Merge pull request #2208 from libgit2/vmg/mempack

In-memory packing backend

2 files changed, 96 insertions, 0 deletions

diff --git a/include/git2/pack.h b/include/git2/pack.h
index 11bb559d8..29c926c65 100644
--- a/include/git2/pack.h
+++ b/include/git2/pack.h
@@ -115,6 +115,17 @@ GIT_EXTERN(int) git_packbuilder_insert_tree(git_packbuilder *pb, const git_oid *
 GIT_EXTERN(int) git_packbuilder_insert_commit(git_packbuilder *pb, const git_oid *id);
 
 /**
+ * Write the contents of the packfile to an in-memory buffer
+ *
+ * The contents of the buffer will become a valid packfile, even though there
+ * will be no attached index
+ *
+ * @param buf Buffer where to write the packfile
+ * @param pb The packbuilder
+ */
+GIT_EXTERN(int) git_packbuilder_write_buf(git_buf *buf, git_packbuilder *pb);
+
+/**
  * Write the new pack and corresponding index file to path.
  *
  * @param pb The packbuilder
diff --git a/include/git2/sys/mempack.h b/include/git2/sys/mempack.h
new file mode 100644
index 000000000..d3bc87b4d
--- /dev/null
+++ b/include/git2/sys/mempack.h
@@ -0,0 +1,85 @@
+/*
+ * 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_mempack_h__
+#define INCLUDE_sys_git_odb_mempack_h__
+
+#include "git2/common.h"
+#include "git2/types.h"
+#include "git2/oid.h"
+#include "git2/odb.h"
+
+/**
+ * @file git2/sys/mempack.h
+ * @brief Custom ODB backend that permits packing objects in-memory
+ * @defgroup git_backend Git custom backend APIs
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ *	Instantiate a new mempack backend.
+ *
+ *	The backend must be added to an existing ODB with the highest
+ *	priority.
+ *
+ *		git_mempack_new(&mempacker);
+ *		git_repository_odb(&odb, repository);
+ *		git_odb_add_backend(odb, mempacker, 999);
+ *
+ *	Once the backend has been loaded, all writes to the ODB will
+ *	instead be queued in memory, and can be finalized with
+ *	`git_mempack_dump`.
+ *
+ *	Subsequent reads will also be served from the in-memory store
+ *	to ensure consistency, until the memory store is dumped.
+ *
+ *	@param out Poiter where to store the ODB backend
+ *	@return 0 on success; error code otherwise
+ */
+int git_mempack_new(git_odb_backend **out);
+
+/**
+ *	Dump all the queued in-memory writes to a packfile.
+ *
+ *	The contents of the packfile will be stored in the given buffer.
+ *	It is the caller's responsability to ensure that the generated
+ *	packfile is available to the repository (e.g. by writing it
+ *	to disk, or doing something crazy like distributing it across
+ *	several copies of the repository over a network).
+ *
+ *	Once the generated packfile is available to the repository,
+ *	call `git_mempack_reset` to cleanup the memory store.
+ *
+ *	Calling `git_mempack_reset` before the packfile has been
+ *	written to disk will result in an inconsistent repository
+ *	(the objects in the memory store won't be accessible).
+ *
+ *	@param pack Buffer where to store the raw packfile
+ *	@param repo The active repository where the backend is loaded
+ *	@param backend The mempack backend
+ *	@return 0 on success; error code otherwise
+ */
+int git_mempack_dump(git_buf *pack, git_repository *repo, git_odb_backend *backend);
+
+/**
+ *	Reset the memory packer by clearing all the queued objects.
+ *
+ *	This assumes that `git_mempack_dump` has been called before to
+ *	store all the queued objects into a single packfile.
+ *
+ *	Alternatively, call `reset` without a previous dump to "undo"
+ *	all the recently written objects, giving transaction-like
+ *	semantics to the Git repository.
+ *
+ *	@param backend The mempack backend
+ */
+void git_mempack_reset(git_odb_backend *backend);
+
+GIT_END_DECL
+
+#endif