message.c

/*
 * Copyright (C) 1999  Internet Software Consortium.
 * 
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/***
 *** Imports
 ***/

#include <config.h>

#include <stddef.h>
#include <string.h>

#include <isc/assertions.h>
#include <isc/boolean.h>
#include <isc/region.h>
#include <isc/types.h>

#include <dns/message.h>
#include <dns/rdataset.h>
#include <dns/rdata.h>
#include <dns/rdataclass.h>
#include <dns/rdatatype.h>
#include <dns/rdatalist.h>
#include <dns/compress.h>
#include <dns/tsig.h>

#define DNS_MESSAGE_OPCODE_MASK		0x7800U
#define DNS_MESSAGE_OPCODE_SHIFT	    11
#define DNS_MESSAGE_RCODE_MASK		0x000fU
#define DNS_MESSAGE_FLAG_MASK		0x8ff0U

#define VALID_NAMED_SECTION(s)  (((s) > DNS_SECTION_ANY) \
				 && ((s) < DNS_SECTION_MAX))
#define VALID_SECTION(s)	(((s) >= DNS_SECTION_ANY) \
				 && ((s) < DNS_SECTION_MAX))

/*
 * This is the size of each individual scratchpad buffer, and the numbers
 * of various block allocations used within the server.
 * XXXMLG These should come from a config setting.
 */
#define SCRATCHPAD_SIZE		512
#define NAME_COUNT		  8
#define RDATA_COUNT		  8
#define RDATALIST_COUNT		  8
#define RDATASET_COUNT		 RDATALIST_COUNT

/*
 * "helper" type, which consists of a block of some type, and is linkable.
 * For it to work, sizeof(dns_msgblock_t) must be a multiple of the pointer
 * size, or the allocated elements will not be alligned correctly.
 */
struct dns_msgblock {
	unsigned int			count;
	unsigned int			remaining;
	ISC_LINK(dns_msgblock_t)	link;
}; /* dynamically sized */

static inline dns_msgblock_t *
msgblock_allocate(isc_mem_t *, unsigned int, unsigned int);

#define msgblock_get(block, type) \
	((type *)msgblock_internalget(block, sizeof(type)))

static inline void *
msgblock_internalget(dns_msgblock_t *, unsigned int);

static inline void
msgblock_reset(dns_msgblock_t *);

static inline void
msgblock_free(isc_mem_t *, dns_msgblock_t *, unsigned int);

/*
 * Allocate a new dns_msgblock_t, and return a pointer to it.  If no memory
 * is free, return NULL.
 */
static inline dns_msgblock_t *
msgblock_allocate(isc_mem_t *mctx, unsigned int sizeof_type,
		  unsigned int count)
{
	dns_msgblock_t *block;
	unsigned int length;

	length = sizeof(dns_msgblock_t) + (sizeof_type * count);

	block = isc_mem_get(mctx, length);
	if (block == NULL)
		return (NULL);

	block->count = count;
	block->remaining = count;

	ISC_LINK_INIT(block, link);

	return (block);
}

/*
 * Return an element from the msgblock.  If no more are available, return
 * NULL.
 */
static inline void *
msgblock_internalget(dns_msgblock_t *block, unsigned int sizeof_type)
{
	void *ptr;

	if (block == NULL || block->remaining == 0)
		return (NULL);

	block->remaining--;

	ptr = (((unsigned char *)block)
	       + sizeof(dns_msgblock_t)
	       + (sizeof_type * block->remaining));

	return (ptr);
}

static inline void
msgblock_reset(dns_msgblock_t *block)
{
	block->remaining = block->count;
}

/*
 * Release memory associated with a message block.
 */
static inline void
msgblock_free(isc_mem_t *mctx, dns_msgblock_t *block,
	      unsigned int sizeof_type)
{
	unsigned int length;

	length = sizeof(dns_msgblock_t) + (sizeof_type * block->count);

	isc_mem_put(mctx, block, length);
}

/*
 * Allocate a new dynamic buffer, and attach it to this message as the
 * "current" buffer.  (which is always the last on the list, for our
 * uses)
 */
static inline dns_result_t
newbuffer(dns_message_t *msg, unsigned int size)
{
	isc_result_t result;
	isc_dynbuffer_t *dynbuf;

	dynbuf = NULL;
	result = isc_dynbuffer_allocate(msg->mctx, &dynbuf, size,
					ISC_BUFFERTYPE_BINARY);
	if (result != ISC_R_SUCCESS)
		return (DNS_R_NOMEMORY);

	ISC_LIST_APPEND(msg->scratchpad, dynbuf, link);
	return (DNS_R_SUCCESS);
}

static inline isc_buffer_t *
currentbuffer(dns_message_t *msg)
{
	isc_dynbuffer_t *dynbuf;

	dynbuf = ISC_LIST_TAIL(msg->scratchpad);
	INSIST(dynbuf != NULL);

	return (&dynbuf->buffer);
}

static inline void
releasename(dns_message_t *msg, dns_name_t *name)
{
	ISC_LIST_PREPEND(msg->freename, name, link);
}

static inline dns_name_t *
newname(dns_message_t *msg)
{
	dns_msgblock_t *msgblock;
	dns_name_t *name;

	name = ISC_LIST_HEAD(msg->freename);
	if (name != NULL) {
		ISC_LIST_UNLINK(msg->freename, name, link);
		return (name);
	}

	msgblock = ISC_LIST_TAIL(msg->names);
	name = msgblock_get(msgblock, dns_name_t);
	if (name == NULL) {
		msgblock = msgblock_allocate(msg->mctx, sizeof(dns_name_t),
					     NAME_COUNT);
		if (msgblock == NULL)
			return (NULL);

		ISC_LIST_APPEND(msg->names, msgblock, link);

		name = msgblock_get(msgblock, dns_name_t);
	}

	return (name);
}

static inline void
releaserdata(dns_message_t *msg, dns_rdata_t *rdata)
{
	ISC_LIST_PREPEND(msg->freerdata, rdata, link);
}

static inline dns_rdata_t *
newrdata(dns_message_t *msg)
{
	dns_msgblock_t *msgblock;
	dns_rdata_t *rdata;

	rdata = ISC_LIST_HEAD(msg->freerdata);
	if (rdata != NULL) {
		ISC_LIST_UNLINK(msg->freerdata, rdata, link);
		return (rdata);
	}

	msgblock = ISC_LIST_TAIL(msg->rdatas);
	rdata = msgblock_get(msgblock, dns_rdata_t);
	if (rdata == NULL) {
		msgblock = msgblock_allocate(msg->mctx, sizeof(dns_rdata_t),
					     RDATA_COUNT);
		if (msgblock == NULL)
			return (NULL);

		ISC_LIST_APPEND(msg->rdatas, msgblock, link);

		rdata = msgblock_get(msgblock, dns_rdata_t);
	}

	return (rdata);
}

static inline void
releaserdatalist(dns_message_t *msg, dns_rdatalist_t *rdatalist)
{
	ISC_LIST_PREPEND(msg->freerdatalist, rdatalist, link);
}

static inline dns_rdatalist_t *
newrdatalist(dns_message_t *msg)
{
	dns_msgblock_t *msgblock;
	dns_rdatalist_t *rdatalist;

	rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
	if (rdatalist != NULL) {
		ISC_LIST_UNLINK(msg->freerdatalist, rdatalist, link);
		return (rdatalist);
	}

	msgblock = ISC_LIST_TAIL(msg->rdatalists);
	rdatalist = msgblock_get(msgblock, dns_rdatalist_t);
	if (rdatalist == NULL) {
		msgblock = msgblock_allocate(msg->mctx,
					     sizeof(dns_rdatalist_t),
					     RDATALIST_COUNT);
		if (msgblock == NULL)
			return (NULL);

		ISC_LIST_APPEND(msg->rdatalists, msgblock, link);

		rdatalist = msgblock_get(msgblock, dns_rdatalist_t);
	}

	return (rdatalist);
}

static inline void
releaserdataset(dns_message_t *msg, dns_rdataset_t *rdataset)
{
	ISC_LIST_PREPEND(msg->freerdataset, rdataset, link);
}

static inline dns_rdataset_t *
newrdataset(dns_message_t *msg)
{
	dns_msgblock_t *msgblock;
	dns_rdataset_t *rdataset;

	rdataset = ISC_LIST_HEAD(msg->freerdataset);
	if (rdataset != NULL) {
		ISC_LIST_UNLINK(msg->freerdataset, rdataset, link);
		return (rdataset);
	}

	msgblock = ISC_LIST_TAIL(msg->rdatasets);
	rdataset = msgblock_get(msgblock, dns_rdataset_t);
	if (rdataset == NULL) {
		msgblock = msgblock_allocate(msg->mctx, sizeof(dns_rdataset_t),
					     RDATASET_COUNT);
		if (msgblock == NULL)
			return (NULL);

		ISC_LIST_APPEND(msg->rdatasets, msgblock, link);

		rdataset = msgblock_get(msgblock, dns_rdataset_t);
	}

	return (rdataset);
}

static inline void
msginitheader(dns_message_t *m)
{
	m->id = 0;
	m->flags = 0;
	m->rcode = 0;
	m->opcode = 0;
	m->rdclass = 0;
}

static inline void
msginitprivate(dns_message_t *m)
{
	unsigned int i;

	for (i = 0; i < DNS_SECTION_MAX; i++) {
		m->cursors[i] = NULL;
		m->counts[i] = 0;
	}
	m->opt = NULL;
	m->state = DNS_SECTION_ANY;  /* indicate nothing parsed or rendered */
	m->reserved = 0;
	m->buffer = NULL;
	m->need_cctx_cleanup = 0;
}

static inline void
msginittsig(dns_message_t *m)
{
	m->tsigstatus = m->querytsigstatus = dns_rcode_noerror;
	m->tsig = m->querytsig = NULL;
	m->tsigkey = NULL;
	m->tsigstart = -1;
}

/*
 * Init elements to default state.  Used both when allocating a new element
 * and when resetting one.
 */
static inline void
msginit(dns_message_t *m)
{
	msginitheader(m);
	msginitprivate(m);
	msginittsig(m);
	m->header_ok = 0;
	m->question_ok = 0;
}

static inline void
msgresetnames(dns_message_t *msg, unsigned int first_section) {
	unsigned int i;
	dns_name_t *name, *next_name;
	dns_rdataset_t *rds, *next_rds;

	/*
	 * Clean up name lists by calling the rdataset disassociate function.
	 */
	for (i = first_section; i < DNS_SECTION_MAX; i++) {
		name = ISC_LIST_HEAD(msg->sections[i]);
		while (name != NULL) {
			next_name = ISC_LIST_NEXT(name, link);
			ISC_LIST_UNLINK(msg->sections[i], name, link);

			rds = ISC_LIST_HEAD(name->list);
			while (rds != NULL) {
				next_rds = ISC_LIST_NEXT(rds, link);
				ISC_LIST_UNLINK(name->list, rds, link);

				dns_rdataset_disassociate(rds);
				rds = next_rds;
			}
			name = next_name;
		}
	}
}

/*
 * Free all but one (or everything) for this message.  This is used by
 * both dns_message_reset() and dns_message_parse().
 */
static void
msgreset(dns_message_t *msg, isc_boolean_t everything)
{
	dns_msgblock_t *msgblock, *next_msgblock;
	isc_dynbuffer_t *dynbuf, *next_dynbuf;
	dns_rdataset_t *rds;
	dns_name_t *name;
	dns_rdata_t *rdata;
	dns_rdatalist_t *rdatalist;

	msgresetnames(msg, 0);

	/*
	 * Clean up linked lists.
	 */

	/*
	 * Run through the free lists, and just unlink anything found there.
	 * The memory isn't lost since these are part of message blocks we
	 * have allocated.
	 */
	name = ISC_LIST_HEAD(msg->freename);
	while (name != NULL) {
		ISC_LIST_UNLINK(msg->freename, name, link);
		name = ISC_LIST_HEAD(msg->freename);
	}
	rdata = ISC_LIST_HEAD(msg->freerdata);
	while (rdata != NULL) {
		ISC_LIST_UNLINK(msg->freerdata, rdata, link);
		rdata = ISC_LIST_HEAD(msg->freerdata);
	}
	rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
	while (rdatalist != NULL) {
		ISC_LIST_UNLINK(msg->freerdatalist, rdatalist, link);
		rdatalist = ISC_LIST_HEAD(msg->freerdatalist);
	}
	rds = ISC_LIST_HEAD(msg->freerdataset);
	while (rds != NULL) {
		ISC_LIST_UNLINK(msg->freerdataset, rds, link);
		rds = ISC_LIST_HEAD(msg->freerdataset);
	}

	dynbuf = ISC_LIST_HEAD(msg->scratchpad);
	INSIST(dynbuf != NULL);
	if (!everything) {
		isc_dynbuffer_reset(dynbuf);
		dynbuf = ISC_LIST_NEXT(dynbuf, link);
	}
	while (dynbuf != NULL) {
		next_dynbuf = ISC_LIST_NEXT(dynbuf, link);
		ISC_LIST_UNLINK(msg->scratchpad, dynbuf, link);
		isc_dynbuffer_free(msg->mctx, &dynbuf);
		dynbuf = next_dynbuf;
	}

	msgblock = ISC_LIST_HEAD(msg->names);
	INSIST(msgblock != NULL);
	if (!everything) {
		msgblock_reset(msgblock);
		msgblock = ISC_LIST_NEXT(msgblock, link);
	}
	while (msgblock != NULL) {
		next_msgblock = ISC_LIST_NEXT(msgblock, link);
		ISC_LIST_UNLINK(msg->names, msgblock, link);
		msgblock_free(msg->mctx, msgblock, sizeof(dns_name_t));
		msgblock = next_msgblock;
	}

	msgblock = ISC_LIST_HEAD(msg->rdatas);
	INSIST(msgblock != NULL);
	if (!everything) {
		msgblock_reset(msgblock);
		msgblock = ISC_LIST_NEXT(msgblock, link);
	}
	while (msgblock != NULL) {
		next_msgblock = ISC_LIST_NEXT(msgblock, link);
		ISC_LIST_UNLINK(msg->rdatas, msgblock, link);
		msgblock_free(msg->mctx, msgblock, sizeof(dns_rdata_t));
		msgblock = next_msgblock;
	}

	msgblock = ISC_LIST_HEAD(msg->rdatasets);
	INSIST(msgblock != NULL);
	if (!everything) {
		msgblock_reset(msgblock);
		msgblock = ISC_LIST_NEXT(msgblock, link);
	}
	while (msgblock != NULL) {
		next_msgblock = ISC_LIST_NEXT(msgblock, link);
		ISC_LIST_UNLINK(msg->rdatasets, msgblock, link);
		msgblock_free(msg->mctx, msgblock, sizeof(dns_rdataset_t));
		msgblock = next_msgblock;
	}

	/*
	 * rdatalists could be empty.
	 */

	msgblock = ISC_LIST_HEAD(msg->rdatalists);
	if (!everything && msgblock != NULL) {
		msgblock_reset(msgblock);
		msgblock = ISC_LIST_NEXT(msgblock, link);
	}
	while (msgblock != NULL) {
		next_msgblock = ISC_LIST_NEXT(msgblock, link);
		ISC_LIST_UNLINK(msg->rdatalists, msgblock, link);
		msgblock_free(msg->mctx, msgblock, sizeof(dns_rdatalist_t));
		msgblock = next_msgblock;
	}

	if (msg->need_cctx_cleanup == 1)
		dns_compress_invalidate(&msg->cctx);

	if (msg->tsig != NULL) {
		dns_rdata_freestruct(msg->tsig);
		isc_mem_put(msg->mctx, msg->tsig, sizeof(dns_rdata_any_tsig_t));
	}

	if (msg->querytsig != NULL) {
		dns_rdata_freestruct(msg->querytsig);
		isc_mem_put(msg->mctx, msg->querytsig,
			    sizeof(dns_rdata_any_tsig_t));
        }

	if (msg->tsigkey != NULL && dns_tsig_emptykey(msg->tsigkey))
		dns_tsig_key_free(&msg->tsigkey);

	/*
	 * Set other bits to normal default values.
	 */
	if (!everything)
		msginit(msg);
}

dns_result_t
dns_message_create(isc_mem_t *mctx, unsigned int intent, dns_message_t **msgp)
{
	dns_message_t *m;
	isc_result_t iresult;
	dns_msgblock_t *msgblock;
	isc_dynbuffer_t *dynbuf;
	unsigned int i;

	REQUIRE(mctx != NULL);
	REQUIRE(msgp != NULL);
	REQUIRE(*msgp == NULL);
	REQUIRE(intent == DNS_MESSAGE_INTENTPARSE
		|| intent == DNS_MESSAGE_INTENTRENDER);

	m = isc_mem_get(mctx, sizeof(dns_message_t));
	if (m == NULL)
		return(DNS_R_NOMEMORY);

	m->magic = DNS_MESSAGE_MAGIC;
	m->from_to_wire = intent;
	msginit(m);
	for (i = 0 ; i < DNS_SECTION_MAX ; i++)
		ISC_LIST_INIT(m->sections[i]);
	m->mctx = mctx;
	ISC_LIST_INIT(m->scratchpad);
	ISC_LIST_INIT(m->names);
	ISC_LIST_INIT(m->rdatas);
	ISC_LIST_INIT(m->rdatasets);
	ISC_LIST_INIT(m->rdatalists);
	ISC_LIST_INIT(m->freename);
	ISC_LIST_INIT(m->freerdata);
	ISC_LIST_INIT(m->freerdataset);
	ISC_LIST_INIT(m->freerdatalist);

	dynbuf = NULL;
	iresult = isc_dynbuffer_allocate(mctx, &dynbuf, SCRATCHPAD_SIZE,
					 ISC_BUFFERTYPE_BINARY);
	if (iresult != ISC_R_SUCCESS)
		goto cleanup1;
	ISC_LIST_APPEND(m->scratchpad, dynbuf, link);

	msgblock = msgblock_allocate(mctx, sizeof(dns_name_t),
				     NAME_COUNT);
	if (msgblock == NULL)
		goto cleanup2;
	ISC_LIST_APPEND(m->names, msgblock, link);

	msgblock = msgblock_allocate(mctx, sizeof(dns_rdata_t),
				     RDATA_COUNT);
	if (msgblock == NULL)
		goto cleanup3;
	ISC_LIST_APPEND(m->rdatas, msgblock, link);

	msgblock = msgblock_allocate(mctx, sizeof(dns_rdataset_t),
				     RDATASET_COUNT);
	if (msgblock == NULL)
		goto cleanup4;
	ISC_LIST_APPEND(m->rdatasets, msgblock, link);

	if (intent == DNS_MESSAGE_INTENTPARSE) {
		msgblock = msgblock_allocate(mctx, sizeof(dns_rdatalist_t),
					     RDATALIST_COUNT);
		if (msgblock == NULL)
			goto cleanup5;
		ISC_LIST_APPEND(m->rdatalists, msgblock, link);
	}

	*msgp = m;
	return (DNS_R_SUCCESS);

	/*
	 * Cleanup for error returns.
	 */
 cleanup5:
	msgblock = ISC_LIST_HEAD(m->rdatasets);
	msgblock_free(mctx, msgblock, sizeof(dns_rdataset_t));
 cleanup4:
	msgblock = ISC_LIST_HEAD(m->rdatas);
	msgblock_free(mctx, msgblock, sizeof(dns_rdata_t));
 cleanup3:
	msgblock = ISC_LIST_HEAD(m->names);
	msgblock_free(mctx, msgblock, sizeof(dns_name_t));
 cleanup2:
	dynbuf = ISC_LIST_HEAD(m->scratchpad);
	isc_dynbuffer_free(mctx, &dynbuf);
 cleanup1:
	m->magic = 0;
	isc_mem_put(mctx, m, sizeof(dns_message_t));

	return (DNS_R_NOMEMORY);
}

void
dns_message_reset(dns_message_t *msg, unsigned int intent)
{
	REQUIRE(DNS_MESSAGE_VALID(msg));
	REQUIRE(intent == DNS_MESSAGE_INTENTPARSE
		|| intent == DNS_MESSAGE_INTENTRENDER);

	msg->from_to_wire = intent;
	msgreset(msg, ISC_FALSE);
}

void
dns_message_destroy(dns_message_t **msgp)
{
	dns_message_t *msg;

	REQUIRE(msgp != NULL);
	REQUIRE(DNS_MESSAGE_VALID(*msgp));

	msg = *msgp;
	*msgp = NULL;

	msgreset(msg, ISC_TRUE);
	msg->magic = 0;
	isc_mem_put(msg->mctx, msg, sizeof(dns_message_t));
}

static dns_result_t
findname(dns_name_t **foundname, dns_name_t *target, dns_namelist_t *section)
{
	dns_name_t *curr;

	for (curr = ISC_LIST_TAIL(*section) ;
	     curr != NULL ;
	     curr = ISC_LIST_PREV(curr, link)) {
		if (dns_name_equal(curr, target)) {
			if (foundname != NULL)
				*foundname = curr;
			return (DNS_R_SUCCESS);
		}
	}

	return (DNS_R_NOTFOUND);
}

static dns_result_t
findtype(dns_rdataset_t **rdataset, dns_name_t *name, dns_rdatatype_t type)
{
	dns_rdataset_t *curr;

	for (curr = ISC_LIST_TAIL(name->list) ;
	     curr != NULL ;
	     curr = ISC_LIST_PREV(curr, link)) {
		if (curr->type == type) {
			if (rdataset != NULL)
				*rdataset = curr;
			return (DNS_R_SUCCESS);
		}
	}

	return (DNS_R_NOTFOUND);
}

/*
 * Read a name from buffer "source".
 */
static dns_result_t
getname(dns_name_t *name, isc_buffer_t *source, dns_message_t *msg,
	dns_decompress_t *dctx)
{
	isc_buffer_t *scratch;
	dns_result_t result;
	unsigned int tries;

	scratch = currentbuffer(msg);

	/*
	 * First try:  use current buffer.
	 * Second try:  allocate a new buffer and use that.
	 */
	tries = 0;
	while (tries < 2) {
		dns_name_init(name, NULL);
		result = dns_name_fromwire(name, source, dctx, ISC_FALSE,
					   scratch);

		if (result == DNS_R_NOSPACE) {
			tries++;

			result = newbuffer(msg, SCRATCHPAD_SIZE);
			if (result != DNS_R_SUCCESS)
				return (result);

			scratch = currentbuffer(msg);
		} else {
			return (result);
		}
	}

	INSIST(0);  /* Cannot get here... */
	return (DNS_R_UNEXPECTED);
}

static dns_result_t
getrdata(dns_name_t *name, isc_buffer_t *source, dns_message_t *msg,
	 dns_decompress_t *dctx, dns_rdataclass_t rdclass,
	 dns_rdatatype_t rdtype, unsigned int rdatalen, dns_rdata_t *rdata)
{
	isc_buffer_t *scratch;
	dns_result_t result;
	unsigned int tries;
	unsigned int trysize;

	/*
	 * In dynamic update messages, the rdata can be empty.
	 */
	if (msg->opcode == dns_opcode_update && rdatalen == 0) {
		/*
		 * When the rdata is empty, the data pointer is never
		 * dereferenced, but it must still be non-NULL.
		 */
		rdata->data = (unsigned char *)""; 
		rdata->length = 0;
		rdata->rdclass = rdclass;
		rdata->type = rdtype;
		return DNS_R_SUCCESS;
	}
	    
	scratch = currentbuffer(msg);

	isc_buffer_setactive(source, rdatalen);
	dns_decompress_localinit(dctx, name, source);

	/*
	 * First try:  use current buffer.
	 * Second try:  allocate a new buffer of size
	 *     max(SCRATCHPAD_SIZE, 2 * compressed_rdatalen)
	 *     (the data will fit if it was not more than 50% compressed)
	 * Subsequent tries: double buffer size on each try.
	 */
	tries = 0;
	trysize = 0;
	for (;;) {
		result = dns_rdata_fromwire(rdata, rdclass, rdtype,
					    source, dctx, ISC_FALSE,
					    scratch);

		if (result == DNS_R_NOSPACE) {
			if (tries == 0) {
				trysize = 2 * rdatalen;
				if (trysize < SCRATCHPAD_SIZE)
					trysize = SCRATCHPAD_SIZE;
			} else {
				INSIST(trysize != 0);
				if (trysize >= 65535)
					return (ISC_R_NOSPACE);
					/* XXX DNS_R_RRTOOLONG? */
				trysize *= 2;
			}
			tries++;
			result = newbuffer(msg, trysize);
			if (result != DNS_R_SUCCESS)
				return (result);

			scratch = currentbuffer(msg);
		} else {
			return (result);
		}
	}
}

static dns_result_t
getquestions(isc_buffer_t *source, dns_message_t *msg, dns_decompress_t *dctx)
{
	isc_region_t r;
	unsigned int count;
	dns_name_t *name;
	dns_name_t *name2;
	dns_rdataset_t *rdataset;
	dns_rdatalist_t *rdatalist;
	dns_result_t result;
	dns_rdatatype_t rdtype;
	dns_rdataclass_t rdclass;
	dns_namelist_t *section;

	section = &msg->sections[DNS_SECTION_QUESTION];

	for (count = 0 ; count < msg->counts[DNS_SECTION_QUESTION] ; count++) {
		name = newname(msg);
		if (name == NULL)
			return (DNS_R_NOMEMORY);

		/*
		 * Parse the name out of this packet.
		 */
		isc_buffer_remaining(source, &r);
		isc_buffer_setactive(source, r.length);
		result = getname(name, source, msg, dctx);
		if (result != DNS_R_SUCCESS)
			return (result);

		/*
		 * Run through the section, looking to see if this name
		 * is already there.  If it is found, put back the allocated
		 * name since we no longer need it, and set our name pointer
		 * to point to the name we found.
		 */
		result = findname(&name2, name, section);

		/*
		 * If it is the first name in the section, accept it.
		 *
		 * If it is not, but is not the same as the name already
		 * in the question section, append to the section.  Note that
		 * here in the question section this is illegal, so return
		 * FORMERR.  In the future, check the opcode to see if
		 * this should be legal or not.  In either case we no longer
		 * need this name pointer.
		 */
		if (result != DNS_R_SUCCESS) {
			if (ISC_LIST_EMPTY(*section)) {
				ISC_LIST_APPEND(*section, name, link);
			} else {
				return (DNS_R_FORMERR);
			}
		} else {
			name = name2;
		}

		/*
		 * Get type and class.
		 */
		isc_buffer_remaining(source, &r);
		if (r.length < 4)
			return (DNS_R_UNEXPECTEDEND);
		rdtype = isc_buffer_getuint16(source);
		rdclass = isc_buffer_getuint16(source);

		/*
		 * If this class is different than the one we already read,
		 * this is an error.
		 */
		if (msg->state == DNS_SECTION_ANY) {
			msg->state = DNS_SECTION_QUESTION;
			msg->rdclass = rdclass;
			msg->state = DNS_SECTION_QUESTION;
		} else if (msg->rdclass != rdclass)
			return (DNS_R_FORMERR);
		
		/*
		 * Can't ask the same question twice.
		 */
		result = findtype(NULL, name, rdtype);
		if (result == DNS_R_SUCCESS)
			return (DNS_R_FORMERR);

		/*
		 * Allocate a new rdatalist.
		 */
		rdatalist = newrdatalist(msg);
		if (rdatalist == NULL)
			return (DNS_R_NOMEMORY);
		rdataset = newrdataset(msg);
		if (rdataset == NULL)
			return (DNS_R_NOMEMORY);

		/*
		 * Convert rdatalist to rdataset, and attach the latter to
		 * the name.
		 */
		rdatalist->type = rdtype;
		rdatalist->rdclass = rdclass;
		rdatalist->ttl = 0;
		ISC_LIST_INIT(rdatalist->rdata);

		dns_rdataset_init(rdataset);
		result = dns_rdatalist_tordataset(rdatalist, rdataset);
		if (result != DNS_R_SUCCESS)
			return (result);
		rdataset->attributes |= DNS_RDATASETATTR_QUESTION;

		ISC_LIST_APPEND(name->list, rdataset, link);
	}
	
	return (DNS_R_SUCCESS);
}

static dns_result_t
getsection(isc_buffer_t *source, dns_message_t *msg, dns_decompress_t *dctx,
	   dns_section_t sectionid, isc_boolean_t preserve_order)
{
	isc_region_t r;
	unsigned int count;
	unsigned int rdatalen;
	dns_name_t *name;
	dns_name_t *name2;
	dns_rdataset_t *rdataset;
	dns_rdatalist_t *rdatalist;
	dns_result_t result;
	dns_rdatatype_t rdtype;
	dns_rdataclass_t rdclass;
	dns_rdata_t *rdata;
	dns_ttl_t ttl;
	dns_namelist_t *section;

	for (count = 0 ; count < msg->counts[sectionid] ; count++) {
		int recstart = source->current;
		section = &msg->sections[sectionid];

		name = newname(msg);
		if (name == NULL)
			return (DNS_R_NOMEMORY);

		/*
		 * Parse the name out of this packet.
		 */
		isc_buffer_remaining(source, &r);
		isc_buffer_setactive(source, r.length);
		result = getname(name, source, msg, dctx);
		if (result != DNS_R_SUCCESS)
			return (result);

		/*
		 * Get type, class, ttl, and rdatalen.  Verify that at least
		 * rdatalen bytes remain.  (Some of this is deferred to
		 * later.)
		 */
		isc_buffer_remaining(source, &r);
		if (r.length < 2 + 2 + 4 + 2)
			return (DNS_R_UNEXPECTEDEND);
		rdtype = isc_buffer_getuint16(source);
		rdclass = isc_buffer_getuint16(source);

		/*
		 * If there was no question section, we may not yet have
		 * established a class.  Do so now.
		 */
		if (msg->state == DNS_SECTION_ANY) {
			if (rdclass == 0 || rdclass == dns_rdataclass_any)
				return (DNS_R_FORMERR);
			msg->rdclass = rdclass;
			msg->state = DNS_SECTION_QUESTION;
		}
		   
		/*
		 * If this class is different than the one in the question
		 * section, bail.
		 */
		if (msg->opcode != dns_opcode_update
		    && rdtype != dns_rdatatype_tsig
		    && msg->rdclass != rdclass)
			return (DNS_R_FORMERR);

		/*
		 * If it is a tsig, verify that it is in the additional data
		 * section, and switch sections for the rest of this rdata.
		 */
		if (rdtype == dns_rdatatype_tsig) {
			if (sectionid != DNS_SECTION_ADDITIONAL)
				return (DNS_R_FORMERR);
			if (rdclass != dns_rdataclass_any)
				return (DNS_R_FORMERR);
			section = &msg->sections[DNS_SECTION_TSIG];
			msg->tsigstart = recstart;
		}
		
		/*
		 * ... now get ttl and rdatalen, and check buffer.
		 */
		ttl = isc_buffer_getuint32(source);