fetch-pack: write fetched refs to .promisor

The specification of promisor packfiles (in partial-clone.txt) states
that the .promisor files that accompany packfiles do not matter (just
like .keep files), so whenever a packfile is fetched from the promisor
remote, Git has been writing empty .promisor files. But these files
could contain more useful information.

So instead of writing empty files, write the refs fetched to these
files. This makes it easier to debug issues with partial clones, as we
can identify what refs (and their associated hashes) were fetched at the
time the packfile was downloaded, and if necessary, compare those hashes
against what the promisor remote reports now.

This is implemented by teaching fetch-pack to write its own non-empty
.promisor file whenever it knows the name of the pack's lockfile. This
covers the case wherein the user runs "git fetch" with an internal
protocol or HTTP protocol v2 (fetch_refs_via_pack() in transport.c sets
lock_pack) and with HTTP protocol v0/v1 (fetch_git() in remote-curl.c
passes "--lock-pack" to "fetch-pack").

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Acked-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 43 insertions, 4 deletions

diff --git a/fetch-pack.c b/fetch-pack.c
index 947da545de..b9e63b52ff 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -754,8 +754,33 @@ static int sideband_demux(int in, int out, void *data)
 	return ret;
 }
 
+static void write_promisor_file(const char *keep_name,
+				struct ref **sought, int nr_sought)
+{
+	struct strbuf promisor_name = STRBUF_INIT;
+	int suffix_stripped;
+	FILE *output;
+	int i;
+
+	strbuf_addstr(&promisor_name, keep_name);
+	suffix_stripped = strbuf_strip_suffix(&promisor_name, ".keep");
+	if (!suffix_stripped)
+		BUG("name of pack lockfile should end with .keep (was '%s')",
+		    keep_name);
+	strbuf_addstr(&promisor_name, ".promisor");
+
+	output = xfopen(promisor_name.buf, "w");
+	for (i = 0; i < nr_sought; i++)
+		fprintf(output, "%s %s\n", oid_to_hex(&sought[i]->old_oid),
+			sought[i]->name);
+	fclose(output);
+
+	strbuf_release(&promisor_name);
+}
+
 static int get_pack(struct fetch_pack_args *args,
-		    int xd[2], char **pack_lockfile)
+		    int xd[2], char **pack_lockfile,
+		    struct ref **sought, int nr_sought)
 {
 	struct async demux;
 	int do_keep = args->keep_pack;
@@ -817,7 +842,13 @@ static int get_pack(struct fetch_pack_args *args,
 		}
 		if (args->check_self_contained_and_connected)
 			argv_array_push(&cmd.args, "--check-self-contained-and-connected");
-		if (args->from_promisor)
+		/*
+		 * If we're obtaining the filename of a lockfile, we'll use
+		 * that filename to write a .promisor file with more
+		 * information below. If not, we need index-pack to do it for
+		 * us.
+		 */
+		if (!(do_keep && pack_lockfile) && args->from_promisor)
 			argv_array_push(&cmd.args, "--promisor");
 	}
 	else {
@@ -871,6 +902,14 @@ static int get_pack(struct fetch_pack_args *args,
 		die(_("%s failed"), cmd_name);
 	if (use_sideband && finish_async(&demux))
 		die(_("error in sideband demultiplexer"));
+
+	/*
+	 * Now that index-pack has succeeded, write the promisor file using the
+	 * obtained .keep filename if necessary
+	 */
+	if (do_keep && pack_lockfile && args->from_promisor)
+		write_promisor_file(*pack_lockfile, sought, nr_sought);
+
 	return 0;
 }
 
@@ -1006,7 +1045,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 		alternate_shallow_file = setup_temporary_shallow(si->shallow);
 	else
 		alternate_shallow_file = NULL;
-	if (get_pack(args, fd, pack_lockfile))
+	if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
 		die(_("git fetch-pack: fetch failed."));
 
  all_done:
@@ -1453,7 +1492,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 
 			/* get the pack */
 			process_section_header(&reader, "packfile", 0);
-			if (get_pack(args, fd, pack_lockfile))
+			if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
 				die(_("git fetch-pack: fetch failed."));
 
 			state = FETCH_DONE;