File content as of revision 2:816cbd922d3e:

/* Class: mDNSResponder
 * Copyright 1991, 2003, 2010 Dirk-Willem van Gulik <dirkx(at)apache(punto)org>
 *
 * License: Any BSD or ASF License.
 *
 * Rough and ready port of some mDNS code.
 *
 * Typical use is something like
 *
 * EthernetNetIf eth;
 * HTTPServer svr;
 * mDNSResponder mdns;
 *
 * int main()...
 *
 *   // get internet
 *   EthernetErr ethErr = eth.setup();
 *   ... etc ..
 *
 *   // set up some server
 *   svr.addHandler<SimpleHandler>("/"); //Default handler
 *   svr.bind(80); * *

 *  // Extract the IP address.
 *   IpAddr ip = eth.getIp();
 *   printf("mbed IP Address is %d.%d.%d.%d\r\n", ip[0], ip[1], ip[2], ip[3]);
 *
 *   // Announce ourselves.
 *   mdns.announce(ip, "fred", "_http._tcp", 80, "The Little Server that Could", "path=/demo");
 *
 *   while()... enter some run loop
 *   ...
 *
 *  This will cause http://fred.local./demo to be announced as 'The Little Server that Could'.
 *
 *  Or as another example: (http://files.dns-sd.org/draft-cheshire-dnsext-dns-sd.txt)
 *  and the various RFCs:
 *
 *     mdns.announce(ip, "_ssh._tcp", 22, SSH to Serial Gateway", NULL);
 *
 * CAVEAT - a lot of the buffer overrun and copy checks
 *          where removed; and this is not anywhere near
 *          threadsafve or sane. Not for production use.
 */
#include "lwip/opt.h"
#if LWIP_DNS /* don't build if not configured for use in lwipopts.h */

#include "mDNSResponder.h"
#include <stdio.h>

#ifndef DNS_RRTYPE_SRV
#define DNS_RRTYPE_SRV (33)
#endif

mDNSResponder::mDNSResponder() : NetService(false),
        moi_txt(NULL), moi_port(0), moi_ip(0),
        moi_name(NULL), moi_proto(NULL),
        moi_local_proto(NULL), moi_local_name(NULL), moi_local_pglue(NULL),
        announcer() {
    // nothing yet...
}

mDNSResponder::~mDNSResponder() {
    announcer.stop();
    close();
}

void mDNSResponder::announce(IpAddr ip, const char * ldn, const char * proto, uint16_t port, const char * name, char ** txt) {
    Host localhost(IpAddr(MCAST), MDNS_PORT, NULL /* fqdn */);

    m_pUDPSocket = new UDPSocket;
    m_pUDPSocket->bind(localhost);

    m_pUDPSocket->setOnEvent(this, &mDNSResponder::onUDPSocketEvent);

    moi_port = port;
    moi_txt = txt;
    moi_ip = ip;
    moi_proto = proto;
    moi_name = name;

    moi_local_proto = (char *)malloc(128);
    moi_local_name = (char *)malloc(128);
    moi_local_pglue = (char *)malloc(128);

#define LOCAL "local"
    snprintf(moi_local_proto,128,"%s.%s.", moi_proto, LOCAL);
    snprintf(moi_local_name,128,"%s.%s.", ldn, LOCAL);
    snprintf(moi_local_pglue,128,"%s.%s.%s.", moi_name,moi_proto, LOCAL);

    // Gratuis intro - and repeat such regularly..
    //
    mDNSResponder::sendReply(DNS_RRTYPE_PTR, 0, localhost);
    announcer.start();
}

void mDNSResponder::close() {
    m_pUDPSocket->resetOnEvent();
    m_pUDPSocket->close();
    delete m_pUDPSocket;
}



void mDNSResponder::poll() { //Called by NetServices
    if (announcer.read_ms() > 1000  * MDNS_INTERVAL) {

        Host mch(IpAddr(MCAST), MDNS_PORT, NULL);
        mDNSResponder::sendReply(DNS_RRTYPE_PTR, 0, mch);

        announcer.reset();
    }
}

char * index(char * str, char c) {
    for (;str && *str;str++) {
        if (*str == c) return str;
    };
    return NULL;
}

#ifndef THREADINGCOMPRESS
#ifndef MAXCACHEDNSLABELS
#define MAXCACHEDNSLABELS (10)
#endif
static int labelCacheCnt = 0;
static uint16_t _cache_off[MAXCACHEDNSLABELS];
static char * _cache_och[MAXCACHEDNSLABELS];
static char * labelCacheOffset = 0;

void initLabelCache(char * off) {
    labelCacheOffset = off;
    labelCacheCnt = 0;
    memset(_cache_off,0, sizeof(_cache_off)); // Rely on min value to be 12
};

uint16_t checkLabelCache(char * name) {
    for (int i=0; i < MAXCACHEDNSLABELS; i++)
        if (_cache_off[i] && !strcmp(_cache_och[i],name))
            return _cache_off[i];
    return 0;
};

void addLabelCache(char * p, char * name) {
    _cache_off[labelCacheCnt] = p - labelCacheOffset;
    _cache_och[labelCacheCnt] = name;

    labelCacheCnt++;
    // we intentionally do not wack the first entries - as they are the most
    // likely ones to be used.
    if (labelCacheCnt>=MAXCACHEDNSLABELS)
        labelCacheCnt = MAXCACHEDNSLABELS / 3;
};
#else
#define initLabelCache(x) {} /* Ignored */
#define checkLabelCache(x) (0) /* never a hit */
#define addLabelCache(x,y) {} /* Ignored */
#endif

char * breakname(char *p, char *name) {
    int l = 0, de = 1;
    char * q;
    uint16_t off;

    do {
        if ((off = checkLabelCache(name))) {
            *p++ = 192 + (off >> 8);
            *p++ =       (off &  0xFF);
            return p;
        } else {
            addLabelCache(p, name);
        };

        q = index(name,'.');
        if (!q) {
            q = name + strlen(name);
            de = 0;
        };
        l = q - name;
        *p++ = l;
        memcpy(p, name, l);
        p+=l;
        name = q + 1;
    } while (l && *name && de);

    // terminating root field if any (not the case for
    // things like TXTs).
    if (de) *p++ = 0;
    return p;
}

char * mRR(char *p, char * name, uint16_t tpe, uint16_t cls, uint32_t ttl) {
    uint16_t i = 0;
    uint32_t j = 0;

    p = breakname(p, name);

    // NOTE: Cannot assume proper byte boundaries.
    //
    i = htons(tpe); // Type
    memcpy(p, &i,  2);
    p+=2;

    i = htons(cls); // Class
    memcpy(p, &i, 2);
    p+=2;

    j = htonl(ttl); // TTL (4 bytes)
    memcpy(p, &j, 4);
    p+=4;

    return p;
}

char * mRRLABEL(char *p, char * name, uint16_t tpe, char ** rr) {
    uint16_t i;

    p = mRR(p, name, tpe, DNS_RRCLASS_IN, MDNS_TTL); // Type, IN, TTL

    // RR String
    char * q = p + 2;

    for (;*rr;rr++)
        q = breakname(q, *rr);

    i = htons(q - p - 2); // RDLEN
    memcpy(p, &i, 2);
    return q;
}

char * mPTR(char *p, char * name, char * r) {
    char *rr[] = { r, NULL };
    return mRRLABEL(p, name, DNS_RRTYPE_PTR, rr );
}

char * mTXT(char *p, char * name, char ** rr) {
    return mRRLABEL(p, name, DNS_RRTYPE_TXT, rr);
}

char * mARR(char *p, char * name, IpAddr ip) {
    uint16_t i;

    p = mRR(p, name, DNS_RRTYPE_A, DNS_RRCLASS_IN, MDNS_TTL ); // A, IN

    i = htons(4); // RDLEN - we're just doing a single IPv4 address - our primary link ?
    memcpy(p, &i, 2);

    // IP already in network order.
    memcpy(p+2, &ip, 4);

    return p + 2 + 4;
}

char * mSRV(char *p, char * name, uint16_t port, char * rr) {
    uint16_t i = 0;
    char * q;

    p = mRR(p, name, DNS_RRTYPE_SRV, DNS_RRCLASS_IN, MDNS_TTL); // SRV, IN

    // Keep space for RDLEN
    q = p;
    p+=2;

    i = htons(1); // Priority
    memcpy(p, &i, 2);
    p+=2;

    i = htons(0); // Weight (see rfc2782)
    memcpy(p, &i, 2);
    p+=2;

    i = htons(port); // Port
    memcpy(p, &i, 2);
    p+=2;

    p = breakname(p, rr);

    i = htons(p - q - 2); // RDLEN
    memcpy(q, &i, 2);

    return p;
}

char * qANY(char *p, char * name, uint16_t tpe, uint16_t cls) {
    uint16_t i = 0;
    p = breakname(p, name); // QNAME

    i = htons(tpe); // QTYPE
    memcpy(p, &i, 2);
    p+=2;

    i = htons(cls); // QCLASS
    memcpy(p, &i, 2);
    p+=2;

    return p;
}

char * qPTR(char *p, char *name) {
    return qANY(p,name,DNS_RRTYPE_PTR,DNS_RRCLASS_IN);
}

char * qA(char *p, char *name) {
    return qANY(p,name,DNS_RRTYPE_A,DNS_RRCLASS_IN);
}

char * qSRV(char *p, char *name) {
    return qANY(p,name,DNS_RRTYPE_SRV,DNS_RRCLASS_IN);
}

void mDNSResponder::sendReply(uint16_t t, uint16_t tid, Host dst) {
    // sent a reply - basically a precooked A/PTR/SRV with the TransactionID
    // and my URI squeezed in.
    char out[ 1500 ], *p;
    DNSPacket * op = (DNSPacket *) out;

    initLabelCache(out); // Offsets are relative to the ID header.

    op->tid = ntohs(tid);
    op->flags = ntohs(0x8000U); // Answer
    op->question_count = ntohs(1); // Courtesy copy of the question.
    op->answer_count = ntohs(1); // The record asked for
    op->a_count = ntohs(0);
    p = out + 12;
    
    switch(t) {
    case DNS_RRTYPE_PTR:    // PTR record, SRV, optional TXT and A with my own address.
         op->aa_count = ntohs(moi_txt ? 3 : 2);
        p = qPTR(p,moi_local_proto);
        
        p = mPTR(p,moi_local_proto, moi_local_pglue);
        if (moi_txt && * moi_txt)
            p = mTXT(p,moi_local_pglue,moi_txt);
            
        break;
    case DNS_RRTYPE_A:    // A record (and nothing else)
        op->aa_count = ntohs(1);
        p = qA(p,moi_local_name);
        break;

    case DNS_RRTYPE_SRV:   // SRV record and a gratious A record to complete.
        op->aa_count = ntohs(moi_txt ? 2 : 1);
        p = qSRV(p,moi_local_pglue);
        
        p = mPTR(p,moi_local_proto, moi_local_pglue);
        if (moi_txt && * moi_txt)
            p = mTXT(p,moi_local_pglue,moi_txt);
        break;
        }
    p = mARR(p,moi_local_name,moi_ip);     
    m_pUDPSocket->sendto(out,p-out,&dst);
}

char * decodeQBlock(char * udp, int len, char *p, char  * fqdn, int fqdn_size, uint32_t *Qclass, uint32_t *Qtype)
{
    char * endp = udp + len;
    int depth = 0;
    int l, ll = 0;
    char * q = 0;
    char * ep = fqdn;
    
    do {
        while (((l = *p++) < 192) && (l > 0)) 
        {
            if (p + l >= endp) {
                printf("RR longer than packet\r\n");
                return NULL;
            };
            
            if (ll + l + 1 > fqdn_size) {
                printf("FQDN too long\r\n");
                return NULL;
            }
            
            memcpy(ep,p,l);
            ep[l]='.';
            ep += l + 1;
            p += l;
            ll += l + 1;
        };

        if (l >= 192) {
            // construct an offset pointer by wiping the top 1 bits
            // and then getting the remaining 8 bytes to make 14.
            l -= 192;
            l = l << 8;
            l += *p++;
            
            // rescue our reference; as we've not gotten the Qt's yet
            // and these follow the last entry in our record (and not
            // that from the compressed values.
            //
            if (!q) q = p;

            // printf(" [->%d] ",l);
            p = udp + l;

            if (p >= udp + len || p < udp + 12) {
                printf("Pointer to wrong place\r\n");
                return NULL;
            };
        };
        
        if (depth++ >= 128) {
            printf("Far too deep\r\n");
            return NULL;
        };
    } while (l);
    
    // Terminate the FQDN string.
    *ep = 0;
    
    // in case no compression was used at all.
    if (!q) 
        q = p;

    *Qtype = htons(q[0] + q[1]*256);
    *Qclass = htons(q[2] + q[3]*256);
    return p;
}

void mDNSResponder::onUDPSocketEvent(UDPSocketEvent e) {
    char udp[ 1500 ];
    Host from;
    int len;

    switch (e) {
        case UDPSOCKET_READABLE: //The only event for now
            // parse through the packet; find any PTR requests
            // and respond to any for _http._tcp._local.
            while ((len = m_pUDPSocket->recvfrom( (char*)&udp, sizeof(udp), &from ))) {
                DNSPacket * dp = (DNSPacket *) udp;
                unsigned int tid = ntohs(dp->tid);
                unsigned int flags = ntohs(dp->flags);
                unsigned int nQ = ntohs(dp->question_count);
                // unsigned int nA = ntohs(dp->answer_count);

                if (flags & 2 != 0 || nQ == 0)
                    continue; // we only want questions

                // assume nQ NON terminated fields followed by Qtype & Qclass
                //
                char * p = udp + 12;
                for (int i = 0; i < nQ; i++) {
                    char fqdn[ 256 ];
                    uint32_t Qt, Qc;
                    
                    if (!((p = decodeQBlock(udp,len,p,fqdn,sizeof(fqdn),&Qc, &Qt))))
                        return;
                        
                    // We only deal with INternet.
                    //
                    if (Qc != DNS_RRCLASS_IN)
                        continue;
                    
                    printf("Q type %d for %s\r\n", Qt, fqdn);
                    
                    // We want PTR records on the INternet of our type. Also do ANY.
                    //
                    if ((Qt == DNS_RRTYPE_PTR || Qt == 255) && !(strcmp(fqdn,moi_local_proto)))
                        sendReply(DNS_RRTYPE_PTR,tid,from);
                    else if ((Qt == DNS_RRTYPE_A || Qt == 255)  && !(strcmp(fqdn,moi_local_name)))
                        sendReply(DNS_RRTYPE_A,tid,from);
                    else if ((Qt == DNS_RRTYPE_SRV || Qt == 255)  && !(strcmp(fqdn,moi_local_pglue)))
                        sendReply(DNS_RRTYPE_SRV,tid,from);
                };
            }
            break;
    }
}
#endif