[vorbis-dev] small bug

[Erik Kruus]

The comments strings in vorbis are to be 8-bit clean.

info.c _v_writestring is not 8-bit clean.  This leads to a malformed
comment header packet if the comment has an embedded Null:

   0:0  hdr2 03 76 6F 72 62 69 73 20  00 00 00 58 69 70 68 6F .vorbis  ...Xipho
  16:10      70 68 6F 72 75 73 20 6C  69 62 56 6F 72 62 69 73 phorus l ibVorbis
  32:20      20 49 20 32 30 30 31 30  38 31 33 01 00 00 00 65  I 20010 813....e
                                                           ^^length (true)
  48:30      00 00 00 54 72 61 63 6B  20 65 6E 63 6F 64 65 64 ...Track  encoded
  64:40      20 62 79 20 65 6E 63 6F  64 65 72 5F 65 78 61 6D  by enco der_exam
  80:50      70 6C 65 2E 63 0D 0A 09  09 57 69 74 68 20 61 20 ple.c... .With a 
  96:60      6E 75 6C 6C 2D 62 65 65  70 20 68 65 72 65 2D 2D null-bee p here--
 112:70      3E 3C 01                                         ><.            
                  ..."\0\007>\r\n\t\t and a null-beep there<\0\007>\r\n"...

                vorbis has cut off my astounding poetry.   The nerve!

                It's also spitting out a malformed header, which is clearly
                of secondary import here.

as you see, the actually length written is only around 0x40.,
So any subsequent headers would be unfindable when reading.
And reading might cause a sort of crashing behaviour for some folks.

The fix is trivial: use a version of _v_writestring for the 8-bit
clean input that accepts a byte-count argument. (around line 44 of info.c)
and supply the byte-count argument in _vorbis_pack_comment (around line 428)
(The vendor string uses strlen, so cannot possibly have an embedded NUL
 it seems, so that bit is fine)

Note the _v_readstring (correctly, for comment headers w/ embedded NULs)
has a byte-count, and should work just fine when unpacking correctly-formed
headers (but would would bomb or give garbled poetry as it reads past the
short end-of-packet).

Of course, to add 8-bit clean data, one has to muck with vc.user_comments
directly, since no easy way to add an 8-bit-clean comment is provided
by the current API.

Anyway, either the spec or the code has to change.  I hope it's the code,
so I can make my totally unworthy t-shirt claim.  And yah, I realize the
comment tools don't handle the spec'ed 8-bit cleanliness yet either.

Erik.

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