allow OFS_DELTA objects during a push

The fetching of OFS_DELTA objects has been negotiated between both peers
since git version 1.4.4.  However, this was missing from the push side
where every OFS_DELTA objects were always converted to REF_DELTA objects
causing an increase in transferred data.

To fix this, both the client and the server processes have to be
modified: the former to invoke pack-objects with --delta-base-offset
when the server provides the ofs-delta capability, and the later to send
that capability when OFS_DELTA objects are allowed as already indicated
by the repack.usedeltabaseoffset config variable which is TRUE by
default since git v1.6.0.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-receive-pack.c

@@ -27,10 +27,9 @@ static int receive_unpack_limit = -1;
 static int transfer_unpack_limit = -1;
 static int unpack_limit = 100;
 static int report_status;
+static int prefer_ofs_delta = 1;
 static const char *head_name;
-
-static char capabilities[] = " report-status delete-refs ";
-static int capabilities_sent;
+static char *capabilities_to_send;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
 {
@@ -84,24 +83,29 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (strcmp(var, "repack.usedeltabaseoffset") == 0) {
+		prefer_ofs_delta = git_config_bool(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
 static int show_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
 {
-	if (capabilities_sent)
+	if (!capabilities_to_send)
 		packet_write(1, "%s %s\n", sha1_to_hex(sha1), path);
 	else
 		packet_write(1, "%s %s%c%s\n",
-			     sha1_to_hex(sha1), path, 0, capabilities);
-	capabilities_sent = 1;
+			     sha1_to_hex(sha1), path, 0, capabilities_to_send);
+	capabilities_to_send = NULL;
 	return 0;
 }
 
 static void write_head_info(void)
 {
 	for_each_ref(show_ref, NULL);
-	if (!capabilities_sent)
+	if (capabilities_to_send)
 		show_ref("capabilities^{}", null_sha1, 0, NULL);
 
 }
@@ -687,6 +691,10 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 	else if (0 <= receive_unpack_limit)
 		unpack_limit = receive_unpack_limit;
 
+	capabilities_to_send = (prefer_ofs_delta) ?
+		" report-status delete-refs ofs-delta " :
+		" report-status delete-refs ";
+
 	add_alternate_refs();
 	write_head_info();
 	clear_extra_refs();

builtin-send-pack.c

@@ -43,12 +43,16 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
 		"--stdout",
 		NULL,
 		NULL,
+		NULL,
 	};
 	struct child_process po;
 	int i;
 
+	i = 4;
 	if (args->use_thin_pack)
-		argv[4] = "--thin";
+		argv[i++] = "--thin";
+	if (args->use_ofs_delta)
+		argv[i++] = "--delta-base-offset";
 	memset(&po, 0, sizeof(po));
 	po.argv = argv;
 	po.in = -1;
@@ -315,6 +319,8 @@ int send_pack(struct send_pack_args *args,
 		ask_for_status_report = 1;
 	if (server_supports("delete-refs"))
 		allow_deleting_refs = 1;
+	if (server_supports("ofs-delta"))
+		args->use_ofs_delta = 1;
 
 	if (!remote_refs) {
 		fprintf(stderr, "No refs in common and none specified; doing nothing.\n"

send-pack.h

@@ -6,6 +6,7 @@ struct send_pack_args {
 		send_mirror:1,
 		force_update:1,
 		use_thin_pack:1,
+		use_ofs_delta:1,
 		dry_run:1;
 };