thodg/libgit2

diff --git a/include/git2/odb.h b/include/git2/odb.h
index b3e9a57..3e93a93 100644
--- a/include/git2/odb.h
+++ b/include/git2/odb.h
@@ -219,16 +219,9 @@ GIT_EXTERN(int) git_odb_write(git_oid *out, git_odb *odb, const void *data, size
  * The type and final length of the object must be specified
  * when opening the stream.
  *
- * The returned stream will be of type `GIT_STREAM_WRONLY` and
- * will have the following methods:
- *
- *		- stream->write: write `n` bytes into the stream
- *		- stream->finalize_write: close the stream and store the object in
- *			the odb
- *		- stream->free: free the stream
- *
- * The streaming write won't be effective until `stream->finalize_write`
- * is called and returns without an error
+ * The returned stream will be of type `GIT_STREAM_WRONLY`, and it
+ * won't be effective until `git_odb_stream_finalize_write` is called
+ * and returns without an error
  *
  * The stream must always be free'd or will leak memory.
  *
@@ -243,6 +236,42 @@ GIT_EXTERN(int) git_odb_write(git_oid *out, git_odb *odb, const void *data, size
 GIT_EXTERN(int) git_odb_open_wstream(git_odb_stream **out, git_odb *db, size_t size, git_otype type);
 
 /**
+ * Write to an odb stream
+ *
+ * @param stream the stream
+ * @param buffer the data to write
+ * @param len the buffer's length
+ * @return 0 if the write succeeded; error code otherwise
+ */
+GIT_EXTERN(int) git_odb_stream_write(git_odb_stream *stream, const char *buffer, size_t len);
+
+/**
+ * Finish writing to an odb stream
+ *
+ * The object will take its final name and will be available to the
+ * odb.
+ *
+ * @param out pointer to store the resulting object's id
+ * @param stream the stream
+ * @return 0 on success; an error code otherwise
+ */
+GIT_EXTERN(int) git_odb_stream_finalize_write(git_oid *out, git_odb_stream *stream);
+
+/**
+ * Read from an odb stream
+ *
+ * Most backends don't implement streaming reads
+ */
+GIT_EXTERN(int) git_odb_stream_read(git_odb_stream *stream, char *buffer, size_t len);
+
+/**
+ * Free an odb stream
+ *
+ * @param stream the stream to free
+ */
+GIT_EXTERN(void) git_odb_stream_free(git_odb_stream *stream);
+
+/**
  * Open a stream to read an object from the ODB
  *
  * Note that most backends do *not* support streaming reads
diff --git a/include/git2/odb_backend.h b/include/git2/odb_backend.h
index af1e3e5..dca4995 100644
--- a/include/git2/odb_backend.h
+++ b/include/git2/odb_backend.h
@@ -65,14 +65,41 @@ typedef enum {
 	GIT_STREAM_RW = (GIT_STREAM_RDONLY | GIT_STREAM_WRONLY),
 } git_odb_stream_t;
 
-/** A stream to read/write from a backend */
+typedef struct git_hash_ctx git_hash_ctx;
+
+/**
+ * A stream to read/write from a backend.
+ *
+ * This represents a stream of data being written to or read from a
+ * backend. When writing, the frontend functions take care of
+ * calculating the object's id and all `finalize_write` needs to do is
+ * store the object with the id it is passed.
+ */
 struct git_odb_stream {
 	git_odb_backend *backend;
 	unsigned int mode;
+	git_hash_ctx *hash_ctx;
 
+	/**
+	 * Write at most `len` bytes into `buffer` and advance the
+	 * stream.
+	 */
 	int (*read)(git_odb_stream *stream, char *buffer, size_t len);
+
+	/**
+	 * Write `len` bytes from `buffer` into the stream.
+	 */
 	int (*write)(git_odb_stream *stream, const char *buffer, size_t len);
-	int (*finalize_write)(git_oid *oid_p, git_odb_stream *stream);
+
+	/**
+	 * Store the contents of the stream as an object with the id
+	 * specified in `oid`.
+	 */
+	int (*finalize_write)(git_odb_stream *stream, const git_oid *oid);
+
+	/**
+	 * Free the stream's memory.
+	 */
 	void (*free)(git_odb_stream *stream);
 };
 
diff --git a/include/git2/sys/odb_backend.h b/include/git2/sys/odb_backend.h
index 3cd2734..31ffe1c 100644
--- a/include/git2/sys/odb_backend.h
+++ b/include/git2/sys/odb_backend.h
@@ -48,12 +48,12 @@ struct git_odb_backend {
 	int (* read_header)(
 		size_t *, git_otype *, git_odb_backend *, const git_oid *);
 
-	/* The writer may assume that the object
-	 * has already been hashed and is passed
-	 * in the first parameter.
+	/**
+	 * Write an object into the backend. The id of the object has
+	 * already been calculated and is passed in.
 	 */
 	int (* write)(
-		git_oid *, git_odb_backend *, const void *, size_t, git_otype);
+		git_odb_backend *, const git_oid *, const void *, size_t, git_otype);
 
 	int (* writestream)(
 		git_odb_stream **, git_odb_backend *, size_t, git_otype);
diff --git a/src/blob.c b/src/blob.c
index 5bb51f7..6a289f4 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -60,10 +60,10 @@ int git_blob_create_frombuffer(git_oid *oid, git_repository *repo, const void *b
 		(error = git_odb_open_wstream(&stream, odb, len, GIT_OBJ_BLOB)) < 0)
 		return error;
 
-	if ((error = stream->write(stream, buffer, len)) == 0)
-		error = stream->finalize_write(oid, stream);
+	if ((error = git_odb_stream_write(stream, buffer, len)) == 0)
+		error = git_odb_stream_finalize_write(oid, stream);
 
-	stream->free(stream);
+	git_odb_stream_free(stream);
 	return error;
 }
 
@@ -80,12 +80,12 @@ static int write_file_stream(
 		return error;
 
 	if ((fd = git_futils_open_ro(path)) < 0) {
-		stream->free(stream);
+		git_odb_stream_free(stream);
 		return -1;
 	}
 
 	while (!error && (read_len = p_read(fd, buffer, sizeof(buffer))) > 0) {
-		error = stream->write(stream, buffer, read_len);
+		error = git_odb_stream_write(stream, buffer, read_len);
 		written += read_len;
 	}
 
@@ -97,9 +97,9 @@ static int write_file_stream(
 	}
 
 	if (!error)
-		error = stream->finalize_write(oid, stream);
+		error = git_odb_stream_finalize_write(oid, stream);
 
-	stream->free(stream);
+	git_odb_stream_free(stream);
 	return error;
 }
 
diff --git a/src/odb.c b/src/odb.c
index 6969cf7..21b46bf 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -291,10 +291,10 @@ typedef struct {
 	git_otype type;
 } fake_wstream;
 
-static int fake_wstream__fwrite(git_oid *oid, git_odb_stream *_stream)
+static int fake_wstream__fwrite(git_odb_stream *_stream, const git_oid *oid)
 {
 	fake_wstream *stream = (fake_wstream *)_stream;
-	return _stream->backend->write(oid, _stream->backend, stream->buffer, stream->size, stream->type);
+	return _stream->backend->write(_stream->backend, oid, stream->buffer, stream->size, stream->type);
 }
 
 static int fake_wstream__write(git_odb_stream *_stream, const char *data, size_t len)
@@ -851,7 +851,7 @@ int git_odb_write(
 			continue;
 
 		if (b->write != NULL)
-			error = b->write(oid, b, data, len, type);
+			error = b->write(b, oid, data, len, type);
 	}
 
 	if (!error || error == GIT_PASSTHROUGH)
@@ -865,17 +865,27 @@ int git_odb_write(
 		return error;
 
 	stream->write(stream, data, len);
-	error = stream->finalize_write(oid, stream);
-	stream->free(stream);
+	error = stream->finalize_write(stream, oid);
+	git_odb_stream_free(stream);
 
 	return error;
 }
 
+static void hash_header(git_hash_ctx *ctx, size_t size, git_otype type)
+{
+	char header[64];
+	int hdrlen;
+
+	hdrlen = git_odb__format_object_header(header, sizeof(header), size, type);
+	git_hash_update(ctx, header, hdrlen);
+}
+
 int git_odb_open_wstream(
 	git_odb_stream **stream, git_odb *db, size_t size, git_otype type)
 {
 	size_t i, writes = 0;
 	int error = GIT_ERROR;
+	git_hash_ctx *ctx;
 
 	assert(stream && db);
 
@@ -901,9 +911,40 @@ int git_odb_open_wstream(
 	if (error < 0 && !writes)
 		error = git_odb__error_unsupported_in_backend("write object");
 
+	ctx = git__malloc(sizeof(git_hash_ctx));
+	GITERR_CHECK_ALLOC(ctx);
+
+
+	git_hash_ctx_init(ctx);
+	hash_header(ctx, size, type);
+	(*stream)->hash_ctx = ctx;
+
 	return error;
 }
 
+int git_odb_stream_write(git_odb_stream *stream, const char *buffer, size_t len)
+{
+	git_hash_update(stream->hash_ctx, buffer, len);
+	return stream->write(stream, buffer, len);
+}
+
+int git_odb_stream_finalize_write(git_oid *out, git_odb_stream *stream)
+{
+	git_hash_final(out, stream->hash_ctx);
+	return stream->finalize_write(stream, out);
+}
+
+int git_odb_stream_read(git_odb_stream *stream, char *buffer, size_t len)
+{
+	return stream->read(stream, buffer, len);
+}
+
+void git_odb_stream_free(git_odb_stream *stream)
+{
+	git__free(stream->hash_ctx);
+	stream->free(stream);
+}
+
 int git_odb_open_rstream(git_odb_stream **stream, git_odb *db, const git_oid *oid)
 {
 	size_t i, reads = 0;
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 90e2587..abf46a1 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -771,15 +771,14 @@ static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb 
 	return state.cb_error ? state.cb_error : error;
 }
 
-static int loose_backend__stream_fwrite(git_oid *oid, git_odb_stream *_stream)
+static int loose_backend__stream_fwrite(git_odb_stream *_stream, const git_oid *oid)
 {
 	loose_writestream *stream = (loose_writestream *)_stream;
 	loose_backend *backend = (loose_backend *)_stream->backend;
 	git_buf final_path = GIT_BUF_INIT;
 	int error = 0;
 
-	if (git_filebuf_hash(oid, &stream->fbuf) < 0 ||
-		object_file_name(&final_path, backend, oid) < 0 ||
+	if (object_file_name(&final_path, backend, oid) < 0 ||
 		object_mkdir(&final_path, backend) < 0)
 		error = -1;
 	/*
@@ -812,17 +811,6 @@ static void loose_backend__stream_free(git_odb_stream *_stream)
 	git__free(stream);
 }
 
-static int format_object_header(char *hdr, size_t n, size_t obj_len, git_otype obj_type)
-{
-	const char *type_str = git_object_type2string(obj_type);
-	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! */
-
-	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;
@@ -836,7 +824,7 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 	backend = (loose_backend *)_backend;
 	*stream_out = NULL;
 
-	hdrlen = format_object_header(hdr, sizeof(hdr), length, type);
+	hdrlen = git_odb__format_object_header(hdr, sizeof(hdr), length, type);
 
 	stream = git__calloc(1, sizeof(loose_writestream));
 	GITERR_CHECK_ALLOC(stream);
@@ -850,7 +838,6 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 
 	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)
@@ -865,7 +852,7 @@ static int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_
 	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)
+static int loose_backend__write(git_odb_backend *_backend, const git_oid *oid, const void *data, size_t len, git_otype type)
 {
 	int error = 0, header_len;
 	git_buf final_path = GIT_BUF_INIT;
@@ -876,7 +863,7 @@ 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);
+	header_len = git_odb__format_object_header(header, sizeof(header), len, type);
 
 	if (git_buf_joinpath(&final_path, backend->objects_dir, "tmp_object") < 0 ||
 		git_filebuf_open(&fbuf, final_path.ptr,
diff --git a/src/tag.c b/src/tag.c
index 71f4c1e..31a3c8b 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -366,10 +366,10 @@ int git_tag_create_frombuffer(git_oid *oid, git_repository *repo, const char *bu
 	if (git_odb_open_wstream(&stream, odb, strlen(buffer), GIT_OBJ_TAG) < 0)
 		return -1;
 
-	stream->write(stream, buffer, strlen(buffer));
+	git_odb_stream_write(stream, buffer, strlen(buffer));
 
-	error = stream->finalize_write(oid, stream);
-	stream->free(stream);
+	error = git_odb_stream_finalize_write(oid, stream);
+	git_odb_stream_free(stream);
 
 	if (error < 0) {
 		git_buf_free(&ref_name);
diff --git a/src/transports/local.c b/src/transports/local.c
index a9da814..8a75de7 100644
--- a/src/transports/local.c
+++ b/src/transports/local.c
@@ -287,9 +287,9 @@ static int local_push_copy_object(
 		odb_obj_size, odb_obj_type)) < 0)
 		goto on_error;
 
-	if (odb_stream->write(odb_stream, (char *)git_odb_object_data(odb_obj),
+	if (git_odb_stream_write(odb_stream, (char *)git_odb_object_data(odb_obj),
 		odb_obj_size) < 0 ||
-		odb_stream->finalize_write(&remote_odb_obj_oid, odb_stream) < 0) {
+		git_odb_stream_finalize_write(&remote_odb_obj_oid, odb_stream) < 0) {
 		error = -1;
 	} else if (git_oid__cmp(&obj->id, &remote_odb_obj_oid) != 0) {
 		giterr_set(GITERR_ODB, "Error when writing object to remote odb "
@@ -298,7 +298,7 @@ static int local_push_copy_object(
 		error = -1;
 	}
 
-	odb_stream->free(odb_stream);
+	git_odb_stream_free(odb_stream);
 
 on_error:
 	git_odb_object_free(odb_obj);
diff --git a/tests-clar/object/raw/write.c b/tests-clar/object/raw/write.c
index 9709c03..273f08f 100644
--- a/tests-clar/object/raw/write.c
+++ b/tests-clar/object/raw/write.c
@@ -31,9 +31,9 @@ static void streaming_write(git_oid *oid, git_odb *odb, git_rawobj *raw)
    int error;
 
    cl_git_pass(git_odb_open_wstream(&stream, odb, raw->len, raw->type));
-   stream->write(stream, raw->data, raw->len);
-   error = stream->finalize_write(oid, stream);
-   stream->free(stream);
+   git_odb_stream_write(stream, raw->data, raw->len);
+   error = git_odb_stream_finalize_write(oid, stream);
+   git_odb_stream_free(stream);
    cl_git_pass(error);
 }