thodg/libgit2

diff --git a/include/git2/indexer.h b/include/git2/indexer.h
index dfe6ae5..262dcd1 100644
--- a/include/git2/indexer.h
+++ b/include/git2/indexer.h
@@ -8,31 +8,11 @@
 #define _INCLUDE_git_indexer_h__
 
 #include "common.h"
+#include "types.h"
 #include "oid.h"
 
 GIT_BEGIN_DECL
 
-/**
- * This is passed as the first argument to the callback to allow the
- * user to see the progress.
- */
-typedef struct git_transfer_progress {
-	unsigned int total_objects;
-	unsigned int indexed_objects;
-	unsigned int received_objects;
-	size_t received_bytes;
-} git_transfer_progress;
-
-
-/**
- * Type for progress callbacks during indexing.  Return a value less than zero
- * to cancel the transfer.
- *
- * @param stats Structure containing information about the state of the transfer
- * @param payload Payload provided by caller
- */
-typedef int (*git_transfer_progress_callback)(const git_transfer_progress *stats, void *payload);
-
 typedef struct git_indexer_stream git_indexer_stream;
 
 /**
diff --git a/include/git2/odb.h b/include/git2/odb.h
index 8fd1a95..b64436c 100644
--- a/include/git2/odb.h
+++ b/include/git2/odb.h
@@ -10,8 +10,6 @@
 #include "common.h"
 #include "types.h"
 #include "oid.h"
-#include "odb_backend.h"
-#include "indexer.h"
 
 /**
  * @file git2/odb.h
@@ -23,6 +21,11 @@
 GIT_BEGIN_DECL
 
 /**
+ * Function type for callbacks from git_odb_foreach.
+ */
+typedef int (*git_odb_foreach_cb)(const git_oid *id, void *payload);
+
+/**
  * Create a new object database with no backends.
  *
  * Before the ODB can be used for read/writing, a custom database
@@ -53,42 +56,6 @@ GIT_EXTERN(int) git_odb_new(git_odb **out);
 GIT_EXTERN(int) git_odb_open(git_odb **out, const char *objects_dir);
 
 /**
- * Add a custom backend to an existing Object DB
- *
- * The backends are checked in relative ordering, based on the
- * value of the `priority` parameter.
- *
- * Read <odb_backends.h> for more information.
- *
- * @param odb database to add the backend to
- * @param backend pointer to a git_odb_backend instance
- * @param priority Value for ordering the backends queue
- * @return 0 on success; error code otherwise
- */
-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.
- *
- * The backends are checked in relative ordering, based on the
- * value of the `priority` parameter.
- *
- * Writing is disabled on alternate backends.
- *
- * Read <odb_backends.h> for more information.
- *
- * @param odb database to add the backend to
- * @param backend pointer to a git_odb_backend instance
- * @param priority Value for ordering the backends queue
- * @return 0 on success; error code otherwise
- */
-GIT_EXTERN(int) git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority);
-
-/**
  * Add an on-disk alternate to an existing Object DB.
  *
  * Note that the added path must point to an `objects`, not
@@ -406,6 +373,60 @@ GIT_EXTERN(size_t) git_odb_object_size(git_odb_object *object);
  */
 GIT_EXTERN(git_otype) git_odb_object_type(git_odb_object *object);
 
+/**
+ * Add a custom backend to an existing Object DB
+ *
+ * The backends are checked in relative ordering, based on the
+ * value of the `priority` parameter.
+ *
+ * Read <odb_backends.h> for more information.
+ *
+ * @param odb database to add the backend to
+ * @param backend pointer to a git_odb_backend instance
+ * @param priority Value for ordering the backends queue
+ * @return 0 on success; error code otherwise
+ */
+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.
+ *
+ * The backends are checked in relative ordering, based on the
+ * value of the `priority` parameter.
+ *
+ * Writing is disabled on alternate backends.
+ *
+ * Read <odb_backends.h> for more information.
+ *
+ * @param odb database to add the backend to
+ * @param backend pointer to a git_odb_backend instance
+ * @param priority Value for ordering the backends queue
+ * @return 0 on success; error code otherwise
+ */
+GIT_EXTERN(int) git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority);
+
+/**
+ * Get the number of ODB backend objects
+ *
+ * @param odb object database
+ * @return number of backends in the ODB
+ */
+GIT_EXTERN(size_t) git_odb_num_backends(git_odb *odb);
+
+/**
+ * Lookup an ODB backend object by index
+ *
+ * @param out output pointer to ODB backend at pos
+ * @param odb object database
+ * @param pos index into object database backend list
+ * @return 0 on success; GIT_ENOTFOUND if pos is invalid; other errors < 0
+ */
+GIT_EXTERN(int) git_odb_get_backend(git_odb_backend **out, git_odb *odb, size_t pos);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/include/git2/odb_backend.h b/include/git2/odb_backend.h
index dbc3981..d38005d 100644
--- a/include/git2/odb_backend.h
+++ b/include/git2/odb_backend.h
@@ -7,106 +7,24 @@
 #ifndef INCLUDE_git_odb_backend_h__
 #define INCLUDE_git_odb_backend_h__
 
-#include "common.h"
-#include "types.h"
-#include "oid.h"
-#include "indexer.h"
+#include "git2/common.h"
+#include "git2/types.h"
 
 /**
  * @file git2/backend.h
  * @brief Git custom backend functions
- * @defgroup git_backend Git custom backend API
+ * @defgroup git_odb Git object database routines
  * @ingroup Git
  * @{
  */
 GIT_BEGIN_DECL
 
-struct git_odb_stream;
-struct git_odb_writepack;
-
-/**
- * Function type for callbacks from git_odb_foreach.
- */
-typedef int (*git_odb_foreach_cb)(const git_oid *id, void *payload);
-
 /**
- * An instance for a custom backend
+ * Constructors for in-box ODB backends.
  */
-struct git_odb_backend {
-	unsigned int version;
-	git_odb *odb;
-
-	/* read and read_prefix each return to libgit2 a buffer which
-	 * will be freed later. The buffer should be allocated using
-	 * the function git_odb_backend_malloc to ensure that it can
-	 * be safely freed later. */
-	int (* read)(
-			void **, size_t *, git_otype *,
-			struct git_odb_backend *,
-			const git_oid *);
-
-	/* To find a unique object given a prefix
-	 * of its oid.
-	 * The oid given must be so that the
-	 * remaining (GIT_OID_HEXSZ - len)*4 bits
-	 * are 0s.
-	 */
-	int (* read_prefix)(
-			git_oid *,
-			void **, size_t *, git_otype *,
-			struct git_odb_backend *,
-			const git_oid *,
-			size_t);
-
-	int (* read_header)(
-			size_t *, git_otype *,
-			struct git_odb_backend *,
-			const git_oid *);
-
-	/* The writer may assume that the object
-	 * has already been hashed and is passed
-	 * in the first parameter.
-	 */
-	int (* write)(
-			git_oid *,
-			struct git_odb_backend *,
-			const void *,
-			size_t,
-			git_otype);
-
-	int (* writestream)(
-			struct git_odb_stream **,
-			struct git_odb_backend *,
-			size_t,
-			git_otype);
-
-	int (* readstream)(
-			struct git_odb_stream **,
-			struct git_odb_backend *,
-			const git_oid *);
-
-	int (* exists)(
-			struct git_odb_backend *,
-			const git_oid *);
-
-	int (* refresh)(struct git_odb_backend *);
-
-	int (* foreach)(
-			struct git_odb_backend *,
-			git_odb_foreach_cb cb,
-			void *payload);
-
-	int (* writepack)(
-			struct git_odb_writepack **,
-			struct git_odb_backend *,
-			git_transfer_progress_callback progress_cb,
-			void *progress_payload);
-
-	void (* free)(struct git_odb_backend *);
-};
-
-#define GIT_ODB_BACKEND_VERSION 1
-#define GIT_ODB_BACKEND_INIT {GIT_ODB_BACKEND_VERSION}
+GIT_EXTERN(int) git_odb_backend_pack(git_odb_backend **out, const char *objects_dir);
+GIT_EXTERN(int) git_odb_backend_loose(git_odb_backend **out, const char *objects_dir, int compression_level, int do_fsync);
+GIT_EXTERN(int) git_odb_backend_one_pack(git_odb_backend **out, const char *index_file);
 
 /** Streaming mode */
 enum {
@@ -117,33 +35,24 @@ enum {
 
 /** A stream to read/write from a backend */
 struct git_odb_stream {
-	struct git_odb_backend *backend;
+	git_odb_backend *backend;
 	unsigned int mode;
 
-	int (*read)(struct git_odb_stream *stream, char *buffer, size_t len);
-	int (*write)(struct git_odb_stream *stream, const char *buffer, size_t len);
-	int (*finalize_write)(git_oid *oid_p, struct git_odb_stream *stream);
-	void (*free)(struct git_odb_stream *stream);
+	int (*read)(git_odb_stream *stream, char *buffer, size_t len);
+	int (*write)(git_odb_stream *stream, const char *buffer, size_t len);
+	int (*finalize_write)(git_oid *oid_p, git_odb_stream *stream);
+	void (*free)(git_odb_stream *stream);
 };
 
 /** A stream to write a pack file to the ODB */
 struct git_odb_writepack {
-	struct git_odb_backend *backend;
+	git_odb_backend *backend;
 
-	int (*add)(struct git_odb_writepack *writepack, const void *data, size_t size, git_transfer_progress *stats);
-	int (*commit)(struct git_odb_writepack *writepack, git_transfer_progress *stats);
-	void (*free)(struct git_odb_writepack *writepack);
+	int (*add)(git_odb_writepack *writepack, const void *data, size_t size, git_transfer_progress *stats);
+	int (*commit)(git_odb_writepack *writepack, git_transfer_progress *stats);
+	void (*free)(git_odb_writepack *writepack);
 };
 
-GIT_EXTERN(void *) git_odb_backend_malloc(git_odb_backend *backend, size_t len);
-
-/**
- * Constructors for in-box ODB backends.
- */
-GIT_EXTERN(int) git_odb_backend_pack(git_odb_backend **out, const char *objects_dir);
-GIT_EXTERN(int) git_odb_backend_loose(git_odb_backend **out, const char *objects_dir, int compression_level, int do_fsync);
-GIT_EXTERN(int) git_odb_backend_one_pack(git_odb_backend **out, const char *index_file);
-
 GIT_END_DECL
 
 #endif
diff --git a/include/git2/sys/config.h b/include/git2/sys/config.h
index c9039e9..1c9deba 100644
--- a/include/git2/sys/config.h
+++ b/include/git2/sys/config.h
@@ -4,8 +4,8 @@
  * This file is part of libgit2, distributed under the GNU GPL v2 with
  * a Linking Exception. For full terms see the included COPYING file.
  */
-#ifndef INCLUDE_git_sys_config_h__
-#define INCLUDE_git_sys_config_h__
+#ifndef INCLUDE_sys_git_config_backend_h__
+#define INCLUDE_sys_git_config_backend_h__
 
 #include "git2/common.h"
 #include "git2/types.h"
@@ -14,6 +14,7 @@
 /**
  * @file git2/sys/config.h
  * @brief Git config backend routines
+ * @defgroup git_backend Git custom backend APIs
  * @ingroup Git
  * @{
  */
diff --git a/include/git2/sys/odb_backend.h b/include/git2/sys/odb_backend.h
new file mode 100644
index 0000000..3cd2734
--- /dev/null
+++ b/include/git2/sys/odb_backend.h
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_sys_git_odb_backend_h__
+#define INCLUDE_sys_git_odb_backend_h__
+
+#include "git2/common.h"
+#include "git2/types.h"
+#include "git2/oid.h"
+#include "git2/odb.h"
+
+/**
+ * @file git2/sys/backend.h
+ * @brief Git custom backend implementors functions
+ * @defgroup git_backend Git custom backend APIs
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ * An instance for a custom backend
+ */
+struct git_odb_backend {
+	unsigned int version;
+	git_odb *odb;
+
+	/* read and read_prefix each return to libgit2 a buffer which
+	 * will be freed later. The buffer should be allocated using
+	 * the function git_odb_backend_malloc to ensure that it can
+	 * be safely freed later. */
+	int (* read)(
+		void **, size_t *, git_otype *, git_odb_backend *, const git_oid *);
+
+	/* To find a unique object given a prefix
+	 * of its oid.
+	 * The oid given must be so that the
+	 * remaining (GIT_OID_HEXSZ - len)*4 bits
+	 * are 0s.
+	 */
+	int (* read_prefix)(
+		git_oid *, void **, size_t *, git_otype *,
+		git_odb_backend *, const git_oid *, size_t);
+
+	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.
+	 */
+	int (* write)(
+		git_oid *, git_odb_backend *, const void *, size_t, git_otype);
+
+	int (* writestream)(
+		git_odb_stream **, git_odb_backend *, size_t, git_otype);
+
+	int (* readstream)(
+		git_odb_stream **, git_odb_backend *, const git_oid *);
+
+	int (* exists)(
+		git_odb_backend *, const git_oid *);
+
+	int (* refresh)(git_odb_backend *);
+
+	int (* foreach)(
+		git_odb_backend *, git_odb_foreach_cb cb, void *payload);
+
+	int (* writepack)(
+		git_odb_writepack **, git_odb_backend *,
+		git_transfer_progress_callback progress_cb, void *progress_payload);
+
+	void (* free)(git_odb_backend *);
+};
+
+#define GIT_ODB_BACKEND_VERSION 1
+#define GIT_ODB_BACKEND_INIT {GIT_ODB_BACKEND_VERSION}
+
+GIT_EXTERN(void *) git_odb_backend_malloc(git_odb_backend *backend, size_t len);
+
+GIT_END_DECL
+
+#endif
diff --git a/include/git2/types.h b/include/git2/types.h
index bc15050..aca9ed9 100644
--- a/include/git2/types.h
+++ b/include/git2/types.h
@@ -196,6 +196,26 @@ typedef struct git_push git_push;
 typedef struct git_remote_head git_remote_head;
 typedef struct git_remote_callbacks git_remote_callbacks;
 
+/**
+ * This is passed as the first argument to the callback to allow the
+ * user to see the progress.
+ */
+typedef struct git_transfer_progress {
+	unsigned int total_objects;
+	unsigned int indexed_objects;
+	unsigned int received_objects;
+	size_t received_bytes;
+} git_transfer_progress;
+
+/**
+ * Type for progress callbacks during indexing.  Return a value less than zero
+ * to cancel the transfer.
+ *
+ * @param stats Structure containing information about the state of the transfer
+ * @param payload Payload provided by caller
+ */
+typedef int (*git_transfer_progress_callback)(const git_transfer_progress *stats, void *payload);
+
 /** @} */
 GIT_END_DECL
 
diff --git a/src/blob.c b/src/blob.c
index c0514fc..11e1f4d 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -8,6 +8,7 @@
 #include "git2/common.h"
 #include "git2/object.h"
 #include "git2/repository.h"
+#include "git2/odb_backend.h"
 
 #include "common.h"
 #include "blob.h"
diff --git a/src/odb.c b/src/odb.c
index c98df24..ecdaf7a 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -8,6 +8,7 @@
 #include "common.h"
 #include <zlib.h>
 #include "git2/object.h"
+#include "git2/sys/odb_backend.h"
 #include "fileops.h"
 #include "hash.h"
 #include "odb.h"
@@ -403,6 +404,27 @@ int git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority)
 	return add_backend_internal(odb, backend, priority, 1);
 }
 
+size_t git_odb_num_backends(git_odb *odb)
+{
+	assert(odb);
+	return odb->backends.length;
+}
+
+int git_odb_get_backend(git_odb_backend **out, git_odb *odb, size_t pos)
+{
+	backend_internal *internal;
+
+	assert(odb && odb);
+	internal = git_vector_get(&odb->backends, pos);
+
+	if (internal && internal->backend) {
+		*out = internal->backend;
+		return 0;
+	}
+
+	return GIT_ENOTFOUND;
+}
+
 static int add_default_backends(git_odb *db, const char *objects_dir, int as_alternates, int alternate_depth)
 {
 	git_odb_backend *loose, *packed;
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 68083f7..e78172c 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -8,7 +8,7 @@
 #include "common.h"
 #include <zlib.h>
 #include "git2/object.h"
-#include "git2/oid.h"
+#include "git2/sys/odb_backend.h"
 #include "fileops.h"
 #include "hash.h"
 #include "odb.h"
diff --git a/src/odb_pack.c b/src/odb_pack.c
index 7240a4a..773e149 100644
--- a/src/odb_pack.c
+++ b/src/odb_pack.c
@@ -8,7 +8,8 @@
 #include "common.h"
 #include <zlib.h>
 #include "git2/repository.h"
-#include "git2/oid.h"
+#include "git2/indexer.h"
+#include "git2/sys/odb_backend.h"
 #include "fileops.h"
 #include "hash.h"
 #include "odb.h"
diff --git a/src/tag.c b/src/tag.c
index 735ba7e..c82decb 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -13,6 +13,7 @@
 #include "git2/object.h"
 #include "git2/repository.h"
 #include "git2/signature.h"
+#include "git2/odb_backend.h"
 
 void git_tag__free(git_tag *tag)
 {
diff --git a/src/transports/smart_protocol.c b/src/transports/smart_protocol.c
index 8acedeb..9085198 100644
--- a/src/transports/smart_protocol.c
+++ b/src/transports/smart_protocol.c
@@ -5,6 +5,7 @@
  * a Linking Exception. For full terms see the included COPYING file.
  */
 #include "git2.h"
+#include "git2/odb_backend.h"
 
 #include "smart.h"
 #include "refs.h"
diff --git a/tests-clar/object/raw/write.c b/tests-clar/object/raw/write.c
index 1b28d0d..60aa31f 100644
--- a/tests-clar/object/raw/write.c
+++ b/tests-clar/object/raw/write.c
@@ -1,5 +1,6 @@
-
 #include "clar_libgit2.h"
+#include "git2/odb_backend.h"
+
 #include "fileops.h"
 #include "odb.h"
 
diff --git a/tests-clar/odb/packed_one.c b/tests-clar/odb/packed_one.c
index e9d246c..4f9bde9 100644
--- a/tests-clar/odb/packed_one.c
+++ b/tests-clar/odb/packed_one.c
@@ -1,5 +1,6 @@
 #include "clar_libgit2.h"
-#include "odb.h"
+#include "git2/odb_backend.h"
+
 #include "pack_data_one.h"
 #include "pack.h"
 
diff --git a/tests-clar/odb/sorting.c b/tests-clar/odb/sorting.c
index b4f9e44..147a160 100644
--- a/tests-clar/odb/sorting.c
+++ b/tests-clar/odb/sorting.c
@@ -1,13 +1,12 @@
 #include "clar_libgit2.h"
-#include "git2/odb_backend.h"
-#include "odb.h"
+#include "git2/sys/odb_backend.h"
 
 typedef struct {
 	git_odb_backend base;
-	int position;
+	size_t position;
 } fake_backend;
 
-static git_odb_backend *new_backend(int position)
+static git_odb_backend *new_backend(size_t position)
 {
 	fake_backend *b;
 
@@ -22,14 +21,13 @@ static git_odb_backend *new_backend(int position)
 
 static void check_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));
+	size_t i, max_i = git_odb_num_backends(odb);
+	fake_backend *internal;
 
+	for (i = 0; i < max_i; ++i) {
+		cl_git_pass(git_odb_get_backend((git_odb_backend **)&internal, odb, i));
 		cl_assert(internal != NULL);
-		cl_assert(internal->position == (int)i);
+		cl_assert_equal_sz(i, internal->position);
 	}
 }