[RFC PATCH] receive-pack: run post-receive before reporting status

[Robin Jarry <robin.jarry@6wind.com>]

When a remote client exits while the pre-receive hook is running,
receive-pack is not killed by SIGPIPE because the signal is ignored.
This is a side effect of commit ec7dbd145bd8 ("receive-pack: allow hooks
to ignore its standard input stream").

The pre-receive hook is not interrupted and does not receive any error
since its stdout is a pipe which is read in an async thread and output
back to the client socket in a side band channel. When writing the data
in the socket, the async thread gets a SIGPIPE which also seems ignored.
This may be a race between the main and the async threads. I do not know
the code well enough to be sure.

After the pre-receive has exited the SIGPIPE default handler is restored
and if the hook did not report any error, objects are migrated from
temporary to permanent storage.

Before running the post-receive hook, status info is reported back to
the client. Since the client has died, receive-pack is killed by SIGPIPE
and post-receive is never executed.

The post-receive hook is often used to send email notifications (see
contrib/hooks/post-receive-email), update bug trackers, start automatic
builds, etc. Not executing it after an interrupted yet "successful" push
can lead to inconsistencies.

Execute the post-receive hook before reporting status to the client to
avoid this issue. This is not an ideal solution but I don't know if
allowing hooks to be killed when a client exits is a good idea. Maybe
for pre-receive but definitely not for post-receive.

Signed-off-by: Robin Jarry <robin.jarry@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 builtin/receive-pack.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 49b846d96052..df8bedf71319 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -2564,14 +2564,14 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 		use_keepalive = KEEPALIVE_ALWAYS;
 		execute_commands(commands, unpack_status, &si,
 				 &push_options);
+		run_receive_hook(commands, "post-receive", 1,
+				 &push_options);
 		if (pack_lockfile)
 			unlink_or_warn(pack_lockfile);
 		if (report_status_v2)
 			report_v2(commands, unpack_status);
 		else if (report_status)
 			report(commands, unpack_status);
-		run_receive_hook(commands, "post-receive", 1,
-				 &push_options);
 		run_update_post_hook(commands);
 		string_list_clear(&push_options, 0);
 		if (auto_gc) {
-- 
2.30.2