Peter Saint-Andre wrote:
> Justin Karneges wrote:
>> On Wednesday 05 November 2008 14:00:35 Peter Saint-Andre wrote:
>>> Discussion: Dave raised some questions about the TXT record data format.
>>> Peter to ping the DNS-SD authors, Dave and Ralph to do some testing of
>>> real-world deployments.
>> Kev fails for not contacting me about this. The dig output is pretty and
>> doesn't include the length byte which is indeed in the record data. The
>> question is really about XEP-174's usage of that "text-based DNS record
>> description notation" (for lack of a better name) in the context of
>> representing multiple strings, and not about the actual TXT raw byte format
>> of which there is no dispute.
>>
>> I'm not sure if there's an authoritative source for that text-based DNS
>> record
>> description notation (other than RFC 1035, which is quite sketchy), but
>> information about SPF reveals the use of multiple strings in one line. E.g.:
>>
>> example.com. 4500 IN TXT "string1" "string2" "string3"
>>
>> Indeed, sending dig at a TXT record containing multiple strings prints the
>> result exactly this way. You can dig iChat like this:
>>
>> dig @ip_address_of_ichat -p 5353 -t txt [EMAIL PROTECTED]
>>
>> So, I think the right answer is to put all strings on one line.
>>
>> From what I can tell, the DNS-SD spec dodges this topic by not using the
>> notation at all, which is not a bad approach either. :) It's not like
>> anyone
>> implementing XEP-174 will be parsing this format.
>
> Yes, I noticed that output in dig, too. Then I tried to watch it using
> tcpdump ('tcpdump -x -X -s 5000 -l -vvv host roundabout.local' in my case):
>
> 16:28:12.408064 IP6 (hlim 255, next-header: UDP (17), length: 331)
> roundabout.local.mdns > ff02::fb.mdns: [udp sum ok] 0*- [0q] 4/0/2
> [EMAIL PROTECTED] (Cache flush) SRV
> roundabout.local.:53589 0 0, [EMAIL PROTECTED]
> (Cache flush) TXT "txtvers=1" "port.p2pj=53589" "status=avail"
> "1st=Peter" "[EMAIL PROTECTED]" "[EMAIL PROTECTED]"
> "last=Saint-Andre" "vc=SDCURA!XN" "ext=5I",
> _services._dns-sd._udp.local. PTR _presence._tcp.local.,
> _presence._tcp.local. PTR [EMAIL PROTECTED] ar:
> roundabout.local. (Cache flush) AAAA roundabout.local, roundabout.local.
> (Cache flush) A my.domain.com (323)
>
> 0x0000: 6000 0000 014b 11ff fe80 0000 0000 0000 `....K..........
> 0x0010: 020d 93ff fe2c 5c18 ff02 0000 0000 0000 .....,\.........
> 0x0020: 0000 0000 0000 00fb 14e9 14e9 014b eba5 .............K..
> 0x0030: 0000 8400 0000 0004 0000 0002 1273 7470 .............stp
> 0x0040: 6574 6572 4072 6f75 6e64 6162 6f75 7409 [EMAIL PROTECTED]
> 0x0050: 5f70 7265 7365 6e63 6504 5f74 6370 056c _presence._tcp.l
> 0x0060: 6f63 616c 0000 2180 0100 0000 7800 1300 ocal..!.....x...
> 0x0070: 0000 00d1 550a 726f 756e 6461 626f 7574 ....U.roundabout
> 0x0080: c02e c00c 0010 8001 0000 1194 0086 0974 ...............t
> 0x0090: 7874 7665 7273 3d31 0f70 6f72 742e 7032 xtvers=1.port.p2
> 0x00a0: 706a 3d35 3335 3839 0c73 7461 7475 733d pj=53589.status=
> 0x00b0: 6176 6169 6c09 3173 743d 5065 7465 7218 avail.1st=Peter.
> 0x00c0: 656d 6169 6c3d 7374 7065 7465 7240 7374 [EMAIL PROTECTED]
> 0x00d0: 7065 7465 722e 696d 166a 6964 3d73 7470 peter.im.jid=stp
> 0x00e0: 6574 6572 4073 7470 6574 6572 2e69 6d10 [EMAIL PROTECTED]
> 0x00f0: 6c61 7374 3d53 6169 6e74 2d41 6e64 7265 last=Saint-Andre
> 0x0100: 0c76 633d 5344 4355 5241 2158 4e06 6578 .vc=SDCURA!XN.ex
> 0x0110: 743d 3549 095f 7365 7276 6963 6573 075f t=5I._services._
> 0x0120: 646e 732d 7364 045f 7564 70c0 2e00 0c00 dns-sd._udp.....
> 0x0130: 0100 0011 9400 02c0 1fc0 1f00 0c00 0100 ................
> 0x0140: 0011 9400 02c0 0cc0 4500 1c80 0100 0000 ........E.......
> 0x0150: 7800 10fe 8000 0000 0000 0002 0d93 fffe x...............
> 0x0160: 2c5c 18c0 4500 0180 0100 0000 7800 040a ,\..E.......x...
> 0x0170: 0201 e1
>
> I'm not sure what to conclude from that...
Never mind. It does seem that the single byte length indicators are
included on the wire. So for instance the key-value pair txtvers=1 is
preceded by hex 09 (length 9), the pair status=avail is preceded by hex
0c (length 12), the pair [EMAIL PROTECTED] is preceded by hex 18
(length 24), and so on.
/psa
