = GIT_BUF_INIT;
-	int error = GIT_SUCCESS;
 
 	backend = git__calloc(1, sizeof(struct pack_backend));
-	if (backend == NULL)
-		return GIT_ENOMEM;
-
-	error = git_vector_init(&backend->packs, 8, packfile_sort__cb);
-	if (error < GIT_SUCCESS)
-		goto cleanup;
+	GITERR_CHECK_ALLOC(backend);
 
-	error = git_buf_joinpath(&path, objects_dir, "pack");
-	if (error < GIT_SUCCESS)
-		goto cleanup;
+	if (git_vector_init(&backend->packs, 8, packfile_sort__cb) < 0 ||
+		git_buf_joinpath(&path, objects_dir, "pack") < 0)
+	{
+		git__free(backend);
+		return -1;
+	}
 
 	if (git_path_isdir(git_buf_cstr(&path)) == true) {
 		backend->pack_folder = git_buf_detach(&path);
@@ -482,10 +467,7 @@ int git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir)
 
 	*backend_out = (git_odb_backend *)backend;
 
-cleanup:
-	if (error < GIT_SUCCESS)
-		git__free(backend);
 	git_buf_free(&path);
 
-	return error;
+	return 0;
 }
diff --git a/src/pack.c b/src/pack.c
index acab873..40b3ca7 100644
--- a/src/pack.c
+++ b/src/pack.c
@@ -17,12 +17,12 @@
 #include <zlib.h>
 
 static int packfile_open(struct git_pack_file *p);
-static off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n);
+static git_off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n);
 int packfile_unpack_compressed(
 		git_rawobj *obj,
 		struct git_pack_file *p,
 		git_mwindow **w_curs,
-		off_t *curpos,
+		git_off_t *curpos,
 		size_t size,
 		git_otype type);
 
@@ -34,12 +34,18 @@ int packfile_unpack_compressed(
  * GIT_OID_MINPREFIXLEN and GIT_OID_HEXSZ.
  */
 static int pack_entry_find_offset(
-		off_t *offset_out,
+		git_off_t *offset_out,
 		git_oid *found_oid,
 		struct git_pack_file *p,
 		const git_oid *short_oid,
 		unsigned int len);
 
+static int packfile_error(const char *message)
+{
+	giterr_set(GITERR_ODB, "Invalid pack file - %s", message);
+	return -1;
+}
+
 /***********************************************************
  *
  * PACK INDEX METHODS
@@ -58,40 +64,31 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 {
 	struct git_pack_idx_header *hdr;
 	uint32_t version, nr, i, *index;
-
 	void *idx_map;
 	size_t idx_size;
-
 	struct stat st;
-
-	/* TODO: properly open the file without access time */
-	git_file fd = p_open(path, O_RDONLY /*| O_NOATIME */);
-
 	int error;
-
+	/* TODO: properly open the file without access time using O_NOATIME */
+	git_file fd = git_futils_open_ro(path);
 	if (fd < 0)
-		return git__throw(GIT_EOSERR, "Failed to check index. File missing or corrupted");
+		return fd;
 
-	if (p_fstat(fd, &st) < GIT_SUCCESS) {
+	if (p_fstat(fd, &st) < 0 ||
+		!S_ISREG(st.st_mode) ||
+		!git__is_sizet(st.st_size) ||
+		(idx_size = (size_t)st.st_size) < 4 * 256 + 20 + 20)
+	{
 		p_close(fd);
-		return git__throw(GIT_EOSERR, "Failed to check index. File appears to be corrupted");
-	}
-
-	if (!git__is_sizet(st.st_size))
-		return GIT_ENOMEM;
-
-	idx_size = (size_t)st.st_size;
-
-	if (idx_size < 4 * 256 + 20 + 20) {
-		p_close(fd);
-		return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Object is corrupted");
+		giterr_set(GITERR_OS, "Failed to check pack index.");
+		return -1;
 	}
 
 	error = git_futils_mmap_ro(&p->index_map, fd, 0, idx_size);
+
 	p_close(fd);
 
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to check index");
+	if (error < 0)
+		return error;
 
 	hdr = idx_map = p->index_map.data;
 
@@ -100,7 +97,7 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 
 		if (version < 2 || version > 2) {
 			git_futils_mmap_free(&p->index_map);
-			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Unsupported index version");
+			return packfile_error("unsupported index version");
 		}
 
 	} else
@@ -116,7 +113,7 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 		uint32_t n = ntohl(index[i]);
 		if (n < nr) {
 			git_futils_mmap_free(&p->index_map);
-			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Index is non-monotonic");
+			return packfile_error("index is non-monotonic");
 		}
 		nr = n;
 	}
@@ -131,7 +128,7 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 		 */
 		if (idx_size != 4*256 + nr * 24 + 20 + 20) {
 			git_futils_mmap_free(&p->index_map);
-			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Object is corrupted");
+			return packfile_error("index is corrupted");
 		}
 	} else if (version == 2) {
 		/*
@@ -155,13 +152,13 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 
 		if (idx_size < min_size || idx_size > max_size) {
 			git_futils_mmap_free(&p->index_map);
-			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Wrong index size");
+			return packfile_error("wrong index size");
 		}
 	}
 
 	p->index_version = version;
 	p->num_objects = nr;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int pack_index_open(struct git_pack_file *p)
@@ -170,24 +167,26 @@ static int pack_index_open(struct git_pack_file *p)
 	int error;
 
 	if (p->index_map.data)
-		return GIT_SUCCESS;
+		return 0;
 
 	idx_name = git__strdup(p->pack_name);
+	GITERR_CHECK_ALLOC(idx_name);
+
 	strcpy(idx_name + strlen(idx_name) - strlen(".pack"), ".idx");
 
 	error = pack_index_check(idx_name, p);
 	git__free(idx_name);
 
-	return error == GIT_SUCCESS ? GIT_SUCCESS : git__rethrow(error, "Failed to open index");
+	return error;
 }
 
 static unsigned char *pack_window_open(
 		struct git_pack_file *p,
 		git_mwindow **w_cursor,
-		off_t offset,
+		git_off_t offset,
 		unsigned int *left)
 {
-	if (p->mwf.fd == -1 && packfile_open(p) < GIT_SUCCESS)
+	if (p->mwf.fd == -1 && packfile_open(p) < 0)
 		return NULL;
 
 	/* Since packfiles end in a hash of their content and it's
@@ -233,7 +232,7 @@ int git_packfile_unpack_header(
 		git_otype *type_p,
 		git_mwindow_file *mwf,
 		git_mwindow **w_curs,
-		off_t *curpos)
+		git_off_t *curpos)
 {
 	unsigned char *base;
 	unsigned int left;
@@ -248,35 +247,34 @@ int git_packfile_unpack_header(
 //	base = pack_window_open(p, w_curs, *curpos, &left);
 	base = git_mwindow_open(mwf, w_curs, *curpos, 20, &left);
 	if (base == NULL)
-		return GIT_ENOMEM;
+		return -1;
 
 	used = packfile_unpack_header1(size_p, type_p, base, left);
-
 	if (used == 0)
-		return git__throw(GIT_EOBJCORRUPTED, "Header length is zero");
+		return packfile_error("header length is zero");
 
 	*curpos += used;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 static int packfile_unpack_delta(
 		git_rawobj *obj,
 		struct git_pack_file *p,
 		git_mwindow **w_curs,
-		off_t *curpos,
+		git_off_t *curpos,
 		size_t delta_size,
 		git_otype delta_type,
-		off_t obj_offset)
+		git_off_t obj_offset)
 {
-	off_t base_offset;
+	git_off_t base_offset;
 	git_rawobj base, delta;
 	int error;
 
 	base_offset = get_delta_base(p, w_curs, curpos, delta_type, obj_offset);
 	if (base_offset == 0)
-		return git__throw(GIT_EOBJCORRUPTED, "Delta offset is zero");
-	if (base_offset < 0)
-		return git__rethrow(base_offset, "Failed to get delta base");
+		return packfile_error("delta offset is zero");
+	if (base_offset < 0) /* must actually be an error code */
+		return (int)base_offset;
 
 	git_mwindow_close(w_curs);
 	error = git_packfile_unpack(&base, p, &base_offset);
@@ -287,35 +285,34 @@ static int packfile_unpack_delta(
 	 *
 	 * We'll need to do this in order to support thin packs.
 	 */
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Corrupted delta");
+	if (error < 0)
+		return error;
 
 	error = packfile_unpack_compressed(&delta, p, w_curs, curpos, delta_size, delta_type);
-	if (error < GIT_SUCCESS) {
+	if (error < 0) {
 		git__free(base.data);
-		return git__rethrow(error, "Corrupted delta");
+		return error;
 	}
 
 	obj->type = base.type;
-	error = git__delta_apply(obj,
-			base.data, base.len,
-			delta.data, delta.len);
+	error = git__delta_apply(obj, base.data, base.len, delta.data, delta.len);
 
 	git__free(base.data);
 	git__free(delta.data);
 
 	/* TODO: we might want to cache this shit. eventually */
 	//add_delta_base_cache(p, base_offset, base, base_size, *type);
+
 	return error; /* error set by git__delta_apply */
 }
 
 int git_packfile_unpack(
-		git_rawobj *obj,
-		struct git_pack_file *p,
-		off_t *obj_offset)
+	git_rawobj *obj,
+	struct git_pack_file *p,
+	git_off_t *obj_offset)
 {
 	git_mwindow *w_curs = NULL;
-	off_t curpos = *obj_offset;
+	git_off_t curpos = *obj_offset;
 	int error;
 
 	size_t size = 0;
@@ -330,8 +327,8 @@ int git_packfile_unpack(
 	obj->type = GIT_OBJ_BAD;
 
 	error = git_packfile_unpack_header(&size, &type, &p->mwf, &w_curs, &curpos);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to unpack packfile");
+	if (error < 0)
+		return error;
 
 	switch (type) {
 	case GIT_OBJ_OFS_DELTA:
@@ -351,33 +348,30 @@ int git_packfile_unpack(
 		break;
 
 	default:
-		error = GIT_EOBJCORRUPTED;
+		error = packfile_error("invalid packfile type in header");;
 		break;
 	}
 
 	git_mwindow_close(&w_curs);
 
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to unpack object");
-
 	*obj_offset = curpos;
-	return GIT_SUCCESS;
+	return error;
 }
 
 int packfile_unpack_compressed(
-		git_rawobj *obj,
-		struct git_pack_file *p,
-		git_mwindow **w_curs,
-		off_t *curpos,
-		size_t size,
-		git_otype type)
+	git_rawobj *obj,
+	struct git_pack_file *p,
+	git_mwindow **w_curs,
+	git_off_t *curpos,
+	size_t size,
+	git_otype type)
 {
 	int st;
 	z_stream stream;
 	unsigned char *buffer, *in;
 
-	buffer = git__malloc(size + 1);
-	memset(buffer, 0x0, size + 1);
+	buffer = git__calloc(1, size + 1);
+	GITERR_CHECK_ALLOC(buffer);
 
 	memset(&stream, 0, sizeof(stream));
 	stream.next_out = buffer;
@@ -386,7 +380,8 @@ int packfile_unpack_compressed(
 	st = inflateInit(&stream);
 	if (st != Z_OK) {
 		git__free(buffer);
-		return git__throw(GIT_EZLIB, "Error in zlib");
+		giterr_set(GITERR_ZLIB, "Failed to inflate packfile");
+		return -1;
 	}
 
 	do {
@@ -404,28 +399,29 @@ int packfile_unpack_compressed(
 
 	if ((st != Z_STREAM_END) || stream.total_out != size) {
 		git__free(buffer);
-		return git__throw(GIT_EZLIB, "Error in zlib");
+		giterr_set(GITERR_ZLIB, "Failed to inflate packfile");
+		return -1;
 	}
 
 	obj->type = type;
 	obj->len = size;
 	obj->data = buffer;
-	return GIT_SUCCESS;
+	return 0;
 }
 
 /*
  * curpos is where the data starts, delta_obj_offset is the where the
  * header starts
  */
-off_t get_delta_base(
-		struct git_pack_file *p,
-		git_mwindow **w_curs,
-		off_t *curpos,
-		git_otype type,
-		off_t delta_obj_offset)
+git_off_t get_delta_base(
+	struct git_pack_file *p,
+	git_mwindow **w_curs,
+	git_off_t *curpos,
+	git_otype type,
+	git_off_t delta_obj_offset)
 {
 	unsigned char *base_info = pack_window_open(p, w_curs, *curpos, NULL);
-	off_t base_offset;
+	git_off_t base_offset;
 	git_oid unused;
 
 	/* pack_window_open() assured us we have [base_info, base_info + 20)
@@ -463,8 +459,8 @@ off_t get_delta_base(
 			}
 		}
 		/* The base entry _must_ be in the same pack */
-		if (pack_entry_find_offset(&base_offset, &unused, p, (git_oid *)base_info, GIT_OID_HEXSZ) < GIT_SUCCESS)
-			return git__rethrow(GIT_EPACKCORRUPTED, "Base entry delta is not in the same pack");
+		if (pack_entry_find_offset(&base_offset, &unused, p, (git_oid *)base_info, GIT_OID_HEXSZ) < 0)
+			return packfile_error("base entry delta is not in the same pack");
 		*curpos += 20;
 	} else
 		return 0;
@@ -480,9 +476,9 @@ off_t get_delta_base(
 
 static struct git_pack_file *packfile_alloc(int extra)
 {
-	struct git_pack_file *p = git__malloc(sizeof(*p) + extra);
-	memset(p, 0, sizeof(*p));
-	p->mwf.fd = -1;
+	struct git_pack_file *p = git__calloc(1, sizeof(*p) + extra);
+	if (p != NULL)
+		p->mwf.fd = -1;
 	return p;
 }
 
@@ -510,24 +506,25 @@ static int packfile_open(struct git_pack_file *p)
 	git_oid sha1;
 	unsigned char *idx_sha1;
 
+	assert(p->index_map.data);
+
 	if (!p->index_map.data && pack_index_open(p) < GIT_SUCCESS)
-		return git__throw(GIT_ENOTFOUND, "Failed to open packfile. File not found");
+		return git_odb__error_notfound("failed to open packfile");
 
 	/* TODO: open with noatime */
-	p->mwf.fd = p_open(p->pack_name, O_RDONLY);
-	if (p->mwf.fd < 0 || p_fstat(p->mwf.fd, &st) < GIT_SUCCESS)
-		return git__throw(GIT_EOSERR, "Failed to open packfile. File appears to be corrupted");
+	p->mwf.fd = git_futils_open_ro(p->pack_name);
+	if (p->mwf.fd < 0)
+		return p->mwf.fd;
 
-	if (git_mwindow_file_register(&p->mwf) < GIT_SUCCESS) {
-		p_close(p->mwf.fd);
-		return git__throw(GIT_ERROR, "Failed to register packfile windows");
-	}
+	if (p_fstat(p->mwf.fd, &st) < 0 ||
+		git_mwindow_file_register(&p->mwf) < 0)
+		goto cleanup;
 
 	/* If we created the struct before we had the pack we lack size. */
 	if (!p->mwf.size) {
 		if (!S_ISREG(st.st_mode))
 			goto cleanup;
-		p->mwf.size = (off_t)st.st_size;
+		p->mwf.size = (git_off_t)st.st_size;
 	} else if (p->mwf.size != st.st_size)
 		goto cleanup;
 
@@ -537,44 +534,35 @@ static int packfile_open(struct git_pack_file *p)
 	 */
 	fd_flag = fcntl(p->mwf.fd, F_GETFD, 0);
 	if (fd_flag < 0)
-		return error("cannot determine file descriptor flags");
+		goto cleanup;
 
 	fd_flag |= FD_CLOEXEC;
 	if (fcntl(p->pack_fd, F_SETFD, fd_flag) == -1)
-		return GIT_EOSERR;
+		goto cleanup;
 #endif
 
 	/* Verify we recognize this pack file format. */
-	if (p_read(p->mwf.fd, &hdr, sizeof(hdr)) < GIT_SUCCESS)
-		goto cleanup;
-
-	if (hdr.hdr_signature != htonl(PACK_SIGNATURE))
-		goto cleanup;
-
-	if (!pack_version_ok(hdr.hdr_version))
+	if (p_read(p->mwf.fd, &hdr, sizeof(hdr)) < 0 ||
+		hdr.hdr_signature != htonl(PACK_SIGNATURE) ||
+		!pack_version_ok(hdr.hdr_version))
 		goto cleanup;
 
 	/* Verify the pack matches its index. */
-	if (p->num_objects != ntohl(hdr.hdr_entries))
-		goto cleanup;
-
-	if (p_lseek(p->mwf.fd, p->mwf.size - GIT_OID_RAWSZ, SEEK_SET) == -1)
-		goto cleanup;
-
-	if (p_read(p->mwf.fd, sha1.id, GIT_OID_RAWSZ) < GIT_SUCCESS)
+	if (p->num_objects != ntohl(hdr.hdr_entries) ||
+		p_lseek(p->mwf.fd, p->mwf.size - GIT_OID_RAWSZ, SEEK_SET) == -1 ||
+		p_read(p->mwf.fd, sha1.id, GIT_OID_RAWSZ) < 0)
 		goto cleanup;
 
 	idx_sha1 = ((unsigned char *)p->index_map.data) + p->index_map.len - 40;
 
-	if (git_oid_cmp(&sha1, (git_oid *)idx_sha1) != 0)
-		goto cleanup;
-
-	return GIT_SUCCESS;
+	if (git_oid_cmp(&sha1, (git_oid *)idx_sha1) == 0)
+		return 0;
 
 cleanup:
+	giterr_set(GITERR_OS, "Invalid packfile '%s'", p->pack_name);
 	p_close(p->mwf.fd);
 	p->mwf.fd = -1;
-	return git__throw(GIT_EPACKCORRUPTED, "Failed to open packfile. Pack is corrupted");
+	return -1;
 }
 
 int git_packfile_check(struct git_pack_file **pack_out, const char *path)
@@ -586,6 +574,7 @@ int git_packfile_check(struct git_pack_file **pack_out, const char *path)
 	*pack_out = NULL;
 	path_len = strlen(path);
 	p = packfile_alloc(path_len + 2);
+	GITERR_CHECK_ALLOC(p);
 
 	/*
 	 * Make sure a corresponding .pack file exists and that
@@ -594,7 +583,7 @@ int git_packfile_check(struct git_pack_file **pack_out, const char *path)
 	path_len -= strlen(".idx");
 	if (path_len < 1) {
 		git__free(p);
-		return git__throw(GIT_ENOTFOUND, "Failed to check packfile. Wrong path name");
+		return git_odb__error_notfound("invalid packfile path");
 	}
 
 	memcpy(p->pack_name, path, path_len);
@@ -604,9 +593,9 @@ int git_packfile_check(struct git_pack_file **pack_out, const char *path)
 		p->pack_keep = 1;
 
 	strcpy(p->pack_name + path_len, ".pack");
-	if (p_stat(p->pack_name, &st) < GIT_SUCCESS || !S_ISREG(st.st_mode)) {
+	if (p_stat(p->pack_name, &st) < 0 || !S_ISREG(st.st_mode)) {
 		git__free(p);
-		return git__throw(GIT_ENOTFOUND, "Failed to check packfile. File not found");
+		return git_odb__error_notfound("packfile not found");
 	}
 
 	/* ok, it looks sane as far as we can check without
@@ -618,11 +607,12 @@ int git_packfile_check(struct git_pack_file **pack_out, const char *path)
 
 	/* see if we can parse the sha1 oid in the packfile name */
 	if (path_len < 40 ||
-		git_oid_fromstr(&p->sha1, path + path_len - GIT_OID_HEXSZ) < GIT_SUCCESS)
+		git_oid_fromstr(&p->sha1, path + path_len - GIT_OID_HEXSZ) < 0)
 		memset(&p->sha1, 0x0, GIT_OID_RAWSZ);
 
 	*pack_out = p;
-	return GIT_SUCCESS;
+
+	return 0;
 }
 
 /***********************************************************
@@ -631,7 +621,7 @@ int git_packfile_check(struct git_pack_file **pack_out, const char *path)
  *
  ***********************************************************/
 
-static off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n)
+static git_off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n)
 {
 	const unsigned char *index = p->index_map.data;
 	index += 4 * 256;
@@ -650,11 +640,11 @@ static off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n)
 }
 
 static int pack_entry_find_offset(
-		off_t *offset_out,
-		git_oid *found_oid,
-		struct git_pack_file *p,
-		const git_oid *short_oid,
-		unsigned int len)
+	git_off_t *offset_out,
+	git_oid *found_oid,
+	struct git_pack_file *p,
+	const git_oid *short_oid,
+	unsigned int len)
 {
 	const uint32_t *level1_ofs = p->index_map.data;
 	const unsigned char *index = p->index_map.data;
@@ -667,8 +657,8 @@ static int pack_entry_find_offset(
 	if (index == NULL) {
 		int error;
 
-		if ((error = pack_index_open(p)) < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to find offset for pack entry");
+		if ((error = pack_index_open(p)) < 0)
+			return error;
 
 		assert(p->index_map.data);
 
@@ -726,22 +716,22 @@ static int pack_entry_find_offset(
 		}
 	}
 
-	if (!found) {
-		return git__throw(GIT_ENOTFOUND, "Failed to find offset for pack entry. Entry not found");
-	} else if (found > 1) {
-		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to find offset for pack entry. Ambiguous sha1 prefix within pack");
-	} else {
-		*offset_out = nth_packed_object_offset(p, pos);
-		git_oid_fromraw(found_oid, current);
+	if (!found)
+		return git_odb__error_notfound("failed to find offset for pack entry");
+	if (found > 1)
+		return git_odb__error_ambiguous("found multiple offsets for pack entry");
+	*offset_out = nth_packed_object_offset(p, pos);
+	git_oid_fromraw(found_oid, current);
 
 #ifdef INDEX_DEBUG_LOOKUP
+	{
 		unsigned char hex_sha1[GIT_OID_HEXSZ + 1];
 		git_oid_fmt(hex_sha1, found_oid);
 		hex_sha1[GIT_OID_HEXSZ] = '\0';
 		printf("found lo=%d %s\n", lo, hex_sha1);
-#endif
-		return GIT_SUCCESS;
 	}
+#endif
+	return 0;
 }
 
 int git_pack_entry_find(
@@ -750,7 +740,7 @@ int git_pack_entry_find(
 		const git_oid *short_oid,
 		unsigned int len)
 {
-	off_t offset;
+	git_off_t offset;
 	git_oid found_oid;
 	int error;
 
@@ -760,22 +750,22 @@ int git_pack_entry_find(
 		unsigned i;
 		for (i = 0; i < p->num_bad_objects; i++)
 			if (git_oid_cmp(short_oid, &p->bad_object_sha1[i]) == 0)
-				return git__throw(GIT_ERROR, "Failed to find pack entry. Bad object found");
+				return packfile_error("bad object found in packfile");
 	}
 
 	error = pack_entry_find_offset(&offset, &found_oid, p, short_oid, len);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to find pack entry. Couldn't find offset");
+	if (error < 0)
+		return error;
 
 	/* we found a unique entry in the index;
 	 * make sure the packfile backing the index
 	 * still exists on disk */
-	if (p->mwf.fd == -1 && packfile_open(p) < GIT_SUCCESS)
-		return git__throw(GIT_EOSERR, "Failed to find pack entry. Packfile doesn't exist on disk");
+	if (p->mwf.fd == -1 && (error = packfile_open(p)) < 0)
+		return error;
 
 	e->offset = offset;
 	e->p = p;
 
 	git_oid_cpy(&e->sha1, &found_oid);
-	return GIT_SUCCESS;
+	return 0;
 }
diff --git a/src/pack.h b/src/pack.h
index 5902978..7cf41c1 100644
--- a/src/pack.h
+++ b/src/pack.h
@@ -70,7 +70,7 @@ struct git_pack_file {
 };
 
 struct git_pack_entry {
-	off_t offset;
+	git_off_t offset;
 	git_oid sha1;
 	struct git_pack_file *p;
 };
@@ -80,13 +80,13 @@ int git_packfile_unpack_header(
 		git_otype *type_p,
 		git_mwindow_file *mwf,
 		git_mwindow **w_curs,
-		off_t *curpos);
+		git_off_t *curpos);
 
-int git_packfile_unpack(git_rawobj *obj, struct git_pack_file *p, off_t *obj_offset);
+int git_packfile_unpack(git_rawobj *obj, struct git_pack_file *p, git_off_t *obj_offset);
 
-off_t get_delta_base(struct git_pack_file *p, git_mwindow **w_curs,
-		off_t *curpos, git_otype type,
-		off_t delta_obj_offset);
+git_off_t get_delta_base(struct git_pack_file *p, git_mwindow **w_curs,
+		git_off_t *curpos, git_otype type,
+		git_off_t delta_obj_offset);
 
 void packfile_free(struct git_pack_file *p);
 int git_packfile_check(struct git_pack_file **pack_out, const char *path);
diff --git a/src/path.c b/src/path.c
index 1ff257a..0f45d71 100644
--- a/src/path.c
+++ b/src/path.c
@@ -49,16 +49,14 @@ int git_path_basename_r(git_buf *buffer, const char *path)
 	while (startp > path && *(startp - 1) != '/')
 		startp--;
 
-	len = endp - startp +1;
+	/* Cast is safe because max path < max int */
+	len = (int)(endp - startp + 1);
 
 Exit:
 	result = len;
 
-	if (buffer != NULL) {
-		if (git_buf_set(buffer, startp, len) < GIT_SUCCESS)
-			return git__rethrow(GIT_ENOMEM,
-				"Could not get basename of '%s'", path);
-	}
+	if (buffer != NULL && git_buf_set(buffer, startp, len) < 0)
+		return -1;
 
 	return result;
 }
@@ -99,7 +97,8 @@ int git_path_dirname_r(git_buf *buffer, const char *path)
 		endp--;
 	} while (endp > path && *endp == '/');
 
-	len = endp - path +1;
+	/* Cast is safe because max path < max int */
+	len = (int)(endp - path + 1);
 
 #ifdef GIT_WIN32
 	/* Mimic unix behavior where '/.git' returns '/': 'C:/.git' will return
@@ -114,11 +113,8 @@ int git_path_dirname_r(git_buf *buffer, const char *path)
 Exit:
 	result = len;
 
-	if (buffer != NULL) {
-		if (git_buf_set(buffer, path, len) < GIT_SUCCESS)
-			return git__rethrow(GIT_ENOMEM,
-				"Could not get dirname of '%s'", path);
-	}
+	if (buffer != NULL && git_buf_set(buffer, path, len) < 0)
+		return -1;
 
 	return result;
 }
@@ -152,7 +148,7 @@ char *git_path_basename(const char *path)
 const char *git_path_topdir(const char *path)
 {
 	size_t len;
-	int i;
+	ssize_t i;
 
 	assert(path);
 	len = strlen(path);
@@ -160,7 +156,7 @@ const char *git_path_topdir(const char *path)
 	if (!len || path[len - 1] != '/')
 		return NULL;
 
-	for (i = len - 2; i >= 0; --i)
+	for (i = (ssize_t)len - 2; i >= 0; --i)
 		if (path[i] == '/')
 			break;
 
@@ -199,7 +195,8 @@ int git_path_prettify(git_buf *path_out, const char *path, const char *base)
 	}
 
 	if (p_realpath(path, buf) == NULL) {
-		giterr_set(GITERR_OS, "Failed to resolve path '%s': %s", path, strerror(errno));
+		giterr_set(GITERR_OS, "Failed to resolve path '%s': %s",
+			path, strerror(errno));
 		return (errno == ENOENT) ? GIT_ENOTFOUND : -1;
 	}
 
@@ -211,10 +208,8 @@ int git_path_prettify(git_buf *path_out, const char *path, const char *base)
 
 int git_path_prettify_dir(git_buf *path_out, const char *path, const char *base)
 {
-	if (git_path_prettify(path_out, path, base) < 0)
-		return -1;
-
-	return git_path_to_dir(path_out);
+	int error = git_path_prettify(path_out, path, base);
+	return (error < 0) ? error : git_path_to_dir(path_out);
 }
 
 int git_path_to_dir(git_buf *path)
@@ -224,10 +219,7 @@ int git_path_to_dir(git_buf *path)
 		path->ptr[path->size - 1] != '/')
 		git_buf_putc(path, '/');
 
-	if (git_buf_oom(path))
-		return -1;
-
-	return 0;
+	return git_buf_oom(path) ? -1 : 0;
 }
 
 void git_path_string_to_dir(char* path, size_t size)
@@ -242,10 +234,10 @@ void git_path_string_to_dir(char* path, size_t size)
 
 int git__percent_decode(git_buf *decoded_out, const char *input)
 {
-	int len, hi, lo, i, error = GIT_SUCCESS;
+	int len, hi, lo, i;
 	assert(decoded_out && input);
 
-	len = strlen(input);
+	len = (int)strlen(input);
 	git_buf_clear(decoded_out);
 
 	for(i = 0; i < len; i++)
@@ -268,39 +260,40 @@ int git__percent_decode(git_buf *decoded_out, const char *input)
 		i += 2;
 
 append:
-		error = git_buf_putc(decoded_out, c);
-		if (error < GIT_SUCCESS)
-			return git__rethrow(error, "Failed to percent decode '%s'.", input);
+		if (git_buf_putc(decoded_out, c) < 0)
+			return -1;
 	}
 
-	return error;
+	return 0;
+}
+
+static int error_invalid_local_file_uri(const char *uri)
+{
+	giterr_set(GITERR_CONFIG, "'%s' is not a valid local file URI", uri);
+	return -1;
 }
 
 int git_path_fromurl(git_buf *local_path_out, const char *file_url)
 {
-	int error = GIT_SUCCESS, offset = 0, len;
+	int offset = 0, len;
 
 	assert(local_path_out && file_url);
 
 	if (git__prefixcmp(file_url, "file://") != 0)
-		return git__throw(GIT_EINVALIDPATH,
-			"Parsing of '%s' failed. A file Uri is expected (ie. with 'file://' scheme).",
-			file_url);
+		return error_invalid_local_file_uri(file_url);
 
 	offset += 7;
-	len = strlen(file_url);
+	len = (int)strlen(file_url);
 
 	if (offset < len && file_url[offset] == '/')
 		offset++;
 	else if (offset < len && git__prefixcmp(file_url + offset, "localhost/") == 0)
 		offset += 10;
 	else
-		return git__throw(GIT_EINVALIDPATH,
-			"Parsing of '%s' failed. A local file Uri is expected.", file_url);
+		return error_invalid_local_file_uri(file_url);
 
 	if (offset >= len || file_url[offset] == '/')
-		return git__throw(GIT_EINVALIDPATH, 
-			"Parsing of '%s' failed. Invalid file Uri format.", file_url);
+		return error_invalid_local_file_uri(file_url);
 
 #ifndef _MSC_VER
 	offset--;	/* A *nix absolute path starts with a forward slash */
@@ -308,11 +301,7 @@ int git_path_fromurl(git_buf *local_path_out, const char *file_url)
 
 	git_buf_clear(local_path_out);
 
-	error = git__percent_decode(local_path_out, file_url + offset);
-	if (error < GIT_SUCCESS)
-		return git__rethrow(error, "Parsing of '%s' failed.", file_url);
-
-	return error;
+	return git__percent_decode(local_path_out, file_url + offset);
 }
 
 int git_path_walk_up(
@@ -321,7 +310,7 @@ int git_path_walk_up(
 	int (*cb)(void *data, git_buf *),
 	void *data)
 {
-	int error = GIT_SUCCESS;
+	int error = 0;
 	git_buf iter;
 	ssize_t stop = 0, scan;
 	char oldc = '\0';
@@ -341,7 +330,7 @@ int git_path_walk_up(
 	iter.asize = path->asize;
 
 	while (scan >= stop) {
-		if ((error = cb(data, &iter)) < GIT_SUCCESS)
+		if ((error = cb(data, &iter)) < 0)
 			break;
 		iter.ptr[scan] = oldc;
 		scan = git_buf_rfind_next(&iter, '/');
@@ -394,6 +383,18 @@ bool git_path_isfile(const char *path)
 	return S_ISREG(st.st_mode) != 0;
 }
 
+int git_path_lstat(const char *path, struct stat *st)
+{
+	int err = 0;
+
+	if (p_lstat(path, st) < 0) {
+		err = (errno == ENOENT) ? GIT_ENOTFOUND : -1;
+		giterr_set(GITERR_OS, "Failed to stat file '%s'", path);
+	}
+
+	return err;
+}
+
 static bool _check_dir_contents(
 	git_buf *dir,
 	const char *sub,
@@ -434,25 +435,24 @@ bool git_path_contains_file(git_buf *base, const char *file)
 
 int git_path_find_dir(git_buf *dir, const char *path, const char *base)
 {
-	int error = GIT_SUCCESS;
+	int error;
 
 	if (base != NULL && git_path_root(path) < 0)
 		error = git_buf_joinpath(dir, base, path);
 	else
 		error = git_buf_sets(dir, path);
 
-	if (error == GIT_SUCCESS) {
+	if (!error) {
 		char buf[GIT_PATH_MAX];
 		if (p_realpath(dir->ptr, buf) != NULL)
 			error = git_buf_sets(dir, buf);
 	}
 
 	/* call dirname if this is not a directory */
-	if (error == GIT_SUCCESS && git_path_isdir(dir->ptr) == false)
-		if (git_path_dirname_r(dir, dir->ptr) < GIT_SUCCESS)
-			error = GIT_ENOMEM;
+	if (!error && git_path_isdir(dir->ptr) == false)
+		error = git_path_dirname_r(dir, dir->ptr);
 
-	if (error == GIT_SUCCESS)
+	if (!error)
 		error = git_path_to_dir(dir);
 
 	return error;
@@ -497,9 +497,9 @@ int git_path_direach(
 		return -1;
 
 	wd_len = path->size;
-	dir = opendir(path->ptr);
-	if (!dir) {
-		giterr_set(GITERR_OS, "Failed to 'opendir' %s", path->ptr);
+
+	if ((dir = opendir(path->ptr)) == NULL) {
+		giterr_set(GITERR_OS, "Failed to open directory '%s'", path->ptr);
 		return -1;
 	}
 
@@ -541,9 +541,10 @@ int git_path_dirload(
 	path_len = strlen(path);
 	assert(path_len > 0 && path_len >= prefix_len);
 
-	if ((dir = opendir(path)) == NULL)
-		return git__throw(GIT_EOSERR, "Failed to process `%s` tree structure."
-			" An error occured while opening the directory", path);
+	if ((dir = opendir(path)) == NULL) {
+		giterr_set(GITERR_OS, "Failed to open directory '%s'", path);
+		return -1;
+	}
 
 	path += prefix_len;
 	path_len -= prefix_len;
@@ -560,8 +561,7 @@ int git_path_dirload(
 
 		entry_path = git__malloc(
 			path_len + need_slash + entry_len + 1 + alloc_extra);
-		if (entry_path == NULL)
-			return GIT_ENOMEM;
+		GITERR_CHECK_ALLOC(entry_path);
 
 		if (path_len)
 			memcpy(entry_path, path, path_len);
@@ -570,19 +570,16 @@ int git_path_dirload(
 		memcpy(&entry_path[path_len + need_slash], de->d_name, entry_len);
 		entry_path[path_len + need_slash + entry_len] = '\0';
 
-		if ((error = git_vector_insert(contents, entry_path)) < GIT_SUCCESS) {
-			git__free(entry_path);
-			return error;
-		}
+		if (git_vector_insert(contents, entry_path) < 0)
+			return -1;
 	}
 
 	closedir(dir);
 
-	if (error != GIT_SUCCESS)
-		return git__throw(
-			GIT_EOSERR, "Failed to process directory entry in `%s`", path);
+	if (error != 0)
+		giterr_set(GITERR_OS, "Failed to process directory entry in '%s'", path);
 
-	return GIT_SUCCESS;
+	return error;
 }
 
 int git_path_with_stat_cmp(const void *a, const void *b)
@@ -601,11 +598,12 @@ int git_path_dirload_with_stat(
 	git_path_with_stat *ps;
 	git_buf full = GIT_BUF_INIT;
 
-	if ((error = git_buf_set(&full, path, prefix_len)) != GIT_SUCCESS)
-		return error;
+	if (git_buf_set(&full, path, prefix_len) < 0)
+		return -1;
 
-	if ((error = git_path_dirload(path, prefix_len,
-		sizeof(git_path_with_stat) + 1, contents)) != GIT_SUCCESS) {
+	error = git_path_dirload(
+		path, prefix_len, sizeof(git_path_with_stat) + 1, contents);
+	if (error < 0) {
 		git_buf_free(&full);
 		return error;
 	}
@@ -616,8 +614,10 @@ int git_path_dirload_with_stat(
 		memmove(ps->path, ps, path_len + 1);
 		ps->path_len = path_len;
 
-		git_buf_joinpath(&full, full.ptr, ps->path);
-		p_lstat(full.ptr, &ps->st);
+		if ((error = git_buf_joinpath(&full, full.ptr, ps->path)) < 0 ||
+			(error = git_path_lstat(full.ptr, &ps->st)) < 0)
+			break;
+
 		git_buf_truncate(&full, prefix_len);
 
 		if (S_ISDIR(ps->st.st_mode)) {
diff --git a/src/path.h b/src/path.h
index e885d87..3cf7394 100644
--- a/src/path.h
+++ b/src/path.h
@@ -130,6 +130,11 @@ extern bool git_path_isdir(const char *path);
 extern bool git_path_isfile(const char *path);
 
 /**
+ * Stat a file and/or link and set error if needed.
+ */
+extern int git_path_lstat(const char *path, struct stat *st);
+
+/**
  * Check if the parent directory contains the item.
  *
  * @param dir Directory to check.
diff --git a/src/posix.c b/src/posix.c
index 9d96d30..9778809 100644
--- a/src/posix.c
+++ b/src/posix.c
@@ -34,9 +34,9 @@ int p_getcwd(char *buffer_out, size_t size)
 		return -1;
 
 	git_path_mkposix(buffer_out);
-	git_path_string_to_dir(buffer_out, size);	//Ensure the path ends with a trailing slash
+	git_path_string_to_dir(buffer_out, size); /* append trailing slash */
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int p_rename(const char *from, const char *to)
diff --git a/src/refs.c b/src/refs.c
index e90cf5d..b4c4b1e 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -842,7 +842,7 @@ static int reference_path_available(
 
 	if (!data.available) {
 		giterr_set(GITERR_REFERENCE,
-			"The path to reference '%s' collides with an existing one");
+			"The path to reference '%s' collides with an existing one", ref);
 		return -1;
 	}
 
@@ -902,7 +902,7 @@ static int reference_can_write(
 		 * the rename; the existing one would be overwritten */
 		if (exists) {
 			giterr_set(GITERR_REFERENCE,
-				"A reference with that name (%s) already exists");
+				"A reference with that name (%s) already exists", refname);
 			return GIT_EEXISTS;
 		}
 	}
diff --git a/src/repository.c b/src/repository.c
index 7d7b3c4..99eee52 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -377,17 +377,15 @@ void git_repository_set_index(git_repository *repo, git_index *index)
 
 static int retrieve_device(dev_t *device_out, const char *path)
 {
+	int error;
 	struct stat path_info;
 
 	assert(device_out);
 
-	if (p_lstat(path, &path_info)) {
-		giterr_set(GITERR_OS, "Failed to retrieve file information: %s", strerror(errno));
-		return -1;
-	}
+	if ((error = git_path_lstat(path, &path_info)) == 0)
+		*device_out = path_info.st_dev;
 
-	*device_out = path_info.st_dev;
-	return 0;
+	return error;
 }
 
 /*
diff --git a/src/unix/map.c b/src/unix/map.c
index 67a73e4..772f4e2 100644
--- a/src/unix/map.c
+++ b/src/unix/map.c
@@ -17,12 +17,7 @@ int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offs
 	int mprot = 0;
 	int mflag = 0;
 
-	assert((out != NULL) && (len > 0));
-
-	if ((out == NULL) || (len == 0)) {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. No map or zero length");
-	}
+	GIT_MMAP_VALIDATE(out, len, prot, flags);
 
 	out->data = NULL;
 	out->len = 0;
@@ -31,39 +26,28 @@ int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offs
 		mprot = PROT_WRITE;
 	else if (prot & GIT_PROT_READ)
 		mprot = PROT_READ;
-	else {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. Invalid protection parameters");
-	}
 
 	if ((flags & GIT_MAP_TYPE) == GIT_MAP_SHARED)
 		mflag = MAP_SHARED;
 	else if ((flags & GIT_MAP_TYPE) == GIT_MAP_PRIVATE)
 		mflag = MAP_PRIVATE;
 
-	if (flags & GIT_MAP_FIXED) {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. FIXED not set");
+	out->data = mmap(NULL, len, mprot, mflag, fd, offset);
+	if (!out->data || out->data == MAP_FAILED) {
+		giterr_set(GITERR_OS, "Failed to mmap. Could not write data");
+		return -1;
 	}
 
-	out->data = mmap(NULL, len, mprot, mflag, fd, offset);
-	if (!out->data || out->data == MAP_FAILED)
-		return git__throw(GIT_EOSERR, "Failed to mmap. Could not write data");
 	out->len = len;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int p_munmap(git_map *map)
 {
 	assert(map != NULL);
-
-	if (!map)
-		return git__throw(GIT_ERROR, "Failed to munmap. Map does not exist");
-
 	munmap(map->data, map->len);
-
-	return GIT_SUCCESS;
+	return 0;
 }
 
 #endif
diff --git a/src/win32/dir.c b/src/win32/dir.c
index 035e2b6..bc3d40f 100644
--- a/src/win32/dir.c
+++ b/src/win32/dir.c
@@ -27,8 +27,8 @@ static int init_filter(char *filter, size_t n, const char *dir)
 git__DIR *git__opendir(const char *dir)
 {
 	char filter[4096];
-	wchar_t* filter_w;
-	git__DIR *new;
+	wchar_t* filter_w = NULL;
+	git__DIR *new = NULL;
 
 	if (!dir || !init_filter(filter, sizeof(filter), dir))
 		return NULL;
@@ -37,25 +37,29 @@ git__DIR *git__opendir(const char *dir)
 	if (!new)
 		return NULL;
 
-	new->dir = git__malloc(strlen(dir)+1);
-	if (!new->dir) {
-		git__free(new);
-		return NULL;
-	}
-	strcpy(new->dir, dir);
+	new->dir = git__strdup(dir);
+	if (!new->dir)
+		goto fail;
 
 	filter_w = gitwin_to_utf16(filter);
+	if (!filter_w)
+		goto fail;
+
 	new->h = FindFirstFileW(filter_w, &new->f);
 	git__free(filter_w);
 
 	if (new->h == INVALID_HANDLE_VALUE) {
-		git__free(new->dir);
-		git__free(new);
-		return NULL;
+		giterr_set(GITERR_OS, "Could not open directory '%s'", dir);
+		goto fail;
 	}
-	new->first = 1;
 
+	new->first = 1;
 	return new;
+
+fail:
+	git__free(new->dir);
+	git__free(new);
+	return NULL;
 }
 
 int git__readdir_ext(
@@ -67,22 +71,32 @@ int git__readdir_ext(
 	if (!d || !entry || !result || d->h == INVALID_HANDLE_VALUE)
 		return -1;
 
+	*result = NULL;
+
 	if (d->first)
 		d->first = 0;
 	else if (!FindNextFileW(d->h, &d->f)) {
-		*result = NULL;
-		return 0;
+		if (GetLastError() == ERROR_NO_MORE_FILES)
+			return 0;
+		giterr_set(GITERR_OS, "Could not read from directory '%s'", d->dir);
+		return -1;
 	}
 
 	if (wcslen(d->f.cFileName) >= sizeof(entry->d_name))
 		return -1;
 
 	entry->d_ino = 0;
-	WideCharToMultiByte(
+
+	if (WideCharToMultiByte(
 		gitwin_get_codepage(), 0, d->f.cFileName, -1,
-		entry->d_name, GIT_PATH_MAX, NULL, NULL);
+		entry->d_name, GIT_PATH_MAX, NULL, NULL) == 0)
+	{
+		giterr_set(GITERR_OS, "Could not convert filename to UTF-8");
+		return -1;
+	}
 
 	*result = entry;
+
 	if (is_dir != NULL)
 		*is_dir = ((d->f.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0);
 
@@ -102,32 +116,40 @@ void git__rewinddir(git__DIR *d)
 	char filter[4096];
 	wchar_t* filter_w;
 
-	if (d) {
-		if (d->h != INVALID_HANDLE_VALUE)
-			FindClose(d->h);
+	if (!d)
+		return;
+
+	if (d->h != INVALID_HANDLE_VALUE) {
+		FindClose(d->h);
 		d->h = INVALID_HANDLE_VALUE;
 		d->first = 0;
+	}
 
-		if (init_filter(filter, sizeof(filter), d->dir)) {
-			filter_w = gitwin_to_utf16(filter);
-			d->h = FindFirstFileW(filter_w, &d->f);
-			git__free(filter_w);
+	if (!init_filter(filter, sizeof(filter), d->dir) ||
+		(filter_w = gitwin_to_utf16(filter)) == NULL)
+		return;
 
-			if (d->h != INVALID_HANDLE_VALUE)
-				d->first = 1;
-		}
-	}
+	d->h = FindFirstFileW(filter_w, &d->f);
+	git__free(filter_w);
+
+	if (d->h == INVALID_HANDLE_VALUE)
+		giterr_set(GITERR_OS, "Could not open directory '%s'", d->dir);
+	else
+		d->first = 1;
 }
 
 int git__closedir(git__DIR *d)
 {
-	if (d) {
-		if (d->h != INVALID_HANDLE_VALUE)
-			FindClose(d->h);
-		if (d->dir)
-			git__free(d->dir);
-		git__free(d);
+	if (!d)
+		return 0;
+
+	if (d->h != INVALID_HANDLE_VALUE) {
+		FindClose(d->h);
+		d->h = INVALID_HANDLE_VALUE;
 	}
+	git__free(d->dir);
+	d->dir = NULL;
+	git__free(d);
 	return 0;
 }
 
diff --git a/src/win32/map.c b/src/win32/map.c
index 60adf0f..f730120 100644
--- a/src/win32/map.c
+++ b/src/win32/map.c
@@ -33,12 +33,7 @@ int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offs
 	git_off_t page_start;
 	git_off_t page_offset;
 
-	assert((out != NULL) && (len > 0));
-
-	if ((out == NULL) || (len == 0)) {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. No map or zero length");
-	}
+	GIT_MMAP_VALIDATE(out, len, prot, flags);
 
 	out->data = NULL;
 	out->len = 0;
@@ -46,86 +41,75 @@ int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offs
 
 	if (fh == INVALID_HANDLE_VALUE) {
 		errno = EBADF;
-		return git__throw(GIT_ERROR, "Failed to mmap. Invalid handle value");
+		giterr_set(GITERR_OS, "Failed to mmap. Invalid handle value");
+		return -1;
 	}
 
 	if (prot & GIT_PROT_WRITE)
 		fmap_prot |= PAGE_READWRITE;
 	else if (prot & GIT_PROT_READ)
 		fmap_prot |= PAGE_READONLY;
-	else {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. Invalid protection parameters");
-	}
 
 	if (prot & GIT_PROT_WRITE)
 		view_prot |= FILE_MAP_WRITE;
 	if (prot & GIT_PROT_READ)
 		view_prot |= FILE_MAP_READ;
 
-	if (flags & GIT_MAP_FIXED) {
-		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. FIXED not set");
-	}
-
 	page_start = (offset / page_size) * page_size;
 	page_offset = offset - page_start;
 
 	if (page_offset != 0) { /* offset must be multiple of page size */
 		errno = EINVAL;
-		return git__throw(GIT_ERROR, "Failed to mmap. Offset must be multiple of page size");
+		giterr_set(GITERR_OS, "Failed to mmap. Offset must be multiple of page size");
+		return -1;
 	}
 
 	out->fmh = CreateFileMapping(fh, NULL, fmap_prot, 0, 0, NULL);
 	if (!out->fmh || out->fmh == INVALID_HANDLE_VALUE) {
-		/* errno = ? */
+		giterr_set(GITERR_OS, "Failed to mmap. Invalid handle value");
 		out->fmh = NULL;
-		return git__throw(GIT_ERROR, "Failed to mmap. Invalid handle value");
+		return -1;
 	}
 
 	assert(sizeof(git_off_t) == 8);
+
 	off_low = (DWORD)(page_start);
 	off_hi = (DWORD)(page_start >> 32);
 	out->data = MapViewOfFile(out->fmh, view_prot, off_hi, off_low, len);
 	if (!out->data) {
-		/* errno = ? */
+		giterr_set(GITERR_OS, "Failed to mmap. No data written");
 		CloseHandle(out->fmh);
 		out->fmh = NULL;
-		return git__throw(GIT_ERROR, "Failed to mmap. No data written");
+		return -1;
 	}
 	out->len = len;
 
-	return GIT_SUCCESS;
+	return 0;
 }
 
 int p_munmap(git_map *map)
 {
-	assert(map != NULL);
+	int error = 0;
 
-	if (!map)
-		return git__throw(GIT_ERROR, "Failed to munmap. Map does not exist");
+	assert(map != NULL);
 
 	if (map->data) {
 		if (!UnmapViewOfFile(map->data)) {
-			/* errno = ? */
-			CloseHandle(map->fmh);
-			map->data = NULL;
-			map->fmh = NULL;
-			return git__throw(GIT_ERROR, "Failed to munmap. Could not unmap view of file");
+			giterr_set(GITERR_OS, "Failed to munmap. Could not unmap view of file");
+			error = -1;
 		}
 		map->data = NULL;
 	}
 
 	if (map->fmh) {
 		if (!CloseHandle(map->fmh)) {
-			/* errno = ? */
-			map->fmh = NULL;
-			return git__throw(GIT_ERROR, "Failed to munmap. Could not close handle");
+			giterr_set(GITERR_OS, "Failed to munmap. Could not close handle");
+			error = -1;
 		}
 		map->fmh = NULL;
 	}
 
-	return GIT_SUCCESS;
+	return error;
 }
 
 
diff --git a/src/win32/posix_w32.c b/src/win32/posix_w32.c
index 2d7c2e3..c6b36a8 100644
--- a/src/win32/posix_w32.c
+++ b/src/win32/posix_w32.c
@@ -1,4 +1,4 @@
-/ < 0)
+/*
  * Copyright (C) 2009-2012 the libgit2 contributors
  *
  * This file is part of libgit2, distributed under the GNU GPL v2 with
@@ -17,10 +17,11 @@ int p_unlink(const char *path)
 	int ret = 0;
 	wchar_t* buf;
 
-	buf = gitwin_to_utf16(path);
-	_wchmod(buf, 0666);
-	ret = _wunlink(buf);
-	git__free(buf);
+	if ((buf = gitwin_to_utf16(path)) != NULL) {
+		_wchmod(buf, 0666);
+		ret = _wunlink(buf);
+		git__free(buf);
+	}
 
 	return ret;
 }
@@ -60,6 +61,8 @@ static int do_lstat(const char *file_name, struct stat *buf)
 {
 	WIN32_FILE_ATTRIBUTE_DATA fdata;
 	wchar_t* fbuf = gitwin_to_utf16(file_name);
+	if (!fbuf)
+		return -1;
 
 	if (GetFileAttributesExW(fbuf, GetFileExInfoStandard, &fdata)) {
 		int fMode = S_IREAD;
@@ -87,54 +90,43 @@ static int do_lstat(const char *file_name, struct stat *buf)
 		buf->st_ctime = filetime_to_time_t(&(fdata.ftCreationTime));
 
 		git__free(fbuf);
-		return GIT_SUCCESS;
+		return 0;
 	}
 
 	git__free(fbuf);
-
-	switch (GetLastError()) {
-		case ERROR_ACCESS_DENIED:
-		case ERROR_SHARING_VIOLATION:
-		case ERROR_LOCK_VIOLATION:
-		case ERROR_SHARING_BUFFER_EXCEEDED:
-			return GIT_EOSERR;
-
-		case ERROR_BUFFER_OVERFLOW:
-		case ERROR_NOT_ENOUGH_MEMORY:
-			return GIT_ENOMEM;
-
-		default:
-			return GIT_EINVALIDPATH;
-	}
+	return -1;
 }
 
 int p_lstat(const char *file_name, struct stat *buf)
 {
-	int namelen, error;
-	char alt_name[GIT_PATH_MAX];
+	int error;
+	size_t namelen;
+	char *alt_name;
 
-	if ((error = do_lstat(file_name, buf)) == GIT_SUCCESS)
-		return GIT_SUCCESS;
+	if (do_lstat(file_name, buf) == 0)
+		return 0;
 
 	/* if file_name ended in a '/', Windows returned ENOENT;
 	 * try again without trailing slashes
 	 */
-	if (error != GIT_EINVALIDPATH)
-		return git__throw(GIT_EOSERR, "Failed to lstat file");
-
 	namelen = strlen(file_name);
 	if (namelen && file_name[namelen-1] != '/')
-		return git__throw(GIT_EOSERR, "Failed to lstat file");
+		return -1;
 
 	while (namelen && file_name[namelen-1] == '/')
 		--namelen;
 
-	if (!namelen || namelen >= GIT_PATH_MAX)
-		return git__throw(GIT_ENOMEM, "Failed to lstat file");
+	if (!namelen)
+		return -1;
+
+	alt_name = git__strndup(file_name, namelen);
+	if (!alt_name)
+		return -1;
+
+	error = do_lstat(alt_name, buf);
 
-	memcpy(alt_name, file_name, namelen);
-	alt_name[namelen] = 0;
-	return do_lstat(alt_name, buf);
+	git__free(alt_name);
+	return error;
 }
 
 int p_readlink(const char *link, char *target, size_t target_len)
@@ -145,6 +137,9 @@ int p_readlink(const char *link, char *target, size_t target_len)
 	DWORD dwRet;
 	wchar_t* link_w;
 	wchar_t* target_w;
+	int error = 0;
+
+	assert(link && target && target_len > 0);
 
 	/*
 	 * Try to load the pointer to pGetFinalPath dynamically, because
@@ -156,12 +151,15 @@ int p_readlink(const char *link, char *target, size_t target_len)
 		if (library != NULL)
 			pGetFinalPath = (fpath_func)GetProcAddress(library, "GetFinalPathNameByHandleW");
 
-		if (pGetFinalPath == NULL)
-			return git__throw(GIT_EOSERR,
+		if (pGetFinalPath == NULL) {
+			giterr_set(GITERR_OS,
 				"'GetFinalPathNameByHandleW' is not available in this platform");
+			return -1;
+		}
 	}
 
 	link_w = gitwin_to_utf16(link);
+	GITERR_CHECK_ALLOC(link_w);
 
 	hFile = CreateFileW(link_w,			// file to open
 			GENERIC_READ,			// open for reading
@@ -173,50 +171,49 @@ int p_readlink(const char *link, char *target, size_t target_len)
 
 	git__free(link_w);
 
-	if (hFile == INVALID_HANDLE_VALUE)
-		return GIT_EOSERR;
-
-	if (target_len <= 0) {
-		return GIT_EINVALIDARGS;
+	if (hFile == INVALID_HANDLE_VALUE) {
+		giterr_set(GITERR_OS, "Cannot open '%s' for reading", link);
+		return -1;
 	}
 
 	target_w = (wchar_t*)git__malloc(target_len * sizeof(wchar_t));
+	GITERR_CHECK_ALLOC(target_w);
 
 	dwRet = pGetFinalPath(hFile, target_w, target_len, 0x0);
-	if (dwRet >= target_len) {
-		git__free(target_w);
-		CloseHandle(hFile);
-		return GIT_ENOMEM;
-	}
-
-	if (!WideCharToMultiByte(CP_UTF8, 0, target_w, -1, target, target_len * sizeof(char), NULL, NULL)) {
-		git__free(target_w);
-		return GIT_EOSERR;
-	}
+	if (dwRet == 0 ||
+		dwRet >= target_len ||
+		!WideCharToMultiByte(CP_UTF8, 0, target_w, -1, target,
+			target_len * sizeof(char), NULL, NULL))
+		error = -1;
 
 	git__free(target_w);
 	CloseHandle(hFile);
 
-	if (dwRet > 4) {
-		/* Skip first 4 characters if they are "\\?\" */
-		if (target[0] == '\\' && target[1] == '\\' && target[2] == '?' && target[3] == '\\') {
-			char tmp[GIT_PATH_MAX];
-			unsigned int offset = 4;
-			dwRet -= 4;
-
-			/* \??\UNC\ */
-			if (dwRet > 7 && target[4] == 'U' && target[5] == 'N' && target[6] == 'C') {
-				offset += 2;
-				dwRet -= 2;
-				target[offset] = '\\';
-			}
-
-			memcpy(tmp, target + offset, dwRet);
-			memcpy(target, tmp, dwRet);
+	if (error)
+		return error;
+
+	/* Skip first 4 characters if they are "\\?\" */
+	if (dwRet > 4 &&
+		target[0] == '\\' && target[1] == '\\' &&
+		target[2] == '?' && target[3] == '\\')
+	{
+		unsigned int offset = 4;
+		dwRet -= 4;
+
+		/* \??\UNC\ */
+		if (dwRet > 7 &&
+			target[4] == 'U' && target[5] == 'N' && target[6] == 'C')
+		{
+			offset += 2;
+			dwRet -= 2;
+			target[offset] = '\\';
 		}
+
+		memmove(target, target + offset, dwRet);
 	}
 
 	target[dwRet] = '\0';
+
 	return dwRet;
 }
 
@@ -224,8 +221,9 @@ int p_open(const char *path, int flags)
 {
 	int fd;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 	fd = _wopen(buf, flags | _O_BINARY);
-
 	git__free(buf);
 	return fd;
 }
@@ -234,8 +232,9 @@ int p_creat(const char *path, mode_t mode)
 {
 	int fd;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 	fd = _wopen(buf, _O_WRONLY | _O_CREAT | _O_TRUNC | _O_BINARY, mode);
-
 	git__free(buf);
 	return fd;
 }
@@ -243,15 +242,15 @@ int p_creat(const char *path, mode_t mode)
 int p_getcwd(char *buffer_out, size_t size)
 {
 	wchar_t* buf = (wchar_t*)git__malloc(sizeof(wchar_t) * (int)size);
+	int ret;
+
 	_wgetcwd(buf, (int)size);
 
-	if (!WideCharToMultiByte(CP_UTF8, 0, buf, -1, buffer_out, size, NULL, NULL)) {
-		git__free(buf);
-		return GIT_EOSERR;
-	}
+	ret = WideCharToMultiByte(
+		CP_UTF8, 0, buf, -1, buffer_out, size, NULL, NULL);
 
 	git__free(buf);
-	return GIT_SUCCESS;
+	return !ret ? -1 : 0;
 }
 
 int p_stat(const char* path, struct stat* buf)
@@ -262,8 +261,10 @@ int p_stat(const char* path, struct stat* buf)
 int p_chdir(const char* path)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wchdir(buf);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wchdir(buf);
 	git__free(buf);
 	return ret;
 }
@@ -271,8 +272,10 @@ int p_chdir(const char* path)
 int p_chmod(const char* path, mode_t mode)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wchmod(buf, mode);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wchmod(buf, mode);
 	git__free(buf);
 	return ret;
 }
@@ -280,8 +283,10 @@ int p_chmod(const char* path, mode_t mode)
 int p_rmdir(const char* path)
 {
 	wchar_t* buf = gitwin_to_utf16(path);
-	int ret = _wrmdir(buf);
-
+	int ret;
+	if (!buf)
+		return -1;
+	ret = _wrmdir(buf);
 	git__free(buf);
 	return ret;
 }
@@ -290,11 +295,13 @@ int p_hide_directory__w32(const char *path)
 {
 	int res;
 	wchar_t* buf = gitwin_to_utf16(path);
+	if (!buf)
+		return -1;
 
 	res = SetFileAttributesW(buf, FILE_ATTRIBUTE_HIDDEN);
 	git__free(buf);
-	
-	return (res != 0) ?  GIT_SUCCESS : GIT_ERROR; /* MSDN states a "non zero" value indicates a success */
+
+	return (res != 0) ? 0 : -1; /* MSDN states a "non zero" value indicates a success */
 }
 
 char *p_realpath(const char *orig_path, char *buffer)
@@ -303,6 +310,9 @@ char *p_realpath(const char *orig_path, char *buffer)
 	wchar_t* orig_path_w = gitwin_to_utf16(orig_path);
 	wchar_t* buffer_w = (wchar_t*)git__malloc(GIT_PATH_MAX * sizeof(wchar_t));
 
+	if (!orig_path_w || !buffer_w)
+		return NULL;
+
 	ret = GetFullPathNameW(orig_path_w, GIT_PATH_MAX, buffer_w, NULL);
 	git__free(orig_path_w);
 
@@ -339,7 +349,7 @@ int p_vsnprintf(char *buffer, size_t count, const char *format, va_list argptr)
 	int len;
 
 	if (count == 0 || (len = _vsnprintf(buffer, count, format, argptr)) < 0)
-		return p_vscprintf(format, argptr);
+		return _vscprintf(format, argptr);
 
 	return len;
 #else /* MinGW */
@@ -365,10 +375,10 @@ int p_mkstemp(char *tmp_path)
 {
 #if defined(_MSC_VER)
 	if (_mktemp_s(tmp_path, strlen(tmp_path) + 1) != 0)
-		return GIT_EOSERR;
+		return -1;
 #else
 	if (_mktemp(tmp_path) == NULL)
-		return GIT_EOSERR;
+		return -1;
 #endif
 
 	return p_creat(tmp_path, 0744);
@@ -377,15 +387,17 @@ int p_mkstemp(char *tmp_path)
 int p_setenv(const char* name, const char* value, int overwrite)
 {
 	if (overwrite != 1)
-		return EINVAL;
+		return -1;
 
-	return (SetEnvironmentVariableA(name, value) == 0 ? GIT_EOSERR : GIT_SUCCESS);
+	return (SetEnvironmentVariableA(name, value) == 0 ? -1 : 0);
 }
 
 int p_access(const char* path, mode_t mode)
 {
 	wchar_t *buf = gitwin_to_utf16(path);
 	int ret;
+	if (!buf)
+		return -1;
 
 	ret = _waccess(buf, mode);
 	git__free(buf);
@@ -393,13 +405,16 @@ int p_access(const char* path, mode_t mode)
 	return ret;
 }
 
-extern int p_rename(const char *from, const char *to)
+int p_rename(const char *from, const char *to)
 {
 	wchar_t *wfrom = gitwin_to_utf16(from);
 	wchar_t *wto = gitwin_to_utf16(to);
 	int ret;
 
-	ret = MoveFileExW(wfrom, wto, MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED) ? GIT_SUCCESS : GIT_EOSERR;
+	if (!wfrom || !wto)
+		return -1;
+
+	ret = MoveFileExW(wfrom, wto, MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED) ? 0 : -1;
 
 	git__free(wfrom);
 	git__free(wto);
diff --git a/src/win32/pthread.c b/src/win32/pthread.c
index 3db5368..3a186c8 100644
--- a/src/win32/pthread.c
+++ b/src/win32/pthread.c
@@ -7,13 +7,16 @@
 
 #include "pthread.h"
 
-int pthread_create(pthread_t *GIT_RESTRICT thread,
-					const pthread_attr_t *GIT_RESTRICT attr,
-					void *(*start_routine)(void*), void *GIT_RESTRICT arg)
+int pthread_create(
+	pthread_t *GIT_RESTRICT thread,
+	const pthread_attr_t *GIT_RESTRICT attr,
+	void *(*start_routine)(void*),
+	void *GIT_RESTRICT arg)
 {
 	GIT_UNUSED(attr);
-	*thread = (pthread_t) CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)start_routine, arg, 0, NULL);
-	return *thread ? GIT_SUCCESS : git__throw(GIT_EOSERR, "Failed to create pthread");
+	*thread = (pthread_t) CreateThread(
+		NULL, 0, (LPTHREAD_START_ROUTINE)start_routine, arg, 0, NULL);
+	return *thread ? 0 : -1;
 }
 
 int pthread_join(pthread_t thread, void **value_ptr)
diff --git a/src/win32/utf-conv.c b/src/win32/utf-conv.c
index 3c8be81..f00f5be 100644
--- a/src/win32/utf-conv.c
+++ b/src/win32/utf-conv.c
@@ -33,14 +33,14 @@ wchar_t* gitwin_to_utf16(const char* str)
 	wchar_t* ret;
 	int cb;
 
-	if (!str) {
+	if (!str)
 		return NULL;
-	}
 
 	cb = strlen(str) * sizeof(wchar_t);
 	if (cb == 0) {
 		ret = (wchar_t*)git__malloc(sizeof(wchar_t));
-		ret[0] = 0;
+		if (ret)
+			ret[0] = 0;
 		return ret;
 	}
 
@@ -48,8 +48,11 @@ wchar_t* gitwin_to_utf16(const char* str)
 	cb += sizeof(wchar_t);
 
 	ret = (wchar_t*)git__malloc(cb);
+	if (!ret)
+		return NULL;
 
 	if (MultiByteToWideChar(_active_codepage, 0, str, -1, ret, cb) == 0) {
+		giterr_set(GITERR_OS, "Could not convert string to UTF-16");
 		git__free(ret);
 		ret = NULL;
 	}
@@ -59,7 +62,10 @@ wchar_t* gitwin_to_utf16(const char* str)
 
 int gitwin_append_utf16(wchar_t *buffer, const char *str, size_t len)
 {
-	return MultiByteToWideChar(_active_codepage, 0, str, -1, buffer, len);
+	int result = MultiByteToWideChar(_active_codepage, 0, str, -1, buffer, len);
+	if (result == 0)
+		giterr_set(GITERR_OS, "Could not convert string to UTF-16");
+	return result;
 }
 
 char* gitwin_from_utf16(const wchar_t* str)
@@ -74,7 +80,8 @@ char* gitwin_from_utf16(const wchar_t* str)
 	cb = wcslen(str) * sizeof(char);
 	if (cb == 0) {
 		ret = (char*)git__malloc(sizeof(char));
-		ret[0] = 0;
+		if (ret)
+			ret[0] = 0;
 		return ret;
 	}
 
@@ -82,8 +89,11 @@ char* gitwin_from_utf16(const wchar_t* str)
 	cb += sizeof(char);
 
 	ret = (char*)git__malloc(cb);
+	if (!ret)
+		return NULL;
 
 	if (WideCharToMultiByte(_active_codepage, 0, str, -1, ret, cb, NULL, NULL) == 0) {
+		giterr_set(GITERR_OS, "Could not convert string to UTF-8");
 		git__free(ret);
 		ret = NULL;
 	}
diff --git a/tests-clar/attr/attr_expect.h b/tests-clar/attr/attr_expect.h
index bea5624..b064eac 100644
--- a/tests-clar/attr/attr_expect.h
+++ b/tests-clar/attr/attr_expect.h
@@ -15,7 +15,7 @@ struct attr_expected {
 	const char *expected_str;
 };
 
-static inline void attr_check_expected(
+GIT_INLINE(void) attr_check_expected(
 	enum attr_expect_t expected,
 	const char *expected_str,
 	const char *value)
diff --git a/tests-clar/core/errors.c b/tests-clar/core/errors.c
new file mode 100644
index 0000000..52b2652
--- /dev/null
+++ b/tests-clar/core/errors.c
@@ -0,0 +1,74 @@
+#include "clar_libgit2.h"
+#include "common.h"
+#include "util.h"
+#include "posix.h"
+
+#ifdef git__throw
+void test_core_errors__old_school(void)
+{
+	git_clearerror();
+	cl_assert(git_lasterror() == NULL);
+
+	cl_assert(git_strerror(GIT_ENOTFOUND) != NULL);
+
+	git__throw(GIT_ENOTFOUND, "My Message");
+	cl_assert(git_lasterror() != NULL);
+	cl_assert(git__prefixcmp(git_lasterror(), "My Message") == 0);
+	git_clearerror();
+}
+#endif
+
+#ifdef GITERR_CHECK_ALLOC
+void test_core_errors__new_school(void)
+{
+	char *str_in_error;
+
+	git_error_clear();
+	cl_assert(git_error_last() == NULL);
+
+	giterr_set_oom(); /* internal fn */
+
+	cl_assert(git_error_last() != NULL);
+	cl_assert(git_error_last()->klass == GITERR_NOMEMORY);
+	str_in_error = strstr(git_error_last()->message, "memory");
+	cl_assert(str_in_error != NULL);
+
+	git_error_clear();
+
+	giterr_set(GITERR_REPOSITORY, "This is a test"); /* internal fn */
+
+	cl_assert(git_error_last() != NULL);
+	str_in_error = strstr(git_error_last()->message, "This is a test");
+	cl_assert(str_in_error != NULL);
+
+	git_error_clear();
+
+	{
+		struct stat st;
+		assert(p_lstat("this_file_does_not_exist", &st) < 0);
+	}
+	giterr_set(GITERR_OS, "stat failed"); /* internal fn */
+
+	cl_assert(git_error_last() != NULL);
+	str_in_error = strstr(git_error_last()->message, "stat failed");
+	cl_assert(str_in_error != NULL);
+	cl_assert(git__prefixcmp(str_in_error, "stat failed: ") == 0);
+	cl_assert(strlen(str_in_error) > strlen("stat failed: "));
+
+#ifdef GIT_WIN32
+	git_error_clear();
+
+	/* The MSDN docs use this to generate a sample error */
+	cl_assert(GetProcessId(NULL) == 0);
+	giterr_set(GITERR_OS, "GetProcessId failed"); /* internal fn */
+
+	cl_assert(git_error_last() != NULL);
+	str_in_error = strstr(git_error_last()->message, "GetProcessId failed");
+	cl_assert(str_in_error != NULL);
+	cl_assert(git__prefixcmp(str_in_error, "GetProcessId failed: ") == 0);
+	cl_assert(strlen(str_in_error) > strlen("GetProcessId failed: "));
+#endif
+
+	git_error_clear();
+}
+#endif