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, 13 insertions, 22 deletions

diff --git a/src/tree.c b/src/tree.c
index fff5068f8..ad9643f69 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -421,44 +421,35 @@ int git_treebuilder_remove(git_treebuilder *bld, const char *filename)
 
 int git_treebuilder_write(git_oid *oid, git_repository *repo, git_treebuilder *bld)
 {
-	unsigned int i, size = 0;
-	char filemode[MAX_FILEMODE_BYTES + 1 + 1];
-	git_odb_stream *stream;
+	unsigned int i;
 	int error;
+	git_buf tree = GIT_BUF_INIT;
 
 	assert(bld);
 
 	sort_entries(bld);
 
+	/* Grow the buffer beforehand to an estimated size */
+	git_buf_grow(&tree, bld->entries.length * 72);
+
 	for (i = 0; i < bld->entries.length; ++i) {
 		git_tree_entry *entry = bld->entries.contents[i];
 
 		if (entry->removed)
 			continue;
 
-		snprintf(filemode, sizeof(filemode), "%o ", entry->attr);
-		size += strlen(filemode);
-		size += entry->filename_len + 1;
-		size += GIT_OID_RAWSZ;
+		git_buf_printf(&tree, "%o ", entry->attr);
+		git_buf_put(&tree, entry->filename, entry->filename_len + 1);
+		git_buf_put(&tree, (char *)entry->oid.id, GIT_OID_RAWSZ);
 	}
 
-	if ((error = git_odb_open_wstream(&stream, git_repository_database(repo), size, GIT_OBJ_TREE)) < GIT_SUCCESS)
-		return git__rethrow(error, "Failed to write tree. Can't open write stream");
-
-	for (i = 0; i < bld->entries.length; ++i) {
-		git_tree_entry *entry = bld->entries.contents[i];
-
-		if (entry->removed)
-			continue;
-
-		snprintf(filemode, sizeof(filemode), "%o ", entry->attr);
-		stream->write(stream, filemode, strlen(filemode));
-		stream->write(stream, entry->filename, entry->filename_len + 1);
-		stream->write(stream, (char *)entry->oid.id, GIT_OID_RAWSZ);
+	if (git_buf_oom(&tree)) {
+		git_buf_free(&tree);
+		return git__throw(GIT_ENOMEM, "Not enough memory to build the tree data");
 	}
 
-	error = stream->finalize_write(oid, stream);
-	stream->free(stream);
+	error = git_odb_write(oid, git_repository_database(repo), tree.ptr, tree.size, GIT_OBJ_TREE);
+	git_buf_free(&tree);
 
 	return error == GIT_SUCCESS ? GIT_SUCCESS : git__rethrow(error, "Failed to write tree");
 }