odb: Direct writes are back

DIRECT WRITES ARE BACK AND FASTER THAN EVER. The streaming writer to the
ODB was an overkill for the smaller objects like Commit and Tags; most
of the streaming logic was taking too long.

This commit makes Commits, Tags and Trees to be built-up in memory, and
then written to disk in 2 pushes (header + data), instead of streaming
everything.

This is *always* faster, even for big files (since the git_filebuf class
still does streaming writes when the memory cache overflows). This is
also a gazillion lines of code smaller, because we don't have to
precompute the final size of the object before starting the stream (this
was kind of defeating the point of streaming, anyway).

Blobs are still written with full streaming instead of loading them in
memory, since this is still the fastest way.

A new `git_buf` class has been added. It's missing some features, but
it'll get there.

1 files changed, 44 insertions, 0 deletions

diff --git a/src/odb_loose.c b/src/odb_loose.c
index 2a2c464c7..a3a4e5b56 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -772,6 +772,49 @@ int loose_backend__stream(git_odb_stream **stream_out, git_odb_backend *_backend
 	return GIT_SUCCESS;
 }
 
+int loose_backend__write(git_oid *oid, git_odb_backend *_backend, const void *data, size_t len, git_otype type)
+{
+	int error, header_len;
+	char final_path[GIT_PATH_MAX], header[64];
+	git_filebuf fbuf;
+	loose_backend *backend;
+
+	backend = (loose_backend *)_backend;
+
+	/* prepare the header for the file */
+	{
+		header_len = format_object_header(header, sizeof(header), len, type);
+		if (header_len < GIT_SUCCESS)
+			return GIT_EOBJCORRUPTED;
+	}
+
+	git_path_join(final_path, backend->objects_dir, "tmp_object");
+
+	error = git_filebuf_open(&fbuf, final_path,
+		GIT_FILEBUF_HASH_CONTENTS |
+		GIT_FILEBUF_DEFLATE_CONTENTS |
+		GIT_FILEBUF_TEMPORARY);
+
+	if (error < GIT_SUCCESS)
+		return error;
+
+	git_filebuf_write(&fbuf, header, header_len);
+	git_filebuf_write(&fbuf, data, len);
+	git_filebuf_hash(oid, &fbuf);
+
+	if ((error = object_file_name(final_path, sizeof(final_path), backend->objects_dir, oid)) < GIT_SUCCESS)
+		goto cleanup;
+
+	if ((error = git_futils_mkpath2file(final_path)) < GIT_SUCCESS)
+		goto cleanup;
+
+	return git_filebuf_commit_at(&fbuf, final_path);
+
+cleanup:
+	git_filebuf_cleanup(&fbuf);
+	return error;
+}
+
 void loose_backend__free(git_odb_backend *_backend)
 {
 	loose_backend *backend;
@@ -800,6 +843,7 @@ int git_odb_backend_loose(git_odb_backend **backend_out, const char *objects_dir
 	backend->fsync_object_files = 0;
 
 	backend->parent.read = &loose_backend__read;
+	backend->parent.write = &loose_backend__write;
 	backend->parent.read_prefix = &loose_backend__read_prefix;
 	backend->parent.read_header = &loose_backend__read_header;
 	backend->parent.writestream = &loose_backend__stream;