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Name Decompression

$Id: decompression,v 1.8 2004/03/05 05:04:46 marka Exp $

Overview.

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

local 14 bit and local 16 bit.

In general the resolver / nameserver should accept any compression

method at any time regardless of whether it was legal to

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

what you accept and strict with what you send.

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

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

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

or in a question.

When performing regression testing however we should be as strict

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

decompression routines.

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

following pieces of information.

1. where the message starts.

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

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

4. where the domainname we are decompressing starts.

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

and edn version.

Implementation:

dns_rdata_fromwire will set the allowed decompression methods allowed

by looking at edns, strict and the type values.

Types:

struct dns_decompress {

unsigned int magic;

unsigned int allowed;

int edns;

dns_name_t owner_name;

unsigned int rdata;

isc_boolean_t strict;

}

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)