[PATCH v2] upload-pack: allow shallow fetching from a read-only repository

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

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,
which mean cdab485 breaks shallow clone over git://

Fall back to $TMPDIR if $GIT_DIR/shallow_XXXXXX cannot be created in
this case. Note that in other cases that write $GIT_DIR/shallow_XXXXXX
and eventually rename it to $GIT_DIR/shallow, there is no fallback to
$TMPDIR.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Rebased on top of jk/shallow-update-fix

 builtin/receive-pack.c   |  2 +-
 commit.h                 |  2 +-
 fetch-pack.c             |  2 +-
 shallow.c                | 13 +++++++++++--
 t/t5537-fetch-shallow.sh | 13 +++++++++++++
 upload-pack.c            |  2 +-
 6 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index c323081..d723099 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -932,7 +932,7 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 			ntohl(hdr.hdr_version), ntohl(hdr.hdr_entries));
 
 	if (si->nr_ours || si->nr_theirs) {
-		alt_shallow_file = setup_temporary_shallow(si->shallow);
+		alt_shallow_file = setup_temporary_shallow(si->shallow, 0);
 		argv_array_pushl(&av, "--shallow-file", alt_shallow_file, NULL);
 	}
 
diff --git a/commit.h b/commit.h
index 55631f1..d38e996 100644
--- a/commit.h
+++ b/commit.h
@@ -209,7 +209,7 @@ extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 extern void setup_alternate_shallow(struct lock_file *shallow_lock,
 				    const char **alternate_shallow_file,
 				    const struct sha1_array *extra);
-extern const char *setup_temporary_shallow(const struct sha1_array *extra);
+extern const char *setup_temporary_shallow(const struct sha1_array *extra, int read_only);
 extern void advertise_shallow_grafts(int);
 
 struct shallow_info {
diff --git a/fetch-pack.c b/fetch-pack.c
index ae8550e..b71d186 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -853,7 +853,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 		setup_alternate_shallow(&shallow_lock, &alternate_shallow_file,
 					NULL);
 	else if (si->nr_ours || si->nr_theirs)
-		alternate_shallow_file = setup_temporary_shallow(si->shallow);
+		alternate_shallow_file = setup_temporary_shallow(si->shallow, 0);
 	else
 		alternate_shallow_file = NULL;
 	if (get_pack(args, fd, pack_lockfile))
diff --git a/shallow.c b/shallow.c
index c7602ce..ad28af6 100644
--- a/shallow.c
+++ b/shallow.c
@@ -224,7 +224,8 @@ static void remove_temporary_shallow_on_signal(int signo)
 	raise(signo);
 }
 
-const char *setup_temporary_shallow(const struct sha1_array *extra)
+const char *setup_temporary_shallow(const struct sha1_array *extra,
+				    int read_only)
 {
 	static int installed_handler;
 	struct strbuf sb = STRBUF_INIT;
@@ -235,7 +236,15 @@ const char *setup_temporary_shallow(const struct sha1_array *extra)
 
 	if (write_shallow_commits(&sb, 0, extra)) {
 		strbuf_addstr(&temporary_shallow, git_path("shallow_XXXXXX"));
-		fd = xmkstemp(temporary_shallow.buf);
+		fd = mkstemp(temporary_shallow.buf);
+		if (read_only && fd < 0) {
+			strbuf_grow(&temporary_shallow, PATH_MAX);
+			fd = git_mkstemp(temporary_shallow.buf, PATH_MAX,
+					 "shallow_XXXXXX");
+		}
+		if (fd < 0)
+			die_errno("Unable to create temporary file '%s'",
+				  temporary_shallow.buf);
 
 		if (!installed_handler) {
 			atexit(remove_temporary_shallow);
diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index b0fa738..171db88 100755
--- a/t/t5537-fetch-shallow.sh
+++ b/t/t5537-fetch-shallow.sh
@@ -173,6 +173,19 @@ EOF
 	)
 '
 
+test_expect_success POSIXPERM '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
+'
+
 if test -n "$NO_CURL" -o -z "$GIT_TEST_HTTPD"; then
 	say 'skipping remaining tests, git built without http support'
 	test_done
diff --git a/upload-pack.c b/upload-pack.c
index a3c52f6..b538f32 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -84,7 +84,7 @@ static void create_pack_file(void)
 	const char *shallow_file = NULL;
 
 	if (shallow_nr) {
-		shallow_file = setup_temporary_shallow(NULL);
+		shallow_file = setup_temporary_shallow(NULL, 1);
 		argv[arg++] = "--shallow-file";
 		argv[arg++] = shallow_file;
 	}
-- 
1.9.0.40.gaa8c3ea