[PATCH 3/6] daemon: fix off-by-one in logging extended attributes

If receive a request like:

  git-upload-pack /foo.git\0host=localhost

we mark the offset of the NUL byte as "len", and then log the bytes after the NUL with a "%.*s" placeholder, using "pktlen - len" as the length, and "line + len + 1" as the start of the string.

This is off-by-one, since the start of the string skips past the separating NUL byte, but the adjusted length includes it. Fortunately this doesn't actually read past the end of the buffer, since "%.*s" will stop when it hits a NUL. And regardless of what is in the buffer, packet_read() will always add an extra NUL terminator for safety.

As an aside, the git.git client sends an extra NUL after a "host" field, too, so we'd generally hit that one first, not the one added by packet_read(). You can see this in the test output which reports 15 bytes, even though the string has only 14 bytes of visible data. But the point is that even a client sending unusual data could not get us to read past the end of the buffer, so this is purely a cosmetic fix.

Reported-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>
---
This code actually goes away in the next patch, but I thought it was
worth dealing with individually, since it is a memory error (albeit a
harmless one).

 daemon.c              |  4 ++--
 t/t5570-git-daemon.sh | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)