[RFC PATCH 2/2] builtin/receive-pack: add option to skip connectivity check

[Justin Tobler <jltobler@gmail.com>]

During git-receive-pack(1), connectivity of the object graph is
validated to ensure that the received packfile does not leave the
repository in a broken state.

Generally, this check is critical to avoid an incomplete receieved
packfile from corrupting a repository. In situations where server
operators validate the connectivity of incoming objects outside of Git,
such a check may be redundant.

Introduce the --skip-connectivity-check option for git-receive-pack(1)
which bypasses this connectivity check to give more control to on the
server-side.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
---
 builtin/receive-pack.c  | 40 ++++++++++++++++++++++------------------
 t/t5412-receive-pack.sh | 20 ++++++++++++++++++++
 2 files changed, 42 insertions(+), 18 deletions(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index be314879e8..66674bc408 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -81,6 +81,7 @@ static int prefer_ofs_delta = 1;
 static int auto_update_server_info;
 static int auto_gc = 1;
 static int reject_thin;
+static int skip_connectivity_check;
 static int stateless_rpc;
 static const char *service_dir;
 static const char *head_name;
@@ -1936,27 +1937,29 @@ static void execute_commands(struct command *commands,
 		return;
 	}
 
-	if (use_sideband) {
-		memset(&muxer, 0, sizeof(muxer));
-		muxer.proc = copy_to_sideband;
-		muxer.in = -1;
-		if (!start_async(&muxer))
-			err_fd = muxer.in;
-		/* ...else, continue without relaying sideband */
-	}
+	if (!skip_connectivity_check) {
+		if (use_sideband) {
+			memset(&muxer, 0, sizeof(muxer));
+			muxer.proc = copy_to_sideband;
+			muxer.in = -1;
+			if (!start_async(&muxer))
+				err_fd = muxer.in;
+			/* ...else, continue without relaying sideband */
+		}
 
-	data.cmds = commands;
-	data.si = si;
-	opt.err_fd = err_fd;
-	opt.progress = err_fd && !quiet;
-	opt.env = tmp_objdir_env(tmp_objdir);
-	opt.exclude_hidden_refs_section = "receive";
+		data.cmds = commands;
+		data.si = si;
+		opt.err_fd = err_fd;
+		opt.progress = err_fd && !quiet;
+		opt.env = tmp_objdir_env(tmp_objdir);
+		opt.exclude_hidden_refs_section = "receive";
 
-	if (check_connected(iterate_receive_command_list, &data, &opt))
-		set_connectivity_errors(commands, si);
+		if (check_connected(iterate_receive_command_list, &data, &opt))
+			set_connectivity_errors(commands, si);
 
-	if (use_sideband)
-		finish_async(&muxer);
+		if (use_sideband)
+			finish_async(&muxer);
+	}
 
 	reject_updates_to_hidden(commands);
 
@@ -2517,6 +2520,7 @@ int cmd_receive_pack(int argc,
 
 	struct option options[] = {
 		OPT__QUIET(&quiet, N_("quiet")),
+		OPT_HIDDEN_BOOL(0, "skip-connectivity-check", &skip_connectivity_check, NULL),
 		OPT_HIDDEN_BOOL(0, "stateless-rpc", &stateless_rpc, NULL),
 		OPT_HIDDEN_BOOL(0, "http-backend-info-refs", &advertise_refs, NULL),
 		OPT_ALIAS(0, "advertise-refs", "http-backend-info-refs"),
diff --git a/t/t5412-receive-pack.sh b/t/t5412-receive-pack.sh
index 190c7d3624..426a3a3df4 100755
--- a/t/t5412-receive-pack.sh
+++ b/t/t5412-receive-pack.sh
@@ -24,4 +24,24 @@ test_expect_success 'receive-pack missing objects fails connectivity check' '
 	test_must_fail git -C remote.git cat-file -e $(git -C repo rev-parse HEAD)
 '
 
+test_expect_success 'receive-pack missing objects bypasses connectivity check' '
+	test_when_finished rm -rf repo remote.git setup.git &&
+
+	git init repo &&
+	git -C repo commit --allow-empty -m 1 &&
+	git clone --bare repo setup.git &&
+	git -C repo commit --allow-empty -m 2 &&
+
+	# Capture git-send-pack(1) output sent to git-receive-pack(1).
+	git -C repo send-pack ../setup.git --all \
+		--receive-pack="tee ${SQ}$(pwd)/out${SQ} | git-receive-pack" &&
+
+	# Replay captured git-send-pack(1) output on new empty repository.
+	git init --bare remote.git &&
+	git receive-pack --skip-connectivity-check remote.git <out >actual &&
+
+	test_grep ! "fatal: Failed to traverse parents" actual &&
+	git -C remote.git cat-file -e $(git -C repo rev-parse HEAD)
+'
+
 test_done
-- 
2.49.0.111.g5b97a56fa0