upload-pack: send shallow info over stdin to pack-objects

Before cdab485 (upload-pack: delegate rev walking in shallow fetch to
pack-objects - 2013-08-16) upload-pack does not write to the source
repository. cdab485 starts to write $GIT_DIR/shallow_XXXXXX if it's a
shallow fetch, so the source repo must be writable.

git:// servers do not need write access to repos and usually don't
have it, which means cdab485 breaks shallow clone over git://

Instead of using a temporary file as the media for shallow points, we
can send them over stdin to pack-objects as well. Prepend shallow
SHA-1 with --shallow so pack-objects knows what is what.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-pack-objects.txt

@@ -64,6 +64,8 @@ base-name::
 	the same way as 'git rev-list' with the `--objects` flag
 	uses its `commit` arguments to build the list of objects it
 	outputs.  The objects on the resulting list are packed.
+	Besides revisions, `--not` or `--shallow <SHA-1>` lines are
+	also accepted.
 
 --unpacked::
 	This implies `--revs`.  When processing the list of

builtin/pack-objects.c

@@ -2358,6 +2358,9 @@ static void get_object_list(int ac, const char **av)
 	save_commit_buffer = 0;
 	setup_revisions(ac, av, &revs, NULL);
 
+	/* make sure shallows are read */
+	is_repository_shallow();
+
 	while (fgets(line, sizeof(line), stdin) != NULL) {
 		int len = strlen(line);
 		if (len && line[len - 1] == '\n')
@@ -2369,6 +2372,13 @@ static void get_object_list(int ac, const char **av)
 				flags ^= UNINTERESTING;
 				continue;
 			}
+			if (starts_with(line, "--shallow ")) {
+				unsigned char sha1[20];
+				if (get_sha1_hex(line + 10, sha1))
+					die("not an SHA-1 '%s'", line + 10);
+				register_shallow(sha1);
+				continue;
+			}
 			die("not a rev '%s'", line);
 		}
 		if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))

t/t5537-fetch-shallow.sh

@@ -200,5 +200,18 @@ EOF
 	)
 '
 
+test_expect_success POSIXPERM,SANITY 'shallow fetch from a read-only repo' '
+	cp -R .git read-only.git &&
+	find read-only.git -print | xargs chmod -w &&
+	test_when_finished "find read-only.git -type d -print | xargs chmod +w" &&
+	git clone --no-local --depth=2 read-only.git from-read-only &&
+	git --git-dir=from-read-only/.git log --format=%s >actual &&
+	cat >expect <<EOF &&
+add-1-back
+4
+EOF
+	test_cmp expect actual
+'
+
 stop_httpd
 test_done

upload-pack.c

@@ -70,6 +70,14 @@ static ssize_t send_client_data(int fd, const char *data, ssize_t sz)
 	return sz;
 }
 
+static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
+{
+	FILE *fp = cb_data;
+	if (graft->nr_parent == -1)
+		fprintf(fp, "--shallow %s\n", sha1_to_hex(graft->sha1));
+	return 0;
+}
+
 static void create_pack_file(void)
 {
 	struct child_process pack_objects;
@@ -81,12 +89,10 @@ static void create_pack_file(void)
 	const char *argv[12];
 	int i, arg = 0;
 	FILE *pipe_fd;
-	char *shallow_file = NULL;
 
 	if (shallow_nr) {
-		shallow_file = setup_temporary_shallow(NULL);
 		argv[arg++] = "--shallow-file";
-		argv[arg++] = shallow_file;
+		argv[arg++] = "";
 	}
 	argv[arg++] = "pack-objects";
 	argv[arg++] = "--revs";
@@ -114,6 +120,9 @@ static void create_pack_file(void)
 
 	pipe_fd = xfdopen(pack_objects.in, "w");
 
+	if (shallow_nr)
+		for_each_commit_graft(write_one_shallow, pipe_fd);
+
 	for (i = 0; i < want_obj.nr; i++)
 		fprintf(pipe_fd, "%s\n",
 			sha1_to_hex(want_obj.objects[i].item->sha1));
@@ -242,12 +251,6 @@ static void create_pack_file(void)
 		error("git upload-pack: git-pack-objects died with error.");
 		goto fail;
 	}
-	if (shallow_file) {
-		if (*shallow_file)
-			unlink(shallow_file);
-		free(shallow_file);
-	}
-
 	/* flush the data */
 	if (0 <= buffered) {
 		data[0] = buffered;