From d415092ac4a7fb474dc9823a1cc08ae824267e35 Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Fri, 15 Jul 2016 06:36:14 -0400
Subject: receive-pack: relay connectivity errors to sideband

If the connectivity check encounters a problem when
receiving a push, the error output goes to receive-pack's
stderr, whose destination depends on the protocol used
(ssh tends to send it to the user, though without a "remote"
prefix; http will generally eat it in the server's error
log).

The information should consistently go back to the user, as
there is a reasonable chance their client is buggy and
generating a bad pack.

We can do so by muxing it over the sideband as we do with
other sub-process stderr.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index de322bc..d309109 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1317,9 +1317,12 @@ static void execute_commands(struct command *commands,
 			     const char *unpacker_error,
 			     struct shallow_info *si)
 {
+	struct check_connected_options opt = CHECK_CONNECTED_INIT;
 	struct command *cmd;
 	unsigned char sha1[20];
 	struct iterate_data data;
+	struct async muxer;
+	int err_fd = 0;
 
 	if (unpacker_error) {
 		for (cmd = commands; cmd; cmd = cmd->next)
@@ -1327,11 +1330,24 @@ 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 */
+	}
+
 	data.cmds = commands;
 	data.si = si;
-	if (check_connected(iterate_receive_command_list, &data, NULL))
+	opt.err_fd = err_fd;
+	if (check_connected(iterate_receive_command_list, &data, &opt))
 		set_connectivity_errors(commands, si);
 
+	if (use_sideband)
+		finish_async(&muxer);
+
 	reject_updates_to_hidden(commands);
 
 	if (run_receive_hook(commands, "pre-receive", 0)) {
-- 
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