On Fri, Jul 03, 2015 at 10:45:59AM -0700, Junio C Hamano wrote:
> > Usually flush packets are "0000", and an empty data packet
> > is "0004". Or are you talking about some kind of flush inside the
> > pkt-data stream?
>
> Neither. At the wire level there is a difference, but the callers
> of most often used function in pkt-line API, packet_read(), says
>
> while (1) {
> len = packet_read();
> if (!len) {
> /* flush */
> break;
> }
> ... do things on the "len" bytes received ...
> ... and then on to the next packet ...
> }
Ah, I see. Yeah, that is a problem. The solutions you proposed seem like
good workarounds to me, but we are unfortunately stuck with existing
clients and servers which did not behave that way.
I wondered briefly whether this impacted the keepalives we added to
`upload-pack` in 05e9515; those are implemented as 0-byte data packets,
which we send during the potentially long counting/delta-compression
phase before we send out pack data. It works there because the packets
actually contain a single sideband byte, so they are never mistaken for
a flush packet.
Related, I recently ran into a case where I think we should do the same
for pushes. After receiving the pack, `index-pack` may chew on the
result for literally minutes (try pushing up the entire linux.git
history sometime). We say nothing at all on the wire until we've
finished that, run check_everything_connected, and run all hooks. Some
clients (or intermediates on the connection) may give up after a few
minutes of silence.
I think we should have:
1. Some progress eye-candy from the server to tell us that something
is happening, and how close we are to finishing (basically
"index-pack -v").
2. When progress is disabled, similar keepalive packets saying "nope,
no output yet".
For (2), hopefully we can implement it in the same way, and rely on
empty sideband-0 packets. I haven't tested it in practice, though (I
have some very rough patches for (1) already).
-Peff
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