I would like to examine the response just before it's dispatched to the client. Primarily, I'm interested in the ;; ANSWER SECTION:
.
What had looked like a trivial modification of logDnsMsg function turned out to be a dounting task of browsing reply_info
, rrset_ref
and ub_packed_rrset_key
structures in pursuit of the desired ;; ANSWER SECTION:
bytes.
The reason is the logDnsMsg function does not work as expected for A
queries ;; ANSWER SECTION:
, while it suprisingly operates as expected for ;; AUTHORITY SECTION:
on AAAA
queries.
Lemme demonstrate a comparison between the Python implemented logDnsMsg function and a native log_dns_msg function; with the former displaying a gibberish and the latter performing exactly as expected. Both functions are called from within the Python module context as follows:
+++
def operate(id, event, qstate, qdata):
log_info("pythonmod: operate called, id: %d, event:%s" % (id, strmodulevent(event)))
if (qstate.return_msg):
logDnsMsg(qstate)
log_dns_msg("blackpie KARMMMMMM XXXXXXX", qstate.return_msg.qinfo, qstate.return_msg.rep)
+++
Note that I altered the original logDnsMsg so as it uses the logging framework in favour of print
. The output was the same for print
but for being scattered across the logfile at buffer's discretion.
dig
output:
karm@localhost:~$ dig seznam.cz @127.0.0.1 -p53535
; <<>> DiG 9.9.4-P2-RedHat-9.9.4-18.P2.fc20 <<>> seznam.cz @127.0.0.1 -p53535
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 38630
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;seznam.cz. IN A
;; ANSWER SECTION:
seznam.cz. 300 IN A 77.75.76.3
;; Query time: 656 msec
;; SERVER: 127.0.0.1#53535(127.0.0.1)
;; WHEN: Sat Apr 25 16:04:32 CEST 2015
;; MSG SIZE rcvd: 54
Output for AAAA
query, ;; AUTHORITY SECTION:
looks decent enough from both logDnsMsg and log_dns_msg:
[1429970672] unbound[14053:0] info: pythonmod: operate called, id: 1, event:module_event_moddone
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: Query: e.root-servers.net., type: AAAA (28), class: IN (1)
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: Return reply :: flags: 8080, QDcount: 1, Security:0, TTL=86400
[1429970672] unbound[14053:0] info: qinfo :: qname: ['e', 'root-servers', 'net', ''] e.root-servers.net., qtype: AAAA, qclass: IN
[1429970672] unbound[14053:0] info: Reply:
[1429970672] unbound[14053:0] info: 0:['root-servers', 'net', ''] root-servers.net. flags: 0004
[1429970672] unbound[14053:0] info: type:SOA (6) class:IN (1)
[1429970672] unbound[14053:0] info: 0:TTL=3600000
[1429970672] unbound[14053:0] info:
[1429970672] unbound[14053:0] info: 0x00 | 00 40 01 61 0C 72 6F 6F 74 2D 73 65 72 76 65 72 73 | . @ . a . r o o t - s e r v e r s
0x10 | 73 03 6E 65 74 00 05 6E 73 74 6C 64 0C 76 65 72 69 | s . n e t . . n s t l d . v e r i
0x20 | 69 73 69 67 6E 2D 67 72 73 03 63 6F 6D 00 78 0C E3 | i s i g n - g r s . c o m . x . .
0x30 | E3 24 00 00 38 40 00 00 1C 20 00 12 75 00 00 36 EE | . $ . . 8 @ . . . . . u . . 6 .
0x40 | EE 80 | . .
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: blackpie KARMMMMMM XXXXXXX ;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 0
;; flags: qr ra ; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
e.root-servers.net. IN AAAA
;; ANSWER SECTION:
;; AUTHORITY SECTION:
root-servers.net. 3600000 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2014110500 14400 7200 1209600 3600000
;; ADDITIONAL SECTION:
;; MSG SIZE rcvd: 96
[1429970672] unbound[14053:0] debug: mesh_run: python module exit state is module_finished
On the contrary, for A
query, ;; ANSWER SECTION:
is completely useless as far as logDnsMsg goes:
[1429970672] unbound[14053:0] info: pythonmod: operate called, id: 1, event:module_event_moddone
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: Query: seznam.cz., type: A (1), class: IN (1)
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: Return reply :: flags: 8080, QDcount: 1, Security:0, TTL=300
[1429970672] unbound[14053:0] info: qinfo :: qname: ['seznam', 'cz', ''] seznam.cz., qtype: A, qclass: IN
[1429970672] unbound[14053:0] info: Reply:
[1429970672] unbound[14053:0] info: 0:['seznam', 'cz', ''] seznam.cz. flags: 0000
[1429970672] unbound[14053:0] info: type:A (1) class:IN (1)
[1429970672] unbound[14053:0] info: 0:TTL=300
[1429970672] unbound[14053:0] info:
[1429970672] unbound[14053:0] info: 0x00 | 00 04 4D 4B 4C 03 | . . M K L .
[1429970672] unbound[14053:0] info: ------------------------------------------------------------------------------------------
[1429970672] unbound[14053:0] info: blackpie KARMMMMMM XXXXXXX ;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 0
;; flags: qr ra ; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
seznam.cz. IN A
;; ANSWER SECTION:
seznam.cz. 300 IN A 77.75.76.3
;; AUTHORITY SECTION:
;; ADDITIONAL SECTION:
;; MSG SIZE rcvd: 43
[1429970672] unbound[14053:0] debug: mesh_run: python module exit state is module_finished
Note the 00 04 4D 4B 4C 03
bytes that are erroneously interpreted as ASCII.
Where in the struct ub_packed_rrset_key** rrsets;
one finds the desired ;; ANSWER SECTION:
data? (If it is indeed the right place to look.)
I've been fiddling with it for quite some time without any luck. I examined the sldns_wire2str_pkt_scan
function that is used internally for unpacking the wire
binary data, but I am none the wiser.