Initial design document

doc/design/decompression

+		
+		Name Decompression
+
+	$Id: decompression,v 1.1 1999/02/24 00:51:13 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.
+
+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:
+
+	dns_result_t
+	dns_decompress_init(dns_decompress_t *dctx, int edns,
+			    isc_boolean_t strict, isc_mctx_t *mctx);
+	initalise dctx
+	dctx->ownername is invalidated
+
+	dns_result_t
+	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)