pack-protocol.txt: accept error packets in any context

In the Git pack protocol definition, an error packet may appear only in
a certain context. However, servers can face a runtime error (e.g. I/O
error) at an arbitrary timing. This patch changes the protocol to allow
an error packet to be sent instead of any packet.

Without this protocol spec change, when a server cannot process a
request, there's no way to tell that to a client. Since the server
cannot produce a valid response, it would be forced to cut a connection
without telling why. With this protocol spec change, the server can be
more gentle in this situation. An old client may see these error packets
as an unexpected packet, but this is not worse than having an unexpected
EOF.

Following this protocol spec change, the error packet handling code is
moved to pkt-line.c. Implementation wise, this implementation uses
pkt-line to communicate with a subprocess. Since this is not a part of
Git protocol, it's possible that a packet that is not supposed to be an
error packet is mistakenly parsed as an error packet. This error packet
handling is enabled only for the Git pack protocol parsing code
considering this.

Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 10 insertions, 6 deletions

diff --git a/builtin/archive.c b/builtin/archive.c
index 2fe1f05ca2..45d11669aa 100644
--- a/builtin/archive.c
+++ b/builtin/archive.c
@@ -53,15 +53,15 @@ static int run_remote_archiver(int argc, const char **argv,
 		packet_write_fmt(fd[1], "argument %s\n", argv[i]);
 	packet_flush(fd[1]);
 
-	packet_reader_init(&reader, fd[0], NULL, 0, PACKET_READ_CHOMP_NEWLINE);
+	packet_reader_init(&reader, fd[0], NULL, 0,
+			   PACKET_READ_CHOMP_NEWLINE |
+			   PACKET_READ_DIE_ON_ERR_PACKET);
 
 	if (packet_reader_read(&reader) != PACKET_READ_NORMAL)
 		die(_("git archive: expected ACK/NAK, got a flush packet"));
 	if (strcmp(reader.line, "ACK")) {
 		if (starts_with(reader.line, "NACK "))
 			die(_("git archive: NACK %s"), reader.line + 5);
-		if (starts_with(reader.line, "ERR "))
-			die(_("remote error: %s"), reader.line + 4);
 		die(_("git archive: protocol error"));
 	}
 
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index 63e69a5801..85dbc2af87 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -217,7 +217,8 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
-			   PACKET_READ_GENTLE_ON_EOF);
+			   PACKET_READ_GENTLE_ON_EOF |
+			   PACKET_READ_DIE_ON_ERR_PACKET);
 
 	switch (discover_version(&reader)) {
 	case protocol_v2:
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 81cc073700..d58b7750b6 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1986,7 +1986,9 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 	if (advertise_refs)
 		return 0;
 
-	packet_reader_init(&reader, 0, NULL, 0, PACKET_READ_CHOMP_NEWLINE);
+	packet_reader_init(&reader, 0, NULL, 0,
+			   PACKET_READ_CHOMP_NEWLINE |
+			   PACKET_READ_DIE_ON_ERR_PACKET);
 
 	if ((commands = read_head_info(&reader, &shallow)) != NULL) {
 		const char *unpack_status = NULL;
diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index 8e3c7490f7..098ebf22d0 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -250,7 +250,8 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
 
 	packet_reader_init(&reader, fd[0], NULL, 0,
 			   PACKET_READ_CHOMP_NEWLINE |
-			   PACKET_READ_GENTLE_ON_EOF);
+			   PACKET_READ_GENTLE_ON_EOF |
+			   PACKET_READ_DIE_ON_ERR_PACKET);
 
 	switch (discover_version(&reader)) {
 	case protocol_v2: