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Re: [PATCH 3/4] strbuf: introduce `strbuf_attachstr()`

From
MÅMartin Ågren <martin.agren@gmail.com>
Date
Apr 21, 2020, 18:47 UTC
Message-ID
<CAN0heSp3KWU8Q8_+-GPUePfQorbyWdwm-eo4eGBRcnTtxOvS4A@mail.gmail.com>
In-Reply-To
<xmqqzhb6q74r.fsf@gitster.c.googlers.com>
On Mon, 20 Apr 2020 at 21:39, Junio C Hamano <gitster@pobox.com> wrote:
Show 20 quoted lines
>
> Martin Ågren <martin.agren@gmail.com> writes:
>
> > +/**
> > + * Attach a string to a buffer similar to `strbuf_attachstr_len()`.
> > + * Useful if you do not know the length of the string.
> > + */
> > +static inline void strbuf_attachstr(struct strbuf *sb, char *str)
> > +{
> > +     size_t len = strlen(str);
> > +
> > +     strbuf_attach(sb, str, len, len + 1);
> > +}
>
> This is somewhat worrysome in that the interface is _so_ simple that
> people may fail to see that str must be allocated piece of memory,
> and it is preferrable if string fully fills the allocation.
>
> We should repeat that (instead of just trusting "similar to ..."
> would tell them enough) in the doc, perhaps?

Yeah, that's a good point. I'll expand on this to try to better get through that there are things to consider here.

Show 14 quoted lines
> > @@ -1095,7 +1095,7 @@ void trailer_info_get(struct trailer_info *info, const char *str,
> >       for (ptr = trailer_lines; *ptr; ptr++) {
> >               if (last && isspace((*ptr)->buf[0])) {
> >                       struct strbuf sb = STRBUF_INIT;
> > -                     strbuf_attach(&sb, *last, strlen(*last), strlen(*last));
> > +                     strbuf_attachstr(&sb, *last);
> >                       strbuf_addbuf(&sb, *ptr);
> >                       *last = strbuf_detach(&sb, NULL);
> >                       continue;
>
> This is not wrong per-se, but it is unclear if use of strbuf_attach*
> family to avoid an explicit malloc/copy/free is buying much at this
> callsite.  Simplifying the code here of course is not within the
> scope of this series.

For the other patches in this series, I spent some time and effort investigating where strings came from, "do I really feel certain that they're NUL-terminated?". But for this patch, I more or less went "we've been using strlen on this all this time, surely if it wasn't guaranteed to be NUL-terminated we'd have messed up already". And I don't think I'm making anything worse. But yeah, I didn't really step back to look at what these sites are really doing, and how, as much as I did for the others.

Martin
Previous: Junio C HamanoNext: Martin Ågren
Message 18 of 39 in “mailinfo.c::convert_to_utf8: reuse strlen info”
  1. mailinfo.c::convert_to_utf8: reuse strlen infoĐoàn Trần Công Danh, Apr 18, 2020
  2. Martin ÅgrenApr 18, 2020
  3. 0/6 strbuf: simplify `strbuf_attach()` usageMartin Ågren, Apr 18, 2020
  4. 1/6 am: use `strbuf_attach()` correctlyMartin Ågren, Apr 18, 2020
  5. 2/6 strbuf_attach: correctly pass in `strlen() + 1` for `alloc`Martin Ågren, Apr 18, 2020
  6. 3/6 strbuf: use `strbuf_attach()` correctlyMartin Ågren, Apr 18, 2020
  7. 4/6 fast-import: avoid awkward use of `strbuf_attach()`Martin Ågren, Apr 18, 2020
  8. 5/6 rerere: avoid awkward use of `strbuf_attach()`Martin Ågren, Apr 18, 2020
  9. 6/6 strbuf: simplify `strbuf_attach()` usageMartin Ågren, Apr 18, 2020
  10. Martin ÅgrenApr 19, 2020
  11. 0/4 strbuf: fix doc for `strbuf_attach()` and avoid itMartin Ågren, Apr 19, 2020
  12. 1/4 strbuf: fix doc for `strbuf_attach()`Martin Ågren, Apr 19, 2020
  13. Junio C HamanoApr 20, 2020
  14. Martin ÅgrenApr 21, 2020
  15. 2/4 strbuf: introduce `strbuf_attachstr_len()`Martin Ågren, Apr 19, 2020
  16. 3/4 strbuf: introduce `strbuf_attachstr()`Martin Ågren, Apr 19, 2020
  17. Junio C HamanoApr 20, 2020
  18. Martin ÅgrenApr 21, 2020
  19. 4/4 strbuf_attach: prefer `strbuf_attachstr_len()`Martin Ågren, Apr 19, 2020
  20. Junio C HamanoApr 18, 2020
  21. Danh DoanApr 19, 2020
  22. Martin ÅgrenApr 19, 2020
  23. Junio C HamanoApr 19, 2020
  24. 0/3 mailinfo: disallow and complains about NUL characterĐoàn Trần Công Danh, Apr 19, 2020
  25. 1/3 t4254: merge 2 steps of a single testĐoàn Trần Công Danh, Apr 19, 2020
  26. Martin ÅgrenApr 19, 2020
  27. Danh DoanApr 19, 2020
  28. 3/3 mailinfo: disallow NUL character in mail's headerĐoàn Trần Công Danh, Apr 19, 2020
  29. Martin ÅgrenApr 19, 2020
  30. Danh DoanApr 19, 2020
  31. 2/3 mailinfo.c::convert_to_utf8: reuse strlen infoĐoàn Trần Công Danh, Apr 19, 2020
  32. Martin ÅgrenApr 19, 2020
  33. Danh DoanApr 19, 2020
  34. Junio C HamanoApr 20, 2020
  35. Danh DoanApr 20, 2020
  36. 0/3 Disallow NUL character in mailinfoĐoàn Trần Công Danh, Apr 20, 2020
  37. 1/3 t4254: merge 2 steps of a single testĐoàn Trần Công Danh, Apr 20, 2020
  38. 2/3 mailinfo.c: avoid strlen on strings that can contains NULĐoàn Trần Công Danh, Apr 20, 2020
  39. 3/3 mailinfo: disallow NUL character in mail's headerĐoàn Trần Công Danh, Apr 20, 2020

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