Jeff King <peff@xxxxxxxx> writes:
> Does this patch seem otherwise worth doing?
Yeah.
FWIW, I do not find the "dependency" thing disturbing. sideband is
an extension of the pkt-line mechansim, so it is natural that it
depends on pkt-line. I'd also be happy if enums, structures and
calls defined in both headers are made available by just including
one of them (e.g. retire sideband.h, perhaps).
> An alternate patch would be to keep the behavior the same and just
> clarify the code a bit. Something like:
This also looks OK to me from readability's point of view, but it
does not as much help the end user who is puzzled as the real thing,
I am afraid.
Thanks.
> -- >8 --
> Subject: [PATCH] demultiplex_sideband(): clarify corner cases
>
> The size checks in demultiplex_sideband() are a bit subtle and
> confusing:
>
> - we consider a zero-length packet ("0004") to be a flush packet, even
> though it's not really one. This is perhaps wrong, but it should
> never happen in our protocol, and we err on the side of history and
> leniency. We'll leave a comment indicating that we expect this case.
>
> - likewise we consider any flush-like packet (e.g., "0001" delim) to
> be a flush. I didn't confirm whether this is necessary for normal
> protocol usage. It may be for the everything-over-sideband mode
> introduced by 0bbc0bc574 ({fetch,upload}-pack: sideband v2 fetch
> response, 2019-01-16). Likewise let's leave a comment.
>
> - we check for "len < 1" to see if there's no sideband designator.
> That's confusing, because we already covered the "len == 0" case.
> What is interesting is the "len < 0" case. But that's not a missing
> sideband designator, but rather an error or EOF from the pkt-line
> code. This should never happen, though, because our callers instruct
> pkt-line to die() on EOF anyway. So let's make it more obvious
> that we're looking for a negative value here, and consider it a
> BUG() in the caller to pass us garbage.
>
> Signed-off-by: Jeff King <peff@xxxxxxxx>
> ---
> sideband.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/sideband.c b/sideband.c
> index 0a60662fa6..6ba1925614 100644
> --- a/sideband.c
> +++ b/sideband.c
> @@ -130,17 +130,18 @@ int demultiplex_sideband(const char *me, char *buf, int len,
> suffix = DUMB_SUFFIX;
> }
>
> + if (len < 0)
> + BUG("error/eof packet passed to demultiplex_sideband");
> +
> if (len == 0) {
> + /*
> + * we treat all flush-like packets (flush, delim, etc) and even
> + * empty data packets as a flush
> + */
> *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;
> - }
> +
> band = buf[0] & 0xff;
> buf[len] = '\0';
> len--;
