da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chinCopyright (C) 1999, 2000 Internet Software Consortium.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chinSee COPYRIGHT in the source root or http://www.isc.org/copyright for terms.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

3e14f97f673e8a630f076077de35afdd43dc1587Roger A. Faulkner Name Decompression

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin $Id: decompression,v 1.4 2000/06/21 23:43:32 tale Exp $

7c2fbfb345896881c631598ee3852ce9ce33fb07April Chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chinOverview.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin There are 4 type of compression: global 14 bit, global 16 bit,

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin local 14 bit and local 16 bit.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin In general the resolver / nameserver should accept any compression

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin method at any time regardless of whether it was legal to

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin send it. This fits with the priciple of being liberal with

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin what you accept and strict with what you send.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin There are a few cases where it does not make sence to accept

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin compression pointers of a given type. i.e. the first domain name

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin in a message, local compression pointers in the ownername of a RR

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin or in a question.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin When performing regression testing however we should be as strict

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin as possible. Hence we need to be able modifiy the behaviour of the

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin decompression routines.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin To be able to decompress a domain name we need some or all of the

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin following pieces of information.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin 1. where the message starts.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin 2. where the current rdata starts in the message (local compression).

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin 3. what the current owner name is (local compression).

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin 4. where the domainname we are decompressing starts.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin 5. what are allowable decompression method. These vary across type

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin and edn version.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chinImplementation:

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin dns_rdata_fromwire will set the allowed decompression methods allowed

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin by looking at edns, strict and the type values.

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chinTypes:

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin struct dns_decompress {

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin unsigned int magic;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin unsigned int allowed;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin int edns;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin dns_name_t owner_name;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin unsigned int rdata;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin isc_boolean_t strict;

da2e3ebdc1edfbc5028edf1354e7dd2fa69a7968chin }

Functions:

void

dns_decompress_init(dns_decompress_t *dctx, int edns,

isc_boolean_t strict);

initalise dctx

dctx->ownername is invalidated

void

dns_decompress_localinit(dns_decompress_t *dctx, dns_name_t *name,

isc_buffer_t *source);

initalise dctx->ownername

record source->current to dctx->rdata

void

dns_decompress_invalidate(dns_decompress_t *dctx);

invalidate dctx

void

dns_decompress_localinvalidate(dns_decompress_t *dctx);

invalidate dctx->ownername

void

dns_decompress_setmethods(dns_decompress_t *dctx, unsigned int allowed);

sets dctx->allowed

unsigned int

dns_decompress_getmethods(dns_decompress_t *dctx);

returns dctx->allowed

int

dns_decompress_edns(dns_decompress_t *dctx);

returns dctx->edns

isc_boolean_t

dns_decompress_strict(dns_decompress_t *dctx);

returns dctx->strict

dns_result_t

dns_name_fromwire(dns_name_t *name, isc_buffer_t *source,

dns_decompress_t *dctx, isc_boolean_t downcase,

isc_buffer_t *target)