path: root/Documentation/technical/pack-protocol.txt
diff options
authorMasaya Suzuki <>2018-12-29 21:19:15 (GMT)
committerJunio C Hamano <>2019-01-02 21:05:30 (GMT)
commit2d103c31c2cfcf03ff1408d639043469b0c93f70 (patch)
tree17a4e7a35fb5401fad2b8713e17360af0573682e /Documentation/technical/pack-protocol.txt
parent01f9ec64c8a82a05ba7e5a17b292ede037a469ea (diff)
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 <> Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'Documentation/technical/pack-protocol.txt')
1 files changed, 11 insertions, 9 deletions
diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index 6ac774d..7a2375a 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -22,6 +22,16 @@ protocol-common.txt. When the grammar indicate `PKT-LINE(...)`, unless
otherwise noted the usual pkt-line LF rules apply: the sender SHOULD
include a LF, but the receiver MUST NOT complain if it is not present.
+An error packet is a special pkt-line that contains an error string.
+ error-line = PKT-LINE("ERR" SP explanation-text)
+Throughout the protocol, where `PKT-LINE(...)` is expected, an error packet MAY
+be sent. Once this packet is sent by a client or a server, the data transfer
+process defined in this protocol is terminated.
There are three transports over which the packfile protocol is
@@ -89,13 +99,6 @@ process on the server side over the Git protocol is this:
"0039git-upload-pack /schacon/gitbook.git\\0" |
nc -v 9418
-If the server refuses the request for some reasons, it could abort
-gracefully with an error message.
- error-line = PKT-LINE("ERR" SP explanation-text)
SSH Transport
@@ -398,12 +401,11 @@ from the client).
Then the server will start sending its packfile data.
- server-response = *ack_multi ack / nak / error-line
+ server-response = *ack_multi ack / nak
ack_multi = PKT-LINE("ACK" SP obj-id ack_status)
ack_status = "continue" / "common" / "ready"
ack = PKT-LINE("ACK" SP obj-id)
nak = PKT-LINE("NAK")
- error-line = PKT-LINE("ERR" SP explanation-text)
A simple clone may look like this (with no 'have' lines):