> On 27 Sep 2016, at 11:00, Jeff King <peff@xxxxxxxx> wrote: > > On Tue, Sep 27, 2016 at 10:14:16AM +0200, Lars Schneider wrote: > >>>>> + strbuf_grow(sb_out, PKTLINE_DATA_MAXLEN+1); >>>>> + paket_len = packet_read(fd_in, NULL, NULL, >>>>> + sb_out->buf + sb_out->len, PKTLINE_DATA_MAXLEN+1, options); >> [...] >> After looking at it with fresh eyes I think the existing code is probably correct, >> but maybe a bit confusing. >> >> packet_read() adds a '\0' at the end of the destination buffer: >> https://github.com/git/git/blob/21f862b498925194f8f1ebe8203b7a7df756555b/pkt-line.c#L206 >> >> That is why the destination buffer needs to be one byte larger than the expected content. >> >> However, in this particular case that wouldn't be necessary because the destination >> buffer is a 'strbuf' that allocates an extra byte for '\0' at the end. But we are not >> supposed to write to this extra byte: >> https://github.com/git/git/blob/21f862b498925194f8f1ebe8203b7a7df756555b/strbuf.h#L25-L31 > > Right. The allocation happens as part of strbuf_grow(), but whatever > fills the buffer is expected to write the actual NUL (either manually, > or by calling strbuf_setlen(). > > I see the bit you quoted warns not to touch the extra byte yourself, > though I wonder if that is a bit heavy-handed (I guess it would matter > if we moved the extra 1-byte growth into strbuf_setlen(), but I find > that a rather unlikely change). > > That being said, why don't you just use LARGE_PACKET_MAX here? It is > already the accepted size for feeding to packet_read(), and we know it > has enough space to hold a NUL terminator. Yes, we may over-allocate by > 4 bytes, but that isn't really relevant. Strbufs over-allocate anyway. TBH in that case I would prefer the "PKTLINE_DATA_MAXLEN+1" solution with an additional comment explaining "+1". Would that be OK for you? I am not worried about the extra 4 bytes. I am worried that we make it harder to see what is going on if we use LARGE_PACKET_MAX. > So just: > > for (;;) { > strbuf_grow(sb_out, LARGE_PACKET_MAX); > packet_len = packet_read(fd_in, NULL, NULL, > sb_out->buf + sb_out->len, LARGE_PACKET_MAX, > options); > if (packet_len <= 0) > break; > /* > * no need for strbuf_setlen() here; packet_read always adds a > * NUL terminator. > */ > sb_out->len += packet_len; > } > > You _could_ make the final line of the loop use strbuf_setlen(); it > would just overwrite something we already know is a NUL (and we know > that no extra allocation is necessary). > > Also, using LARGE_PACKET_MAX fixes the fact that this patch is using > PKTLINE_DATA_MAXLEN before it is actually defined. :) Yeah, I noticed that too and fixed it in v9 :-) Thanks for the reminder! > You might want to occasionally run: > > git rebase -x make > > to make sure all of your incremental steps are valid (or even "make > test" if you are extremely patient; I often do that once after a big > round of complex interactive-rebase reordering). That is a good suggestion. I'll add that to my "tool-belt" :-) Thanks, Lars