Move odb_backend implementors stuff into git2/sys

This moves some of the odb_backend stuff that is related to the
internals of an odb_backend implementation into include/git2/sys.

Some of the stuff related to streaming I left in include/git2
because it seemed like it would be reasonably needed by a normal
user who wanted to stream objects into and out of the ODB.

Also, I added APIs for traversing the list of backends so that
some of the tests would not need to access ODB internals.

2 files changed, 89 insertions, 2 deletions

diff --git a/include/git2/sys/config.h b/include/git2/sys/config.h
index c9039e96e..1c9deba7c 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 000000000..3cd2734c0
--- /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