On Tue, Oct 13, 2020 at 02:55:15PM -0400, Jeff King wrote:
> But then in fbd76cd450 (sideband: reverse its dependency on pkt-line,
> 2019-01-16), the function became demultiplex_sideband(). The loop went
> away, and we pump only a single packet on each call. When we see
> sideband 2, we do an early return. But on sideband 1, we continue to the
> cleanup: label, which flushes the scratch buffer.
>
> I think we need to return from there without hitting that cleanup label,
> like this:
By the way, the reason this works is that the "scratch" buffer persists
beyond individual calls to demultiplex_sideband(). So we can get away
with letting it persist between the two.
However unlike the original recv_sideband(), which broke out of the loop
on error and then flushed scratch, our post-fbd76cd450 does not do the
same. It now looks like:
int recv_sideband(const char *me, int in_stream, int out)
{
char buf[LARGE_PACKET_MAX + 1];
int len;
struct strbuf scratch = STRBUF_INIT;
enum sideband_type sideband_type;
while (1) {
len = packet_read(in_stream, NULL, NULL, buf, LARGE_PACKET_MAX,
0);
if (!demultiplex_sideband(me, buf, len, 0, &scratch,
&sideband_type))
continue;
switch (sideband_type) {
case SIDEBAND_PRIMARY:
write_or_die(out, buf + 1, len - 1);
break;
default: /* errors: message already written */
return sideband_type;
}
}
}
I wondered if we could ever have a case where we broke out of the loop
with data left over in "scratch" (or its buffer left allocated). I think
the answer is no. We only break out of the loop if
demultiplex_sideband() returned non-zero _and_ its not the primary
sideband. So both before and after my suggested fix, we'd have hit the
cleanup label in demultiplex_sideband(), which flushes and frees the
buffer.
I do have to say that the original loop before that commit was a lot
easier to follow, though.
Another weirdness I noticed is that it doesn't distinguish a flush
packet (expected) from a zero-byte packet (an error). But neither did
the original. I would have guessed the zero-byte packet was meant to
trigger this second conditional:
if (len == 0) {
*sideband_type = SIDEBAND_FLUSH;
goto cleanup;
}
if (len < 1) {
strbuf_addf(scratch,
"%s%s: protocol error: no band designator",
scratch->len ? "\n" : "", me);
*sideband_type = SIDEBAND_PROTOCOL_ERROR;
goto cleanup;
}
but we'd hit the first conditional before then. We would still trigger
the second if we saw EOF while reading the packet (because we set the
length to -1 then), but then it's arguably the wrong error to be
showing.
So I think this could be improved a bit by using
packet_read_with_status() in the recv_sideband() caller.
-Peff
