Internal changes on the backend system

The priority value for different backends has been removed from the
public `git_odb_backend` struct. We handle that internally. The priority
value is specified on the `git_odb_add_alternate`.

This is convenient because it allows us to poll a backend twice with
different priorities without having to instantiate it twice.

We also differentiate between main backends and alternates; alternates have
lower priority and cannot be written to.

These changes come with some unit tests to make sure that the backend
sorting is consistent.

The libgit2 version has been bumped to 0.4.0.

This commit changes the external API:

CHANGED:
	struct git_odb_backend
		No longer has a `priority` attribute; priority for the backend
		in managed internally by the library.

	git_odb_add_backend(git_odb *odb, git_odb_backend *backend, int priority)
		Now takes an additional priority parameter, the priority that
		will be given to the backend.

ADDED:
	git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority)
		Add a backend as an alternate. Alternate backends have always
		lower priority than main backends, and writing is disabled on
		them.

Signed-off-by: Vicent Marti <tanoku@gmail.com>

Signed-off-by: Vicent Marti <tanoku@gmail.com>

src/backends/sqlite.c

@@ -264,8 +264,6 @@ int git_odb_backend_sqlite(git_odb_backend **backend_out, const char *sqlite_db)
 	backend->parent.exists = &sqlite_backend__exists;
 	backend->parent.free = &sqlite_backend__free;
 
-	backend->parent.priority = 0; 
-
 	*backend_out = (git_odb_backend *)backend;
 	return GIT_SUCCESS;
 

src/git2.h

@@ -26,9 +26,9 @@
 #ifndef INCLUDE_git_git_h__
 #define INCLUDE_git_git_h__
 
-#define LIBGIT2_VERSION "0.3.0"
+#define LIBGIT2_VERSION "0.4.0"
 #define LIBGIT2_VER_MAJOR 0
-#define LIBGIT2_VER_MINOR 3
+#define LIBGIT2_VER_MINOR 4
 #define LIBGIT2_VER_REVISION 0
 
 #include "git2/common.h"

src/git2/odb.h

@@ -79,7 +79,24 @@ GIT_EXTERN(int) git_odb_open(git_odb **out, const char *objects_dir);
  * @paramm backend pointer to a git_odb_backend instance
  * @return 0 on sucess; error code otherwise
  */
-GIT_EXTERN(int) git_odb_add_backend(git_odb *odb, git_odb_backend *backend);
+GIT_EXTERN(int) git_odb_add_backend(git_odb *odb, git_odb_backend *backend, int priority);
+
+/**
+ * Add a custom backend to an existing Object DB; this
+ * backend will work as an alternate.
+ *
+ * Alternate backends are always checked for objects *after*
+ * all the main backends have been exhausted.
+ *
+ * Writing is disabled on alternate backends.
+ *
+ * Read <odb_backends.h> for more information.
+ *
+ * @param odb database to add the backend to
+ * @paramm backend pointer to a git_odb_backend instance
+ * @return 0 on sucess; error code otherwise
+ */
+GIT_EXTERN(int) git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority);
 
 /**
  * Close an open object database.

src/git2/odb_backend.h

@@ -42,8 +42,6 @@ GIT_BEGIN_DECL
 struct git_odb_backend {
 	git_odb *odb;
 
-	int priority;
-
 	int (* read)(
 			git_rawobj *,
 			struct git_odb_backend *,

src/odb.c

@@ -35,6 +35,17 @@
 
 #define GIT_ALTERNATES_FILE "info/alternates"
 
+/* TODO: is this correct? */
+#define GIT_LOOSE_PRIORITY 2
+#define GIT_PACKED_PRIORITY 1
+
+typedef struct
+{
+	git_odb_backend *backend;
+	int priority;
+	int is_alternate;
+} backend_internal;
+
 static int format_object_header(char *hdr, size_t n, git_rawobj *obj)
 {
 	const char *type_str = git_object_type2string(obj->type);
@@ -136,10 +147,13 @@ int git_odb__inflate_buffer(void *in, size_t inlen, void *out, size_t outlen)
 
 int backend_sort_cmp(const void *a, const void *b)
 {
-	const git_odb_backend *backend_a = *(const git_odb_backend **)(a);
-	const git_odb_backend *backend_b = *(const git_odb_backend **)(b);
+	const backend_internal *backend_a = *(const backend_internal **)(a);
+	const backend_internal *backend_b = *(const backend_internal **)(b);
+
+	if (backend_a->is_alternate == backend_b->is_alternate)
+		return (backend_b->priority - backend_a->priority);
 
-	return (backend_b->priority - backend_a->priority);
+	return backend_a->is_alternate ? 1 : -1;
 }
 
 int git_odb_new(git_odb **out)
@@ -157,23 +171,44 @@ int git_odb_new(git_odb **out)
 	return GIT_SUCCESS;
 }
 
-int git_odb_add_backend(git_odb *odb, git_odb_backend *backend)
+static int add_backend_internal(git_odb *odb, git_odb_backend *backend, int priority, int is_alternate)
 {
+	backend_internal *internal;
+
 	assert(odb && backend);
 
 	if (backend->odb != NULL && backend->odb != odb)
 		return GIT_EBUSY;
 
-	backend->odb = odb;
+	internal = git__malloc(sizeof(backend_internal));
+	if (internal == NULL)
+		return GIT_ENOMEM;
+
+	internal->backend = backend;
+	internal->priority = priority;
+	internal->is_alternate = is_alternate;
 
-	if (git_vector_insert(&odb->backends, backend) < 0)
+	if (git_vector_insert(&odb->backends, internal) < 0) {
+		free(internal);
 		return GIT_ENOMEM;
+	}
 
 	git_vector_sort(&odb->backends);
+	internal->backend->odb = odb;
 	return GIT_SUCCESS;
 }
 
-static int add_default_backends(git_odb *db, const char *objects_dir)
+int git_odb_add_backend(git_odb *odb, git_odb_backend *backend, int priority)
+{
+	return add_backend_internal(odb, backend, priority, 0);
+}
+
+int git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority)
+{
+	return add_backend_internal(odb, backend, priority, 1);
+}
+
+static int add_default_backends(git_odb *db, const char *objects_dir, int as_alternates)
 {
 	git_odb_backend *loose, *packed;
 	int error;
@@ -183,7 +218,7 @@ static int add_default_backends(git_odb *db, const char *objects_dir)
 	if (error < GIT_SUCCESS)
 		return error;
 
-	error = git_odb_add_backend(db, loose);
+	error = add_backend_internal(db, loose, GIT_LOOSE_PRIORITY, as_alternates);
 	if (error < GIT_SUCCESS)
 		return error;
 
@@ -192,7 +227,7 @@ static int add_default_backends(git_odb *db, const char *objects_dir)
 	if (error < GIT_SUCCESS)
 		return error;
 
-	error = git_odb_add_backend(db, packed);
+	error = add_backend_internal(db, packed, GIT_PACKED_PRIORITY, as_alternates);
 	if (error < GIT_SUCCESS)
 		return error;
 
@@ -221,7 +256,7 @@ static int load_alternates(git_odb *odb, const char *objects_dir)
 
 	/* add each alternate as a new backend; one alternate per line */
 	while ((error == GIT_SUCCESS) && (buffer = git__strtok(alternate, buffer, "\r\n")) != NULL)
-		error = add_default_backends(odb, alternate);
+		error = add_default_backends(odb, alternate, 1);
 
 	gitfo_free_buf(&alternates_buf);
 	return error;
@@ -239,7 +274,7 @@ int git_odb_open(git_odb **out, const char *objects_dir)
 	if ((error = git_odb_new(&db)) < 0)
 		return error;
 
-	if ((error = add_default_backends(db, objects_dir)) < GIT_SUCCESS)
+	if ((error = add_default_backends(db, objects_dir, 0)) < GIT_SUCCESS)
 		goto cleanup;
 
 	if ((error = load_alternates(db, objects_dir)) < GIT_SUCCESS)
@@ -261,10 +296,13 @@ void git_odb_close(git_odb *db)
 		return;
 
 	for (i = 0; i < db->backends.length; ++i) {
-		git_odb_backend *b = git_vector_get(&db->backends, i);
+		backend_internal *internal = git_vector_get(&db->backends, i);
+		git_odb_backend *backend = internal->backend;
 
-		if (b->free) b->free(b);
-		else free(b);
+		if (backend->free) backend->free(backend);
+		else free(backend);
+
+		free(internal);
 	}
 
 	git_vector_free(&db->backends);
@@ -279,7 +317,8 @@ int git_odb_exists(git_odb *db, const git_oid *id)
 	assert(db && id);
 
 	for (i = 0; i < db->backends.length && !found; ++i) {
-		git_odb_backend *b = git_vector_get(&db->backends, i);
+		backend_internal *internal = git_vector_get(&db->backends, i);
+		git_odb_backend *b = internal->backend;
 
 		if (b->exists != NULL)
 			found = b->exists(b, id);
@@ -296,7 +335,8 @@ int git_odb_read_header(git_rawobj *out, git_odb *db, const git_oid *id)
 	assert(out && db && id);
 
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
-		git_odb_backend *b = git_vector_get(&db->backends, i);
+		backend_internal *internal = git_vector_get(&db->backends, i);
+		git_odb_backend *b = internal->backend;
 
 		if (b->read_header != NULL)
 			error = b->read_header(out, b, id);
@@ -322,7 +362,8 @@ int git_odb_read(git_rawobj *out, git_odb *db, const git_oid *id)
 	assert(out && db && id);
 
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
-		git_odb_backend *b = git_vector_get(&db->backends, i);
+		backend_internal *internal = git_vector_get(&db->backends, i);
+		git_odb_backend *b = internal->backend;
 
 		if (b->read != NULL)
 			error = b->read(out, b, id);
@@ -339,7 +380,12 @@ int git_odb_write(git_oid *id, git_odb *db, git_rawobj *obj)
 	assert(obj && db && id);
 
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
-		git_odb_backend *b = git_vector_get(&db->backends, i);
+		backend_internal *internal = git_vector_get(&db->backends, i);
+		git_odb_backend *b = internal->backend;
+
+		/* we don't write in alternates! */
+		if (internal->is_alternate)
+			continue;
 
 		if (b->write != NULL)
 			error = b->write(id, b, obj);

src/odb_loose.c

@@ -653,8 +653,6 @@ int git_odb_backend_loose(git_odb_backend **backend_out, const char *objects_dir
 	backend->parent.exists = &loose_backend__exists;
 	backend->parent.free = &loose_backend__free;
 
-	backend->parent.priority = 2; /* higher than packfiles */
-
 	*backend_out = (git_odb_backend *)backend;
 	return GIT_SUCCESS;
 }

src/odb_pack.c

@@ -1203,8 +1203,6 @@ int git_odb_backend_pack(git_odb_backend **backend_out, const char *objects_dir)
 	backend->parent.exists = &pack_backend__exists;
 	backend->parent.free = &pack_backend__free;
 
-	backend->parent.priority = 1;
-
 	*backend_out = (git_odb_backend *)backend;
 	return GIT_SUCCESS;
 }

tests/t11-sqlite.c

@@ -51,7 +51,7 @@ static git_odb *open_sqlite_odb(void)
 	if (git_odb_backend_sqlite(&sqlite, ":memory") < GIT_SUCCESS)
 		return NULL;
 
-	if (git_odb_add_backend(odb, sqlite) < GIT_SUCCESS)
+	if (git_odb_add_backend(odb, sqlite, 0) < GIT_SUCCESS)
 		return NULL;
 
 	return odb;

tests/t12-repo.c

+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+#include "test_lib.h"
+#include "test_helpers.h"
+
+#include "odb.h"
+#include "git2/odb_backend.h"
+
+typedef struct {
+	git_odb_backend base;
+	int position;
+} fake_backend;
+
+git_odb_backend *new_backend(int position)
+{
+	fake_backend *b;
+
+	b = git__malloc(sizeof(fake_backend));
+	if (b == NULL)
+		return NULL;
+
+	memset(b, 0x0, sizeof(fake_backend));
+	b->position = position;
+	return (git_odb_backend *)b;
+}
+
+int test_backend_sorting(git_odb *odb)
+{
+	unsigned int i;
+
+	for (i = 0; i < odb->backends.length; ++i) {
+		fake_backend *internal = *((fake_backend **)git_vector_get(&odb->backends, i));
+
+		if (internal == NULL)
+			return GIT_ERROR;
+
+		if (internal->position != (int)i)
+			return GIT_ERROR;
+	}
+
+	return GIT_SUCCESS;
+}
+
+BEGIN_TEST("odb", backend_sorting)
+	git_odb *odb;
+	must_pass(git_odb_new(&odb));
+	must_pass(git_odb_add_backend(odb, new_backend(0), 5));
+	must_pass(git_odb_add_backend(odb, new_backend(2), 3));
+	must_pass(git_odb_add_backend(odb, new_backend(1), 4));
+	must_pass(git_odb_add_backend(odb, new_backend(3), 1));
+	must_pass(test_backend_sorting(odb));
+	git_odb_close(odb);
+END_TEST
+
+BEGIN_TEST("odb", backend_alternates_sorting)
+	git_odb *odb;
+	must_pass(git_odb_new(&odb));
+	must_pass(git_odb_add_backend(odb, new_backend(0), 5));
+	must_pass(git_odb_add_backend(odb, new_backend(2), 3));
+	must_pass(git_odb_add_backend(odb, new_backend(1), 4));
+	must_pass(git_odb_add_backend(odb, new_backend(3), 1));
+	must_pass(git_odb_add_alternate(odb, new_backend(4), 5));
+	must_pass(git_odb_add_alternate(odb, new_backend(6), 3));
+	must_pass(git_odb_add_alternate(odb, new_backend(5), 4));
+	must_pass(git_odb_add_alternate(odb, new_backend(7), 1));
+	must_pass(test_backend_sorting(odb));
+	git_odb_close(odb);
+END_TEST
+
+git_testsuite *libgit2_suite_repository(void)
+{
+	git_testsuite *suite = git_testsuite_new("Repository");
+
+	ADD_TEST(suite, "odb", backend_sorting);
+	ADD_TEST(suite, "odb", backend_alternates_sorting);
+
+	return suite;
+}

tests/test_main.c

@@ -41,6 +41,7 @@ extern git_testsuite *libgit2_suite_tag(void);
 extern git_testsuite *libgit2_suite_tree(void);
 extern git_testsuite *libgit2_suite_refs(void);
 extern git_testsuite *libgit2_suite_sqlite(void);
+extern git_testsuite *libgit2_suite_repository(void);
 
 typedef git_testsuite *(*libgit2_suite)(void);
 
@@ -57,6 +58,7 @@ static libgit2_suite suite_methods[]= {
 	libgit2_suite_tree,
 	libgit2_suite_refs,
 	libgit2_suite_sqlite,
+	libgit2_suite_repository,
 };
 
 #define GIT_SUITE_COUNT (ARRAY_SIZE(suite_methods))