FreeRTOS-Plus/Source/FreeRTOS-Plus-UDP/FreeRTOS_DNS.c - nest-detect/1.3/freertos - Git at Google

 /*
  * FreeRTOS+UDP V1.0.4
  * Copyright (C) 2017 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of
  * this software and associated documentation files (the "Software"), to deal in
  * the Software without restriction, including without limitation the rights to
  * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
  * the Software, and to permit persons to whom the Software is furnished to do so,
  * subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in all
  * copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
  * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
  * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
  * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  *
  * http://www.FreeRTOS.org
  * http://aws.amazon.com/freertos
  *
  * 1 tab == 4 spaces!
  */

 /* Standard includes. */
 #include <stdint.h>

 /* FreeRTOS includes. */
 #include "FreeRTOS.h"
 #include "task.h"
 #include "queue.h"
 #include "timers.h"

 /* FreeRTOS+UDP includes. */
 #include "FreeRTOS_UDP_IP.h"
 #include "FreeRTOS_IP_Private.h"
 #include "FreeRTOS_DNS.h"
 #include "FreeRTOS_Sockets.h"
 #include "NetworkInterface.h"
 #include "IPTraceMacroDefaults.h"

 /* Exclude the entire file if DNS is not enabled. */
 #if ipconfigUSE_DNS != 0

 #if( ipconfigBYTE_ORDER == FREERTOS_LITTLE_ENDIAN )
 	#define dnsOUTGOING_FLAGS				0x0001 /* Standard query. */
 	#define dnsTYPE							0x0100 /* A record (host address. */
 	#define dnsCLASS						0x0100 /* IN */
 	#define dnsDNS_PORT						0x3500
 	#define dnsONE_QUESTION					0x0100
 	#define dnsRX_FLAGS_MASK				0x0f80 /* The bits of interest in the flags field of incoming DNS messages. */
 	#define dnsEXPECTED_RX_FLAGS			0x0080 /* Should be a response, without any errors. */
 #else
 	#define dnsDNS_PORT						0x35
 	#define dnsONE_QUESTION					0x01
 	#define dnsFLAG_QUERY_RESPONSE_BIT		0x8000
 	#define dnsFLAG_OPERATION_CODE_BITS		0x7800
 	#define dnsFLAG_TRUNCATION_BIT			0x0200
 	#define dnsFLAG_RESPONSE_CODE_BITS		0x000f
 	#define dnsOUTGOING_FLAGS				0x0100 /* Standard query. */
 	#define dnsTYPE							0x0001 /* A record (host address. */
 	#define dnsCLASS						0x0001 /* IN */
 	#define dnsRX_FLAGS_MASK				0x800f /* The bits of interest in the flags field of incoming DNS messages. */
 	#define dnsEXPECTED_RX_FLAGS			0x8000 /* Should be a response, without any errors. */
 #endif /* ipconfigBYTE_ORDER */

 /* The maximum number of times a DNS request should be sent out if a response
 is not received, before giving up. */
 #define dnsMAX_REQUEST_ATTEMPTS		5

 /* If the top two bits in the first character of a name field are set then the
 name field is an offset to the string, rather than the string itself. */
 #define dnsNAME_IS_OFFSET			( ( uint8_t ) 0xc0 )

 /*
  * Create a socket and bind it to the standard DNS port number.  Return the
  * the created socket - or NULL if the socket could not be created or bound.
  */
 static xSocket_t prvCreateDNSSocket( void );

 /*
  * Create the DNS message in the zero copy buffer passed in the first parameter.
  */
 static size_t prvCreateDNSMessage( uint8_t *pucUDPPayloadBuffer, const char *pcHostName, uint16_t usIdentifier );

 /*
  * Simple routine that jumps over the NAME field of a resource record.
  */
 static uint8_t *prvSkipNameField( uint8_t *pucByte );

 /*
  * Process a response packet from a DNS server.
  */
 static uint32_t prvParseDNSReply( uint8_t *pucUDPPayloadBuffer, uint16_t usIdentifier );

 /*-----------------------------------------------------------*/

 #include "pack_struct_start.h"
 struct xDNSMessage
 {
 	uint16_t usIdentifier;
 	uint16_t usFlags;
 	uint16_t usQuestions;
 	uint16_t usAnswers;
 	uint16_t usAuthorityRRs;
 	uint16_t usAdditionalRRs;
 }
 #include "pack_struct_end.h"
 typedef struct xDNSMessage xDNSMessage_t;

 /*-----------------------------------------------------------*/

 uint32_t FreeRTOS_gethostbyname( const char *pcHostName )
 {
 static uint16_t usIdentifier = 0;
 struct freertos_sockaddr xAddress;
 static xSocket_t xDNSSocket = NULL;
 uint32_t ulIPAddress = 0UL;
 uint8_t *pucUDPPayloadBuffer;
 static uint32_t ulAddressLength;
 BaseType_t xAttempt;
 int32_t lBytes;
 size_t xPayloadLength;
 const size_t xExpectedPayloadLength = sizeof( xDNSMessage_t ) + strlen( pcHostName ) + sizeof( uint16_t ) + sizeof( uint16_t ) + 2; /* Two for the count of characters in the first subdomain part, and the string end byte */

 	if( xDNSSocket == NULL )
 	{
 		xDNSSocket = prvCreateDNSSocket();
 	}

 	if( xDNSSocket != NULL )
 	{
 		/* Generate a unique identifier for this query. */
 		usIdentifier++;

 		for( xAttempt = 0; xAttempt < dnsMAX_REQUEST_ATTEMPTS; xAttempt++ )
 		{
 			/* Get a buffer.  This uses a maximum delay, but the delay will be
 			capped to ipconfigMAX_SEND_BLOCK_TIME_TICKS so the return value
 			still needs to be tested. */
 			pucUDPPayloadBuffer = ( uint8_t * ) FreeRTOS_GetUDPPayloadBuffer( xExpectedPayloadLength, portMAX_DELAY );
 			if( pucUDPPayloadBuffer != NULL )
 			{
 				/* Create the message in the obtained buffer. */
 				xPayloadLength = prvCreateDNSMessage( pucUDPPayloadBuffer, pcHostName, usIdentifier );
 				iptraceSENDING_DNS_REQUEST();

 				/* Obtain the DNS server address. */
 				FreeRTOS_GetAddressConfiguration( NULL, NULL, NULL, &ulIPAddress );

 				/* Send the DNS message. */
 				xAddress.sin_addr = ulIPAddress;
 				xAddress.sin_port = dnsDNS_PORT;
 				ulIPAddress = 0;

 				if( FreeRTOS_sendto( xDNSSocket, pucUDPPayloadBuffer, xPayloadLength, FREERTOS_ZERO_COPY, &xAddress, sizeof( xAddress ) ) != 0 )
 				{
 					/* Wait for the reply. */
 					lBytes = FreeRTOS_recvfrom( xDNSSocket, &pucUDPPayloadBuffer, 0, FREERTOS_ZERO_COPY, &xAddress, &ulAddressLength );

 					if( lBytes > 0 )
 					{
 						/* The reply was received.  Process it. */
 						ulIPAddress = prvParseDNSReply( pucUDPPayloadBuffer, usIdentifier );

 						/* Finished with the buffer.  The zero copy interface
 						is being used, so the buffer must be freed by the
 						task. */
 						FreeRTOS_ReleaseUDPPayloadBuffer( ( void * ) pucUDPPayloadBuffer );

 						if( ulIPAddress != 0 )
 						{
 							/* All done. */
 							break;
 						}
 					}
 				}
 				else
 				{
 					/* The message was not sent so the stack will not be
 					releasing the zero copy - it must be released here. */
 					FreeRTOS_ReleaseUDPPayloadBuffer( ( void * ) pucUDPPayloadBuffer );
 				}
 			}
 		}
 	}

 	return ulIPAddress;
 }
 /*-----------------------------------------------------------*/

 static size_t prvCreateDNSMessage( uint8_t *pucUDPPayloadBuffer, const char *pcHostName, uint16_t usIdentifier )
 {
 xDNSMessage_t *pxDNSMessageHeader;
 uint8_t *pucStart, *pucByte;
 const uint16_t usARecordType = dnsTYPE, usClass = dnsCLASS;
 static const xDNSMessage_t xDefaultPartDNSHeader =
 {
 	0,					/* The identifier will be overwritten. */
 	dnsOUTGOING_FLAGS,	/* Flags set for standard query. */
 	dnsONE_QUESTION,	/* One question is being asked. */
 	0,					/* No replies are included. */
 	0,					/* No authorities. */
 	0					/* No additional authorities. */
 };

 	/* Copy in the const part of the header. */
 	memcpy( ( void * ) pucUDPPayloadBuffer, ( void * ) &xDefaultPartDNSHeader, sizeof( xDefaultPartDNSHeader ) );

 	/* Write in a unique identifier. */
 	pxDNSMessageHeader = ( xDNSMessage_t * ) pucUDPPayloadBuffer;
 	pxDNSMessageHeader->usIdentifier = usIdentifier;

 	/* Create the resource record at the end of the header.  First
 	find the end of the header. */
 	pucStart = pucUDPPayloadBuffer + sizeof( xDefaultPartDNSHeader );

 	/* Leave a gap for the first length bytes. */
 	pucByte = pucStart + 1;

 	/* Copy in the host name. */
 	strcpy( ( char * ) pucByte, pcHostName );

 	/* Mark the end of the string. */
 	pucByte += strlen( pcHostName );
 	*pucByte = 0x00;

 	/* Walk the string to replace the '.' characters with byte counts.
 	pucStart holds the address of the byte count.  Walking the string
 	starts after the byte count position. */
 	pucByte = pucStart;

 	do
 	{
 		pucByte++;

 		while( ( *pucByte != 0x00 ) && ( *pucByte != '.' ) )
 		{
 			pucByte++;
 		}

 		/* Fill in the byte count, then move the pucStart pointer up to
 		the found byte position. */
 		*pucStart = ( uint8_t ) ( ( uint32_t ) pucByte - ( uint32_t ) pucStart );
 		( *pucStart )--;

 		pucStart = pucByte;

 	} while( *pucByte != 0x00 );

 	/* Finish off the record. */
 	pucByte++;
 	memcpy( ( void * ) pucByte, &usARecordType, sizeof( uint16_t ) );
 	pucByte += sizeof( uint16_t );
 	memcpy( ( void * ) pucByte, &usClass, sizeof( uint16_t ) );
 	pucByte += sizeof( uint16_t );

 	/* Return the total size of the generated message, which is the space from
 	the last written byte to the beginning of the buffer. */
 	return ( ( uint32_t ) pucByte - ( uint32_t ) pucUDPPayloadBuffer );
 }
 /*-----------------------------------------------------------*/

 static uint8_t *prvSkipNameField( uint8_t *pucByte )
 {
 	/* Determine if the name is the fully coded name, or an offset to the name
 	elsewhere in the message. */
 	if( ( *pucByte & dnsNAME_IS_OFFSET ) == dnsNAME_IS_OFFSET )
 	{
 		/* Jump over the two byte offset. */
 		pucByte += sizeof( uint16_t );

 	}
 	else
 	{
 		/* pucByte points to the full name.  Walk over the string. */
 		while( *pucByte != 0x00 )
 		{
 			/* The number of bytes to jump for each name section is stored in the byte
 			before the name section. */
 			pucByte += ( *pucByte + 1 );
 		}

 		pucByte++;
 	}

 	return pucByte;
 }
 /*-----------------------------------------------------------*/

 static uint32_t prvParseDNSReply( uint8_t *pucUDPPayloadBuffer, uint16_t usIdentifier )
 {
 xDNSMessage_t *pxDNSMessageHeader;
 uint32_t ulIPAddress = 0UL;
 uint8_t *pucByte;
 uint16_t x, usDataLength;
 const uint16_t usARecordType = dnsTYPE;

 	pxDNSMessageHeader = ( xDNSMessage_t * ) pucUDPPayloadBuffer;

 	if( pxDNSMessageHeader->usIdentifier == usIdentifier )
 	{
 		if( ( pxDNSMessageHeader->usFlags & dnsRX_FLAGS_MASK ) == dnsEXPECTED_RX_FLAGS )
 		{
 			/* Start at the first byte after the header. */
 			pucByte = pucUDPPayloadBuffer + sizeof( xDNSMessage_t );

 			/* Skip any question records. */
 			pxDNSMessageHeader->usQuestions = FreeRTOS_ntohs( pxDNSMessageHeader->usQuestions );
 			for( x = 0; x < pxDNSMessageHeader->usQuestions; x++ )
 			{
 				/* Skip the variable length name field. */
 				pucByte = prvSkipNameField( pucByte );

 				/* Skip the type and class fields. */
 				pucByte += sizeof( uint32_t );
 			}

 			/* Search through the answers records. */
 			pxDNSMessageHeader->usAnswers = FreeRTOS_ntohs( pxDNSMessageHeader->usAnswers );
 			for( x = 0; x < pxDNSMessageHeader->usAnswers; x++ )
 			{
 				pucByte = prvSkipNameField( pucByte );

 				/* Is the type field that of an A record? */
 				if( memcmp( ( void * ) pucByte, ( void * ) &usARecordType, sizeof( uint16_t ) ) == 0 )
 				{
 					/* This is the required record.  Skip the type, class, and
 					time to live fields, plus the first byte of the data
 					length. */
 					pucByte += ( sizeof( uint32_t ) + sizeof( uint32_t ) + sizeof( uint8_t ) );

 					/* Sanity check the data length. */
 					if( *pucByte == sizeof( uint32_t ) )
 					{
 						/* Skip the second byte of the length. */
 						pucByte++;

 						/* Copy the IP address out of the record. */
 						memcpy( ( void * ) &ulIPAddress, ( void * ) pucByte, sizeof( uint32_t ) );
 					}

 					break;
 				}
 				else
 				{
 					/* Skip the type, class and time to live fields. */
 					pucByte += ( sizeof( uint32_t ) + sizeof( uint32_t ) );

 					/* Determine the length of the data in the field. */
 					memcpy( ( void * ) &usDataLength, ( void * ) pucByte, sizeof( uint16_t ) );
 					usDataLength = FreeRTOS_ntohs( usDataLength );

 					/* Jump over the data lenth bytes, and the data itself. */
 					pucByte += usDataLength + sizeof( uint16_t );
 				}
 			}
 		}
 	}

 	return ulIPAddress;
 }
 /*-----------------------------------------------------------*/

 static xSocket_t prvCreateDNSSocket( void )
 {
 static xSocket_t xSocket = NULL;
 struct freertos_sockaddr xAddress;
 BaseType_t xReturn;
 TickType_t xTimeoutTime = 200 / portTICK_RATE_MS;

 	/* This must be the first time this function has been called.  Create
 	the socket. */
 	xSocket = FreeRTOS_socket( FREERTOS_AF_INET, FREERTOS_SOCK_DGRAM, FREERTOS_IPPROTO_UDP );

 	/* Auto bind the port. */
 	xAddress.sin_port = 0;
 	xReturn = FreeRTOS_bind( xSocket, &xAddress, sizeof( xAddress ) );

 	/* Check the bind was successful, and clean up if not. */
 	if( xReturn != 0 )
 	{
 		FreeRTOS_closesocket( xSocket );
 		xSocket = NULL;
 	}
 	else
 	{
 		/* Set the send and receive timeouts. */
 		FreeRTOS_setsockopt( xSocket, 0, FREERTOS_SO_RCVTIMEO, ( void * ) &xTimeoutTime, sizeof( TickType_t ) );
 		FreeRTOS_setsockopt( xSocket, 0, FREERTOS_SO_SNDTIMEO, ( void * ) &xTimeoutTime, sizeof( TickType_t ) );
 	}

 	return xSocket;
 }

 #endif /* ipconfigUSE_DNS != 0 */
	/*
	* FreeRTOS+UDP V1.0.4
	* Copyright (C) 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy of
	* this software and associated documentation files (the "Software"), to deal in
	* the Software without restriction, including without limitation the rights to
	* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
	* the Software, and to permit persons to whom the Software is furnished to do so,
	* subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in all
	* copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
	* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
	* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
	* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
	* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
	*
	* http://www.FreeRTOS.org
	* http://aws.amazon.com/freertos
	*
	* 1 tab == 4 spaces!
	*/

	/* Standard includes. */
	#include <stdint.h>

	/* FreeRTOS includes. */
	#include "FreeRTOS.h"
	#include "task.h"
	#include "queue.h"
	#include "timers.h"

	/* FreeRTOS+UDP includes. */
	#include "FreeRTOS_UDP_IP.h"
	#include "FreeRTOS_IP_Private.h"
	#include "FreeRTOS_DNS.h"
	#include "FreeRTOS_Sockets.h"
	#include "NetworkInterface.h"
	#include "IPTraceMacroDefaults.h"

	/* Exclude the entire file if DNS is not enabled. */
	#if ipconfigUSE_DNS != 0

	#if( ipconfigBYTE_ORDER == FREERTOS_LITTLE_ENDIAN )
	#define dnsOUTGOING_FLAGS 0x0001 /* Standard query. */
	#define dnsTYPE 0x0100 /* A record (host address. */
	#define dnsCLASS 0x0100 /* IN */
	#define dnsDNS_PORT 0x3500
	#define dnsONE_QUESTION 0x0100
	#define dnsRX_FLAGS_MASK 0x0f80 /* The bits of interest in the flags field of incoming DNS messages. */
	#define dnsEXPECTED_RX_FLAGS 0x0080 /* Should be a response, without any errors. */
	#else
	#define dnsDNS_PORT 0x35
	#define dnsONE_QUESTION 0x01
	#define dnsFLAG_QUERY_RESPONSE_BIT 0x8000
	#define dnsFLAG_OPERATION_CODE_BITS 0x7800
	#define dnsFLAG_TRUNCATION_BIT 0x0200
	#define dnsFLAG_RESPONSE_CODE_BITS 0x000f
	#define dnsOUTGOING_FLAGS 0x0100 /* Standard query. */
	#define dnsTYPE 0x0001 /* A record (host address. */
	#define dnsCLASS 0x0001 /* IN */
	#define dnsRX_FLAGS_MASK 0x800f /* The bits of interest in the flags field of incoming DNS messages. */
	#define dnsEXPECTED_RX_FLAGS 0x8000 /* Should be a response, without any errors. */
	#endif /* ipconfigBYTE_ORDER */

	/* The maximum number of times a DNS request should be sent out if a response
	is not received, before giving up. */
	#define dnsMAX_REQUEST_ATTEMPTS 5

	/* If the top two bits in the first character of a name field are set then the
	name field is an offset to the string, rather than the string itself. */
	#define dnsNAME_IS_OFFSET ( ( uint8_t ) 0xc0 )

	/*
	* Create a socket and bind it to the standard DNS port number. Return the
	* the created socket - or NULL if the socket could not be created or bound.
	*/
	static xSocket_t prvCreateDNSSocket( void );

	/*
	* Create the DNS message in the zero copy buffer passed in the first parameter.
	*/
	static size_t prvCreateDNSMessage( uint8_t pucUDPPayloadBuffer, const char pcHostName, uint16_t usIdentifier );

	/*
	* Simple routine that jumps over the NAME field of a resource record.
	*/
	static uint8_t prvSkipNameField( uint8_t pucByte );

	/*
	* Process a response packet from a DNS server.
	*/
	static uint32_t prvParseDNSReply( uint8_t *pucUDPPayloadBuffer, uint16_t usIdentifier );

	/-----------------------------------------------------------/

	#include "pack_struct_start.h"
	struct xDNSMessage
	{
	uint16_t usIdentifier;
	uint16_t usFlags;
	uint16_t usQuestions;
	uint16_t usAnswers;
	uint16_t usAuthorityRRs;
	uint16_t usAdditionalRRs;
	}
	#include "pack_struct_end.h"
	typedef struct xDNSMessage xDNSMessage_t;

	/-----------------------------------------------------------/

	uint32_t FreeRTOS_gethostbyname( const char *pcHostName )
	{
	static uint16_t usIdentifier = 0;
	struct freertos_sockaddr xAddress;
	static xSocket_t xDNSSocket = NULL;
	uint32_t ulIPAddress = 0UL;
	uint8_t *pucUDPPayloadBuffer;
	static uint32_t ulAddressLength;
	BaseType_t xAttempt;
	int32_t lBytes;
	size_t xPayloadLength;
	const size_t xExpectedPayloadLength = sizeof( xDNSMessage_t ) + strlen( pcHostName ) + sizeof( uint16_t ) + sizeof( uint16_t ) + 2; /* Two for the count of characters in the first subdomain part, and the string end byte */

	if( xDNSSocket == NULL )
	{
	xDNSSocket = prvCreateDNSSocket();
	}

	if( xDNSSocket != NULL )
	{
	/* Generate a unique identifier for this query. */
	usIdentifier++;

	for( xAttempt = 0; xAttempt < dnsMAX_REQUEST_ATTEMPTS; xAttempt++ )
	{
	/* Get a buffer. This uses a maximum delay, but the delay will be
	capped to ipconfigMAX_SEND_BLOCK_TIME_TICKS so the return value
	still needs to be tested. */
	pucUDPPayloadBuffer = ( uint8_t * ) FreeRTOS_GetUDPPayloadBuffer( xExpectedPayloadLength, portMAX_DELAY );
	if( pucUDPPayloadBuffer != NULL )
	{
	/* Create the message in the obtained buffer. */
	xPayloadLength = prvCreateDNSMessage( pucUDPPayloadBuffer, pcHostName, usIdentifier );
	iptraceSENDING_DNS_REQUEST();

	/* Obtain the DNS server address. */
	FreeRTOS_GetAddressConfiguration( NULL, NULL, NULL, &ulIPAddress );

	/* Send the DNS message. */
	xAddress.sin_addr = ulIPAddress;
	xAddress.sin_port = dnsDNS_PORT;
	ulIPAddress = 0;

	if( FreeRTOS_sendto( xDNSSocket, pucUDPPayloadBuffer, xPayloadLength, FREERTOS_ZERO_COPY, &xAddress, sizeof( xAddress ) ) != 0 )
	{
	/* Wait for the reply. */
	lBytes = FreeRTOS_recvfrom( xDNSSocket, &pucUDPPayloadBuffer, 0, FREERTOS_ZERO_COPY, &xAddress, &ulAddressLength );

	if( lBytes > 0 )
	{
	/* The reply was received. Process it. */
	ulIPAddress = prvParseDNSReply( pucUDPPayloadBuffer, usIdentifier );

	/* Finished with the buffer. The zero copy interface
	is being used, so the buffer must be freed by the
	task. */
	FreeRTOS_ReleaseUDPPayloadBuffer( ( void * ) pucUDPPayloadBuffer );

	if( ulIPAddress != 0 )
	{
	/* All done. */
	break;
	}
	}
	}
	else
	{
	/* The message was not sent so the stack will not be
	releasing the zero copy - it must be released here. */
	FreeRTOS_ReleaseUDPPayloadBuffer( ( void * ) pucUDPPayloadBuffer );
	}
	}
	}
	}

	return ulIPAddress;
	}
	/-----------------------------------------------------------/

	static size_t prvCreateDNSMessage( uint8_t pucUDPPayloadBuffer, const char pcHostName, uint16_t usIdentifier )
	{
	xDNSMessage_t *pxDNSMessageHeader;
	uint8_t pucStart, pucByte;
	const uint16_t usARecordType = dnsTYPE, usClass = dnsCLASS;
	static const xDNSMessage_t xDefaultPartDNSHeader =
	{
	0, /* The identifier will be overwritten. */
	dnsOUTGOING_FLAGS, /* Flags set for standard query. */
	dnsONE_QUESTION, /* One question is being asked. */
	0, /* No replies are included. */
	0, /* No authorities. */
	0 /* No additional authorities. */
	};

	/* Copy in the const part of the header. */
	memcpy( ( void * ) pucUDPPayloadBuffer, ( void * ) &xDefaultPartDNSHeader, sizeof( xDefaultPartDNSHeader ) );

	/* Write in a unique identifier. */
	pxDNSMessageHeader = ( xDNSMessage_t * ) pucUDPPayloadBuffer;
	pxDNSMessageHeader->usIdentifier = usIdentifier;

	/* Create the resource record at the end of the header. First
	find the end of the header. */
	pucStart = pucUDPPayloadBuffer + sizeof( xDefaultPartDNSHeader );

	/* Leave a gap for the first length bytes. */
	pucByte = pucStart + 1;

	/* Copy in the host name. */
	strcpy( ( char * ) pucByte, pcHostName );

	/* Mark the end of the string. */
	pucByte += strlen( pcHostName );
	*pucByte = 0x00;

	/* Walk the string to replace the '.' characters with byte counts.
	pucStart holds the address of the byte count. Walking the string
	starts after the byte count position. */
	pucByte = pucStart;

	do
	{
	pucByte++;

	while( ( pucByte != 0x00 ) && ( pucByte != '.' ) )
	{
	pucByte++;
	}

	/* Fill in the byte count, then move the pucStart pointer up to
	the found byte position. */
	*pucStart = ( uint8_t ) ( ( uint32_t ) pucByte - ( uint32_t ) pucStart );
	( *pucStart )--;

	pucStart = pucByte;

	} while( *pucByte != 0x00 );

	/* Finish off the record. */
	pucByte++;
	memcpy( ( void * ) pucByte, &usARecordType, sizeof( uint16_t ) );
	pucByte += sizeof( uint16_t );
	memcpy( ( void * ) pucByte, &usClass, sizeof( uint16_t ) );
	pucByte += sizeof( uint16_t );

	/* Return the total size of the generated message, which is the space from
	the last written byte to the beginning of the buffer. */
	return ( ( uint32_t ) pucByte - ( uint32_t ) pucUDPPayloadBuffer );
	}
	/-----------------------------------------------------------/

	static uint8_t prvSkipNameField( uint8_t pucByte )
	{
	/* Determine if the name is the fully coded name, or an offset to the name
	elsewhere in the message. */
	if( ( *pucByte & dnsNAME_IS_OFFSET ) == dnsNAME_IS_OFFSET )
	{
	/* Jump over the two byte offset. */
	pucByte += sizeof( uint16_t );

	}
	else
	{
	/* pucByte points to the full name. Walk over the string. */
	while( *pucByte != 0x00 )
	{
	/* The number of bytes to jump for each name section is stored in the byte
	before the name section. */
	pucByte += ( *pucByte + 1 );
	}

	pucByte++;
	}

	return pucByte;
	}
	/-----------------------------------------------------------/

	static uint32_t prvParseDNSReply( uint8_t *pucUDPPayloadBuffer, uint16_t usIdentifier )
	{
	xDNSMessage_t *pxDNSMessageHeader;
	uint32_t ulIPAddress = 0UL;
	uint8_t *pucByte;
	uint16_t x, usDataLength;
	const uint16_t usARecordType = dnsTYPE;

	pxDNSMessageHeader = ( xDNSMessage_t * ) pucUDPPayloadBuffer;

	if( pxDNSMessageHeader->usIdentifier == usIdentifier )
	{
	if( ( pxDNSMessageHeader->usFlags & dnsRX_FLAGS_MASK ) == dnsEXPECTED_RX_FLAGS )
	{
	/* Start at the first byte after the header. */
	pucByte = pucUDPPayloadBuffer + sizeof( xDNSMessage_t );

	/* Skip any question records. */
	pxDNSMessageHeader->usQuestions = FreeRTOS_ntohs( pxDNSMessageHeader->usQuestions );
	for( x = 0; x < pxDNSMessageHeader->usQuestions; x++ )
	{
	/* Skip the variable length name field. */
	pucByte = prvSkipNameField( pucByte );

	/* Skip the type and class fields. */
	pucByte += sizeof( uint32_t );
	}

	/* Search through the answers records. */
	pxDNSMessageHeader->usAnswers = FreeRTOS_ntohs( pxDNSMessageHeader->usAnswers );
	for( x = 0; x < pxDNSMessageHeader->usAnswers; x++ )
	{
	pucByte = prvSkipNameField( pucByte );

	/* Is the type field that of an A record? */
	if( memcmp( ( void * ) pucByte, ( void * ) &usARecordType, sizeof( uint16_t ) ) == 0 )
	{
	/* This is the required record. Skip the type, class, and
	time to live fields, plus the first byte of the data
	length. */
	pucByte += ( sizeof( uint32_t ) + sizeof( uint32_t ) + sizeof( uint8_t ) );

	/* Sanity check the data length. */
	if( *pucByte == sizeof( uint32_t ) )
	{
	/* Skip the second byte of the length. */
	pucByte++;

	/* Copy the IP address out of the record. */
	memcpy( ( void * ) &ulIPAddress, ( void * ) pucByte, sizeof( uint32_t ) );
	}

	break;
	}
	else
	{
	/* Skip the type, class and time to live fields. */
	pucByte += ( sizeof( uint32_t ) + sizeof( uint32_t ) );

	/* Determine the length of the data in the field. */
	memcpy( ( void * ) &usDataLength, ( void * ) pucByte, sizeof( uint16_t ) );
	usDataLength = FreeRTOS_ntohs( usDataLength );

	/* Jump over the data lenth bytes, and the data itself. */
	pucByte += usDataLength + sizeof( uint16_t );
	}
	}
	}
	}

	return ulIPAddress;
	}
	/-----------------------------------------------------------/

	static xSocket_t prvCreateDNSSocket( void )
	{
	static xSocket_t xSocket = NULL;
	struct freertos_sockaddr xAddress;
	BaseType_t xReturn;
	TickType_t xTimeoutTime = 200 / portTICK_RATE_MS;

	/* This must be the first time this function has been called. Create
	the socket. */
	xSocket = FreeRTOS_socket( FREERTOS_AF_INET, FREERTOS_SOCK_DGRAM, FREERTOS_IPPROTO_UDP );

	/* Auto bind the port. */
	xAddress.sin_port = 0;
	xReturn = FreeRTOS_bind( xSocket, &xAddress, sizeof( xAddress ) );

	/* Check the bind was successful, and clean up if not. */
	if( xReturn != 0 )
	{
	FreeRTOS_closesocket( xSocket );
	xSocket = NULL;
	}
	else
	{
	/* Set the send and receive timeouts. */
	FreeRTOS_setsockopt( xSocket, 0, FREERTOS_SO_RCVTIMEO, ( void * ) &xTimeoutTime, sizeof( TickType_t ) );
	FreeRTOS_setsockopt( xSocket, 0, FREERTOS_SO_SNDTIMEO, ( void * ) &xTimeoutTime, sizeof( TickType_t ) );
	}

	return xSocket;
	}

	#endif /* ipconfigUSE_DNS != 0 */