send-pack: gracefully close the connection for atomic push

Patrick reported an issue that the exit code of git-receive-pack(1) is
ignored during atomic push with "--porcelain" flag, and added new test
cases in t5543.

This issue originated from commit 7dcbeaa (send-pack: fix
inconsistent porcelain output, 2020-04-17). At that time, I chose to
ignore the exit code of "finish_connect()" without investigating the
root cause of the abnormal termination of git-receive-pack. That was an
incorrect solution.

The root cause is that an atomic push operation terminates early without
sending a flush packet to git-receive-pack. As a result,
git-receive-pack continues waiting for commands without exiting. By
sending a flush packet at the appropriate location in "send_pack()", we
ensure that the git-receive-pack process closes properly, avoiding an
erroneous exit code for git-push. At the same time, revert the changes
to the "transport.c" file made in commit 7dcbeaa.

Reported-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jiangxin

send-pack.c

@@ -633,6 +633,7 @@ int send_pack(struct repository *r,
 				error("atomic push failed for ref %s. status: %d",
 				      ref->name, ref->status);
 				ret = ERROR_SEND_PACK_BAD_REF_STATUS;
+				packet_flush(out);
 				goto out;
 			}
 			/* else fallthrough */

t/t5543-atomic-push.sh

@@ -280,7 +280,7 @@ test_expect_success 'atomic push reports (reject by non-ff)' '
 	test_cmp expect actual
 '
 
-test_expect_failure 'atomic push reports exit code failure' '
+test_expect_success 'atomic push reports exit code failure' '
 	write_script receive-pack-wrapper <<-\EOF &&
 	git-receive-pack "$@"
 	exit 1
@@ -296,7 +296,7 @@ test_expect_failure 'atomic push reports exit code failure' '
 	test_cmp expect err
 '
 
-test_expect_failure 'atomic push reports exit code failure with porcelain' '
+test_expect_success 'atomic push reports exit code failure with porcelain' '
 	write_script receive-pack-wrapper <<-\EOF &&
 	git-receive-pack "$@"
 	exit 1

transport.c

@@ -948,15 +948,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 
 	close(data->fd[1]);
 	close(data->fd[0]);
-	/*
-	 * Atomic push may abort the connection early and close the pipe,
-	 * which may cause an error for `finish_connect()`. Ignore this error
-	 * for atomic git-push.
-	 */
-	if (ret || args.atomic)
-		finish_connect(data->conn);
-	else
-		ret = finish_connect(data->conn);
+	ret |= finish_connect(data->conn);
 	data->conn = NULL;
 	data->finished_handshake = 0;