thodg/libgit2

diff --git a/include/git2/sys/filter.h b/include/git2/sys/filter.h
index aa89c7b..94ad3ae 100644
--- a/include/git2/sys/filter.h
+++ b/include/git2/sys/filter.h
@@ -125,23 +125,54 @@ GIT_EXTERN(git_filter_mode_t) git_filter_source_mode(const git_filter_source *sr
  * The filter lifecycle:
  * - initialize - first use of filter
  * - shutdown   - filter removed/unregistered from system
- * - check      - considering for file
- * - apply      - applied to file
+ * - check      - considering filter for file
+ * - apply      - apply filter to file contents
  * - cleanup    - done with file
  */
 
 /**
  * Initialize callback on filter
+ *
+ * Specified as `filter.initialize`, this is an optional callback invoked
+ * before a filter is first used.  It will be called once at most.
+ *
+ * If non-NULL, the filter's `initialize` callback will be invoked right
+ * before the first use of the filter, so you can defer expensive
+ * initialization operations (in case libgit2 is being used in a way that
+ * doesn't need the filter).
  */
 typedef int (*git_filter_init_fn)(git_filter *self);
 
 /**
  * Shutdown callback on filter
+ *
+ * Specified as `filter.shutdown`, this is an optional callback invoked
+ * when the filter is unregistered or when libgit2 is shutting down.  It
+ * will be called once at most and should release resources as needed.
+ *
+ * Typically this function will free the `git_filter` object itself.
  */
 typedef void (*git_filter_shutdown_fn)(git_filter *self);
 
 /**
  * Callback to decide if a given source needs this filter
+ *
+ * Specified as `filter.check`, this is an optional callback that checks
+ * if filtering is needed for a given source.
+ *
+ * It should return 0 if the filter should be applied (i.e. success),
+ * GIT_PASSTHROUGH if the filter should not be applied, or an error code
+ * to fail out of the filter processing pipeline and return to the caller.
+ *
+ * The `attr_values` will be set to the values of any attributes given in
+ * the filter definition.  See `git_filter` below for more detail.
+ *
+ * The `payload` will be a pointer to a reference payload for the filter.
+ * This will start as NULL, but `check` can assign to this pointer for
+ * later use by the `apply` callback.  Note that the value should be heap
+ * allocated (not stack), so that it doesn't go away before the `apply`
+ * callback can use it.  If a filter allocates and assigns a value to the
+ * `payload`, it will need a `cleanup` callback to free the payload.
  */
 typedef int (*git_filter_check_fn)(
 	git_filter  *self,
@@ -151,6 +182,15 @@ typedef int (*git_filter_check_fn)(
 
 /**
  * Callback to actually perform the data filtering
+ *
+ * Specified as `filter.apply`, this is the callback that actually filters
+ * data.  If it successfully writes the output, it should return 0.  Like
+ * `check`, it can return GIT_PASSTHROUGH to indicate that the filter
+ * doesn't want to run.  Other error codes will stop filter processing and
+ * return to the caller.
+ *
+ * The `payload` value will refer to any payload that was set by the
+ * `check` callback.  It may be read from or written to as needed.
  */
 typedef int (*git_filter_apply_fn)(
 	git_filter    *self,
@@ -161,18 +201,22 @@ typedef int (*git_filter_apply_fn)(
 
 /**
  * Callback to clean up after filtering has been applied
+ *
+ * Specified as `filter.cleanup`, this is an optional callback invoked
+ * after the filter has been applied.  If the `check` or `apply` callbacks
+ * allocated a `payload` to keep per-source filter state, use this
+ * callback to free that payload and release resources as required.
  */
 typedef void (*git_filter_cleanup_fn)(
 	git_filter *self,
 	void       *payload);
 
 /**
- * Filter structure used to register a new filter.
+ * Filter structure used to register custom filters.
  *
- * To associate extra data with a filter, simply allocate extra data
- * and put the `git_filter` struct at the start of your data buffer,
- * then cast the `self` pointer to your larger structure when your
- * callback is invoked.
+ * To associate extra data with a filter, allocate extra data and put the
+ * `git_filter` struct at the start of your data buffer, then cast the
+ * `self` pointer to your larger structure when your callback is invoked.
  *
  * `version` should be set to GIT_FILTER_VERSION
  *
@@ -182,28 +226,8 @@ typedef void (*git_filter_cleanup_fn)(
  * a value (i.e. "name=value"), the attribute must match that value for
  * the filter to be applied.
  *
- * `initialize` is an optional callback invoked before a filter is first
- * used.  It will be called once at most.
- *
- * `shutdown` is an optional callback invoked when the filter is
- * unregistered or when libgit2 is shutting down.  It will be called once
- * at most and should free any memory as needed.
- *
- * `check` is an optional callback that checks if filtering is needed for
- * a given source.  It should return 0 if the filter should be applied
- * (i.e. success), GIT_ENOTFOUND if the filter should not be applied, or
- * an other error code to fail out of the filter processing pipeline and
- * return to the caller.
- *
- * `apply` is the callback that actually filters data.  If it successfully
- * writes the output, it should return 0.  Like `check`, it can return
- * GIT_ENOTFOUND to indicate that the filter doesn't actually want to run.
- * Other error codes will stop filter processing and return to the caller.
- *
- * `cleanup` is an optional callback that is made after the filter has
- * been applied.  Both the `check` and `apply` callbacks are able to
- * allocate a `payload` to keep per-source filter state, and this callback
- * is given that value and can clean up as needed.
+ * The `initialize`, `shutdown`, `check`, `apply`, and `cleanup` callbacks
+ * are all documented above with the respective function pointer typedefs.
  */
 struct git_filter {
 	unsigned int           version;
@@ -222,9 +246,8 @@ struct git_filter {
 /**
  * Register a filter under a given name with a given priority.
  *
- * If non-NULL, the filter's initialize callback will be invoked before
- * the first use of the filter, so you can defer expensive operations (in
- * case libgit2 is being used in a way that doesn't need the filter).
+ * As mentioned elsewhere, the initialize callback will not be invoked
+ * immediately.  It is deferred until the filter is used in some way.
  *
  * A filter's attribute checks and `check` and `apply` callbacks will be
  * issued in order of `priority` on smudge (to workdir), and in reverse
@@ -237,6 +260,14 @@ struct git_filter {
  * Currently the filter registry is not thread safe, so any registering or
  * deregistering of filters must be done outside of any possible usage of
  * the filters (i.e. during application setup or shutdown).
+ *
+ * @param name A name by which the filter can be referenced.  Attempting
+ * 			to register with an in-use name will return GIT_EEXISTS.
+ * @param filter The filter definition.  This pointer will be stored as is
+ * 			by libgit2 so it must be a durable allocation (either static
+ * 			or on the heap).
+ * @param priority The priority for filter application
+ * @return 0 on successful registry, error code <0 on failure
  */
 GIT_EXTERN(int) git_filter_register(
 	const char *name, git_filter *filter, int priority);
@@ -244,11 +275,15 @@ GIT_EXTERN(int) git_filter_register(
 /**
  * Remove the filter with the given name
  *
- * It is not allowed to remove the builtin libgit2 filters.
+ * Attempting to remove the builtin libgit2 filters is not permitted and
+ * will return an error.
  *
  * Currently the filter registry is not thread safe, so any registering or
  * deregistering of filters must be done outside of any possible usage of
  * the filters (i.e. during application setup or shutdown).
+ *
+ * @param name The name under which the filter was registered
+ * @return 0 on success, error code <0 on failure
  */
 GIT_EXTERN(int) git_filter_unregister(const char *name);
 
diff --git a/src/array.h b/src/array.h
index b82079b..d7272d7 100644
--- a/src/array.h
+++ b/src/array.h
@@ -59,7 +59,7 @@ GIT_INLINE(void *) git_array_grow(void *_a, size_t item_size)
 #define git_array_alloc(a) \
 	((a).size >= (a).asize) ? \
 	git_array_grow(&(a), sizeof(*(a).ptr)) : \
-	(a).ptr ? &(a).ptr[(a).size++] : NULL
+	((a).ptr ? &(a).ptr[(a).size++] : NULL)
 
 #define git_array_last(a) ((a).size ? &(a).ptr[(a).size - 1] : NULL)
 
diff --git a/src/crlf.c b/src/crlf.c
index 6b1fe46..b4eda26 100644
--- a/src/crlf.c
+++ b/src/crlf.c
@@ -143,7 +143,7 @@ static int crlf_apply_to_odb(
 		 * stuff?
 		 */
 		if (stats.cr != stats.crlf)
-			return GIT_ENOTFOUND;
+			return GIT_PASSTHROUGH;
 
 		if (ca->crlf_action == GIT_CRLF_GUESS) {
 			/*
@@ -151,11 +151,11 @@ static int crlf_apply_to_odb(
 			 * This is the new safer autocrlf handling.
 			 */
 			if (has_cr_in_index(src))
-				return GIT_ENOTFOUND;
+				return GIT_PASSTHROUGH;
 		}
 
 		if (!stats.cr)
-			return GIT_ENOTFOUND;
+			return GIT_PASSTHROUGH;
 	}
 
 	/* Actually drop the carriage returns */
@@ -211,7 +211,7 @@ static int crlf_apply_to_workdir(
 
 	/* Don't filter binary files */
 	if (git_buf_text_is_binary(from))
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	/* Determine proper line ending */
 	workdir_ending = line_ending(ca);
@@ -220,10 +220,10 @@ static int crlf_apply_to_workdir(
 
 	if (!strcmp("\n", workdir_ending)) {
 		if (ca->crlf_action == GIT_CRLF_GUESS && ca->auto_crlf)
-			return GIT_ENOTFOUND;
+			return GIT_PASSTHROUGH;
 
 		if (git_buf_find(from, '\r') < 0)
-			return GIT_ENOTFOUND;
+			return GIT_PASSTHROUGH;
 
 		if (git_buf_text_crlf_to_lf(to, from) < 0)
 			return -1;
@@ -267,7 +267,7 @@ static int crlf_check(
 	ca.crlf_action = crlf_input_action(&ca);
 
 	if (ca.crlf_action == GIT_CRLF_BINARY)
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	if (ca.crlf_action == GIT_CRLF_GUESS) {
 		error = git_repository__cvar(
@@ -276,7 +276,7 @@ static int crlf_check(
 			return error;
 
 		if (ca.auto_crlf == GIT_AUTO_CRLF_FALSE)
-			return GIT_ENOTFOUND;
+			return GIT_PASSTHROUGH;
 	}
 
 	*payload = git__malloc(sizeof(ca));
@@ -296,7 +296,7 @@ static int crlf_apply(
 	/* initialize payload in case `check` was bypassed */
 	if (!*payload) {
 		int error = crlf_check(self, payload, src, NULL);
-		if (error < 0 && error != GIT_ENOTFOUND)
+		if (error < 0 && error != GIT_PASSTHROUGH)
 			return error;
 	}
 
diff --git a/src/filter.c b/src/filter.c
index 3782098..503f185 100644
--- a/src/filter.c
+++ b/src/filter.c
@@ -235,7 +235,7 @@ int git_filter_register(
 	if (!filter_registry_find(NULL, name)) {
 		giterr_set(
 			GITERR_FILTER, "Attempt to reregister existing filter '%s'", name);
-		return -1;
+		return GIT_EEXISTS;
 	}
 
 	if (filter_def_scan_attrs(&attrs, &nattr, &nmatch, filter->attributes) < 0)
@@ -270,7 +270,7 @@ int git_filter_unregister(const char *name)
 	git_filter_def *fdef;
 
 	/* cannot unregister default filters */
-	if (!strcmp(GIT_FILTER_CRLF, name)) {
+	if (!strcmp(GIT_FILTER_CRLF, name) || !strcmp(GIT_FILTER_IDENT, name)) {
 		giterr_set(GITERR_FILTER, "Cannot unregister filter '%s'", name);
 		return -1;
 	}
@@ -476,7 +476,7 @@ int git_filter_list_load(
 
 		git__free((void *)values);
 
-		if (error == GIT_ENOTFOUND)
+		if (error == GIT_PASSTHROUGH)
 			error = 0;
 		else if (error < 0)
 			break;
@@ -609,11 +609,13 @@ int git_filter_list_apply_to_data(
 		error = fe->filter->apply(
 			fe->filter, &fe->payload, dbuffer[di], dbuffer[si], &fl->source);
 
-		if (error == GIT_ENOTFOUND)
+		if (error == GIT_PASSTHROUGH) {
+			/* PASSTHROUGH means filter decided not to process the buffer */
 			error = 0;
-		else if (!error)
+		} else if (!error) {
+			git_buf_shorten(dbuffer[di], 0); /* force NUL termination */
 			si = di; /* swap buffers */
-		else {
+		} else {
 			tgt->size = 0;
 			return error;
 		}
diff --git a/src/ident.c b/src/ident.c
index 23c407f..5163087 100644
--- a/src/ident.c
+++ b/src/ident.c
@@ -13,23 +13,25 @@
 static int ident_find_id(
 	const char **id_start, const char **id_end, const char *start, size_t len)
 {
-	const char *found;
+	const char *end = start + len, *found = NULL;
 
-	while (len > 0 && (found = memchr(start, '$', len)) != NULL) {
-		size_t remaining = len - (size_t)(found - start);
+	while (len > 3 && (found = memchr(start, '$', len)) != NULL) {
+		size_t remaining = (size_t)(end - found) - 1;
 		if (remaining < 3)
 			return GIT_ENOTFOUND;
-		if (found[1] == 'I' && found[2] == 'd')
-			break;
+
 		start = found + 1;
-		len = remaining - 1;
+		len   = remaining;
+
+		if (start[0] == 'I' && start[1] == 'd')
+			break;
 	}
 
-	if (!found || len < 3)
+	if (len < 3 || !found)
 		return GIT_ENOTFOUND;
 	*id_start = found;
 
-	if ((found = memchr(found + 3, '$', len - 3)) == NULL)
+	if ((found = memchr(start + 2, '$', len - 2)) == NULL)
 		return GIT_ENOTFOUND;
 
 	*id_end = found + 1;
@@ -46,12 +48,12 @@ static int ident_insert_id(
 	/* replace $Id$ with blob id */
 
 	if (!git_filter_source_id(src))
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	git_oid_tostr(oid, sizeof(oid), git_filter_source_id(src));
 
 	if (ident_find_id(&id_start, &id_end, from->ptr, from->size) < 0)
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	need_size = (size_t)(id_start - from->ptr) +
 		5 /* "$Id: " */ + GIT_OID_HEXSZ + 1 /* "$" */ +
@@ -76,7 +78,7 @@ static int ident_remove_id(
 	size_t need_size;
 
 	if (ident_find_id(&id_start, &id_end, from->ptr, from->size) < 0)
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	need_size = (size_t)(id_start - from->ptr) +
 		4 /* "$Id$" */ + (size_t)(from_end - id_end);
@@ -102,7 +104,7 @@ static int ident_apply(
 
 	/* Don't filter binary files */
 	if (git_buf_text_is_binary(from))
-		return GIT_ENOTFOUND;
+		return GIT_PASSTHROUGH;
 
 	if (git_filter_source_mode(src) == GIT_FILTER_SMUDGE)
 		return ident_insert_id(to, from, src);
diff --git a/src/win32/pthread.c b/src/win32/pthread.c
index 8c7ef28..db89274 100644
--- a/src/win32/pthread.c
+++ b/src/win32/pthread.c
@@ -6,6 +6,7 @@
  */
 
 #include "pthread.h"
+#include "../global.h"
 
 int pthread_create(
 	pthread_t *GIT_RESTRICT thread,
diff --git a/tests-clar/filter/custom.c b/tests-clar/filter/custom.c
index d6ad4b7..a81885c 100644
--- a/tests-clar/filter/custom.c
+++ b/tests-clar/filter/custom.c
@@ -6,9 +6,11 @@
 #include "git2/sys/filter.h"
 #include "git2/sys/repository.h"
 
-/* picked these to be >= GIT_FILTER_DRIVER_PRIORITY */
-#define BITFLIP_FILTER_PRIORITY 200
-#define REVERSE_FILTER_PRIORITY 250
+/* going TO_WORKDIR, filters are executed low to high
+ * going TO_ODB, filters are executed high to low
+ */
+#define BITFLIP_FILTER_PRIORITY -1
+#define REVERSE_FILTER_PRIORITY -2
 
 #define VERY_SECURE_ENCRYPTION(b) ((b) ^ 0xff)
 
@@ -149,13 +151,13 @@ static void reverse_filter_free(git_filter *f)
 	git__free(f);
 }
 
-static git_filter *create_reverse_filter(void)
+static git_filter *create_reverse_filter(const char *attrs)
 {
 	git_filter *filter = git__calloc(1, sizeof(git_filter));
 	cl_assert(filter);
 
 	filter->version = GIT_FILTER_VERSION;
-	filter->attributes = "+reverse";
+	filter->attributes = attrs;
 	filter->shutdown = reverse_filter_free;
 	filter->apply = reverse_filter_apply;
 
@@ -171,7 +173,14 @@ static void register_custom_filters(void)
 			"bitflip", create_bitflip_filter(), BITFLIP_FILTER_PRIORITY));
 
 		cl_git_pass(git_filter_register(
-			"reverse", create_reverse_filter(), REVERSE_FILTER_PRIORITY));
+			"reverse", create_reverse_filter("+reverse"),
+			REVERSE_FILTER_PRIORITY));
+
+		/* re-register reverse filter with standard filter=xyz priority */
+		cl_git_pass(git_filter_register(
+			"pre-reverse",
+			create_reverse_filter("+prereverse"),
+			GIT_FILTER_DRIVER_PRIORITY));
 
 		filters_registered = 1;
 	}
@@ -273,7 +282,7 @@ void test_filter_custom__order_dependency(void)
 
 	cl_git_mkfile(
 		"empty_standard_repo/.gitattributes",
-		"hero.*.rev-ident text ident reverse eol=lf\n");
+		"hero.*.rev-ident text ident prereverse eol=lf\n");
 
 	cl_git_mkfile(
 		"empty_standard_repo/hero.1.rev-ident",
@@ -315,3 +324,14 @@ void test_filter_custom__order_dependency(void)
 
 	git_buf_free(&buf);
 }
+
+void test_filter_custom__filter_registry_failure_cases(void)
+{
+	git_filter fake = { GIT_FILTER_VERSION, 0 };
+
+	cl_assert_equal_i(GIT_EEXISTS, git_filter_register("bitflip", &fake, 0));
+
+	cl_git_fail(git_filter_unregister(GIT_FILTER_CRLF));
+	cl_git_fail(git_filter_unregister(GIT_FILTER_IDENT));
+	cl_assert_equal_i(GIT_ENOTFOUND, git_filter_unregister("not-a-filter"));
+}