DnsProtocol.h

// Matt Wells, copyright Mar 2001

#ifndef GB_DNSPROTOCOL_H
#define GB_DNSPROTOCOL_H

#include "UdpProtocol.h"
#include "UdpSlot.h"

// DNS request datagram (in network/bigEndian order):
//
// unsigned        id: 16;
//
// // fields in third byte 
//
// unsigned        qr: 1;          /* response flag */
// unsigned        opcode: 4;      /* purpose of message */
// unsigned        aa: 1;          /* authoritative answer */
// unsigned        tc: 1;          /* truncated message */
// unsigned        rd: 1;          /* recursion desired */
//
// // fields in fourth byte 
//
// unsigned        ra: 1;          /* recursion available */
// unsigned        unused :1;      /* unused bits (MBZ as of 4.9.3a3) */
// unsigned        ad: 1;          /* authentic data from named */
// unsigned        cd: 1;          /* checking disabled by resolver */
// unsigned        rcode :4;       /* response code */
// unsigned        qdcount :16;    /* number of question entries */
// unsigned        ancount :16;    /* number of answer entries */
// unsigned        nscount :16;    /* number of authority entries */
// unsigned        arcount :16;    /* number of resource entries */
//
// // query record/entry 
//
// CCLLLLLL           L = length of label, C = compressed?
// ssssssss ........  s = label (or next 8 bits of offset if C is true)
// ........
// CCLLLLLL           L = length of label, C = compressed?
// ssssssss ........  s = label (or next 8 bits of offset if C is true)
// 00000000           0 = zero, no more labels
// tttttttt tttttttt  t = queryType
// cccccccc cccccccc  c = queryClass
//
// // other records/entries 
//
// CCLLLLLL           L = length of label, C = compressed?
// ssssssss ........  s = label (or next 8 bits of offset if C is true)
// ........
// CCLLLLLL           L = length of label, C = compressed?
// ssssssss ........  s = label (or next 8 bits of offset if C is true)
// 00000000           0 = zero, no more labels
// tttttttt tttttttt  t = queryType
// cccccccc cccccccc  c = queryClass
// TTTTTTTT TTTTTTTT  T = time to live (TTL)
// TTTTTTTT TTTTTTTT
// rrrrrrrr rrrrrrrr  r = resource data len
// dddddddd ........  d = resource data

class DnsProtocol : public UdpProtocol {
public:
	DnsProtocol() {
	}
	virtual ~DnsProtocol() {
	}

	// override some protocol-depenent datagram parsing funcs
	// override these 4 functions to suit your own protocol
	virtual int32_t getTransId( const char *peek, int32_t /*peekSize*/ ) {
		return ntohs( *(int16_t *)( peek ) );
	}

	// we never use acks in dns land
	virtual bool useAcks() {
		return false;
	}

	// this is the reply/response bit in dns-land
	virtual bool isReply( const char *peek, int32_t peekSize ) {
		if ( peekSize < 4 )
			return true;
		return peek[2] & 0x80;
	}

	virtual bool didWeInitiate( const char * peek, int32_t peekSize ) {
		return !isReply( peek, peekSize );
	}

	virtual bool hadError( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return false;
	}

	// should we remove headers from the UdpSlot::m_readBuf ?
	virtual bool stripHeaders() {
		return false;
	}

	// first 4 bytes should have the info we need for DNS reply processing
	virtual int32_t getMaxPeekSize() {
		return 4;
	}

	// . do we have errnos in a dns reply?
	// . TODO: investigate this
	// . returns 0 if hadError bit is NOT set
	// . otherwise, returns first 4 bytes of msg CONTENT as an errno
	virtual int32_t getErrno( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return 0;
	}

	// we don't use acks
	virtual bool isAck( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return false;
	}

	// we don't cancel signals
	virtual bool isCancelTrans( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return false;
	}

	virtual bool isNice( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return true;
	}

	// we never use more than 1 udp dgram for dns
	virtual int32_t getDgramNum( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return 0;
	}

	// . even though it may be less than this, we can assume it's full
	// . returns -1 if msg size is the length of the whole dgram
	virtual int32_t getMsgSize( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return -1;
	}

	// how many dgram in the msg?
	virtual int32_t getNumDgrams( int32_t /*msgSize*/, int32_t /*maxDgramSize*/ ) {
		return 1;
	}

	// TODO: i guess all msg types are 0 for now
	virtual unsigned char getMsgType( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return 0;
	}

	// consider for our purposes to be 0
	virtual int32_t getHeaderSize( const char * /*peek*/, int32_t /*peekSize*/ ) {
		return 0;
	}

	// given a msg to send, how big is the header?
	virtual int32_t getHeaderSize( int32_t /*msgSize*/ ) {
		return 0;
	}

	virtual int32_t getMaxMsgSize() {
		return DGRAM_SIZE_DNS;
	}

	// we don't make Acks so return a dgramSize of 0
	virtual int32_t makeAck( char * /*dgram*/, int32_t /*dgramNum*/, int32_t /*transId*/, bool /*weInitiated*/,
							 bool /*cancelTrans*/ ) {
		return 0;
	}

	// we store the 1 dgram in it's ready to send form
	virtual void setHeader( char * /*buf*/, int32_t /*msgSize*/, unsigned char /*msgType*/, int32_t /*dgramNum*/,
							int32_t /*transId*/, bool /*weInitiated*/, bool /*hadError*/, int32_t /*niceness*/ ) {
		return;
	}
};

#endif // GB_DNSPROTOCOL_H