File content as of revision 44:83ce5ace337b:

#include    "mbed.h"
#include  "dnshdr.h"
#include "dnsname.h"
#include     "net.h"
#include  "action.h"
#include     "dns.h"
#include     "log.h"
#include    "dhcp.h"
#include   "slaac.h"
#include      "io.h"
#include     "ip4.h"
#include     "ip6.h"

bool DnsServerTrace = false;

#define RECORD_NONE        0
#define RECORD_PTR4        1
#define RECORD_PTR6_LOCAL  2
#define RECORD_PTR6_GLOBAL 3
#define RECORD_A           4
#define RECORD_AAAA_LOCAL  5
#define RECORD_AAAA_GLOBAL 6

#define MAX_ANSWERS 4

//Set by 'initialise'
static char* p;               //Position relative to DnsHdrData and is updated while both reading questions and writing answers
static char  myFullName4[100]; //The name, adjusted to include the domain if needed by the protocol, used when reading and when writing
static int   myFullName4Length;
static char  myFullName6[100]; //The name, adjusted to include the domain if needed by the protocol, used when reading and when writing
static int   myFullName6Length;

//Set by readQuestions and used by answerQuestions
static int   answers[MAX_ANSWERS];
static int   answerCount = 0;
static bool  mdnsUnicastReply;

static int readQuestions()
{
    p = DnsHdrData;
    mdnsUnicastReply = false;
    
    //Get the questions
    answerCount = 0;
    for (int i = 0; i < DnsHdrQdcount; i++)
    {
        //Bomb out if there are too many answers
        if (answerCount >= MAX_ANSWERS)
        {
            if (DnsServerTrace) LogTimeF("DnsServer-readQuestions - exceeded %d answers\r\n", MAX_ANSWERS);
            break;
        }
        
        //Bomb out if we are tending to overrun the buffer
        if (p - DnsHdrPacket > 512)
        {
            if (DnsServerTrace) LogTimeF("DnsServer-readQuestions - overrunning the buffer\r\n");
            return -1;
        }
        
        //Node name
        int nameLength = DnsNameLength(p);
        if (!nameLength)
        {
            if (DnsServerTrace) LogTimeF("DnsServer-readQuestions namelength is zero\r\n");
            return -1;
        }
        bool nodeIsName4 = DnsNameComparePtr(p, myFullName4);
        bool nodeIsName6 = DnsNameComparePtr(p, myFullName6);
        bool nodeIsAddr4 = DnsNameCompareIp4(p, DhcpLocalIp);
        bool nodeIsLocl6 = DnsNameCompareIp6(p, SlaacLinkLocalIp);
        bool nodeIsGlob6 = DnsNameCompareIp6(p, SlaacGlobalIp);
        p += nameLength;                          //Skip past the name
                
        //Type
        p++ ;                                     //skip the first byte of the type
        char recordType = *p++;                   //read the record type
        
        //Class
        if (*p++ & 0x80) mdnsUnicastReply = true; //check the class 15th bit (UNICAST-RESPONSE)
        p++;                                      //skip the class
        
        //Handle the questions
        if (nodeIsName4 && recordType == DNS_RECORD_A   )   answers[answerCount++] = RECORD_A;
        if (nodeIsName6 && recordType == DNS_RECORD_AAAA) { answers[answerCount++] = RECORD_AAAA_LOCAL; answers[answerCount++] = RECORD_AAAA_GLOBAL; }
        if (nodeIsAddr4 && recordType == DNS_RECORD_PTR )   answers[answerCount++] = RECORD_PTR4;
        if (nodeIsLocl6 && recordType == DNS_RECORD_PTR )   answers[answerCount++] = RECORD_PTR6_LOCAL;
        if (nodeIsGlob6 && recordType == DNS_RECORD_PTR )   answers[answerCount++] = RECORD_PTR6_GLOBAL;
    }
    return 0;
}
static int addAnswers(int dnsProtocol)
{
    //Strip the questions if this is MDNS
    //if (dnsProtocol == DNS_PROTOCOL_MDNS) p = DnsHdrData; 
    
    //Go through each answer
    DnsHdrAncount = 0;
    for (int i = 0; i < answerCount; i++)
    {                
        //Bomb out if we are tending to overrun the buffer
        if (p - DnsHdrPacket > 512)
        {
            if (DnsServerTrace) LogTimeF("DnsServer-addAnswers - reply is getting too big\r\n");
            return -1;
        }
                
        //Encode the node name
        switch (answers[i])
        {
            case RECORD_A:           DnsNameEncodePtr(myFullName4,      &p); break;
            case RECORD_AAAA_LOCAL:  DnsNameEncodePtr(myFullName6,      &p); break;  
            case RECORD_AAAA_GLOBAL: DnsNameEncodePtr(myFullName6,      &p); break;
            case RECORD_PTR4:        DnsNameEncodeIp4(DhcpLocalIp,      &p); break;
            case RECORD_PTR6_LOCAL:  DnsNameEncodeIp6(SlaacLinkLocalIp, &p); break;
            case RECORD_PTR6_GLOBAL: DnsNameEncodeIp6(SlaacGlobalIp,    &p); break;
        }
        
        //Add the 16 bit type
        *p++ = 0;
        switch (answers[i])
        {
            case RECORD_A:           *p++ = DNS_RECORD_A;    break;
            case RECORD_AAAA_LOCAL:  *p++ = DNS_RECORD_AAAA; break;
            case RECORD_AAAA_GLOBAL: *p++ = DNS_RECORD_AAAA; break;
            case RECORD_PTR4:        *p++ = DNS_RECORD_PTR;  break;
            case RECORD_PTR6_LOCAL:  *p++ = DNS_RECORD_PTR;  break;
            case RECORD_PTR6_GLOBAL: *p++ = DNS_RECORD_PTR;  break;
        }
        
        //Add the class
        char mdns = dnsProtocol == DNS_PROTOCOL_MDNS ? 0x80 : 0; //Set the 15th bit (CACHE_FLUSH) of the class to 1 if MDNS
        *p++ = mdns; *p++ = 1;                                   //16 bit Class LSB QCLASS_IN = 1 - internet
        
        //Add the TTL
        *p++ =    0; *p++ = 0; *p++ = 4; *p++ = 0;               //32 bit TTL seconds - 1024
        
        
        //Add the 16 bit payload length
        *p++ = 0;
        switch (answers[i])
        {
            case RECORD_A:           *p++ =  4;                    break;
            case RECORD_AAAA_LOCAL:  *p++ = 16;                    break;
            case RECORD_AAAA_GLOBAL: *p++ = 16;                    break;
            case RECORD_PTR4:        *p++ = myFullName4Length + 2; break; //add a byte for the initial length and another for the terminating zero length
            case RECORD_PTR6_LOCAL:  *p++ = myFullName6Length + 2; break;
            case RECORD_PTR6_GLOBAL: *p++ = myFullName6Length + 2; break;
        }
        
        //Add the payload
        switch (answers[i])
        {
            case RECORD_A:           memcpy(p, &DhcpLocalIp,      4); p +=  4; break;
            case RECORD_AAAA_LOCAL:  memcpy(p, SlaacLinkLocalIp, 16); p += 16; break;
            case RECORD_AAAA_GLOBAL: memcpy(p, SlaacGlobalIp,    16); p += 16; break;
            case RECORD_PTR4:        DnsNameEncodePtr(myFullName4, &p);        break;
            case RECORD_PTR6_LOCAL:  DnsNameEncodePtr(myFullName6, &p);        break;
            case RECORD_PTR6_GLOBAL: DnsNameEncodePtr(myFullName6, &p);        break;
        }
        //Increment the number of good answers to send
        DnsHdrAncount++;
    }
    return 0;
}

int DnsServerHandleQuery(void (*traceback)(void), int dnsProtocol, int *pSize) //Received an mdns or llmnr query on port 5353 or 5355
{    
    if (*pSize > 512)
    {
        if (DnsServerTrace)
        {
            if (NetTraceNewLine) Log("\r\n");
            LogTimeF("DnsServer length %d too long\r\n",  *pSize );
            if (NetTraceStack) traceback();
        }
        return DO_NOTHING;
    }
    
    myFullName4Length = DnsMakeFullNameFromName(dnsProtocol, NetName4, sizeof(myFullName4), myFullName4);
    myFullName6Length = DnsMakeFullNameFromName(dnsProtocol, NetName6, sizeof(myFullName6), myFullName6);
    
    if (readQuestions()) return DO_NOTHING;
    if (!answerCount) return DO_NOTHING;
    
    if (DnsServerTrace)
    {
        if (NetTraceNewLine) Log("\r\n");
        LogTimeF("DnsServer received query\r\n");
        if (NetTraceStack) traceback();
        DnsHdrLog(dnsProtocol);
    }
    
    if (addAnswers(dnsProtocol)) return DO_NOTHING;
    
    DnsHdrIsReply         = true;
    DnsHdrIsAuthoritative = true;
    DnsHdrWrite();
    
    *pSize = p - DnsHdrPacket;
    
    if (DnsServerTrace) DnsHdrLog(dnsProtocol);

    int dest;
    if (dnsProtocol == DNS_PROTOCOL_MDNS && !mdnsUnicastReply) dest = MULTICAST_MDNS;
    else                                                       dest =   UNICAST;
    
    return ActionMakeFromDestAndTrace(dest, NetTraceStack && DnsServerTrace);
}