File content as of revision 17:c976088bf39d:

// DNSClient.cpp 2013/8/27
#include "mbed.h"
#include "mbed_debug.h"
#include "DNSClient.h"
#include "UDPSocket.h"
#include "dnsname.h"
#include "wiznet.h"

#if DBG_DNS
#define DBG2(...) do{debug("[DNS]%p %d %s ", this,__LINE__,__PRETTY_FUNCTION__); debug(__VA_ARGS__); } while(0);
#else
#define DBG2(...) while(0);
#endif

static SocketAddress theDnsServer;

DNSClient::DNSClient() : m_state(MYNETDNS_START), m_udp(NULL) {
    m_ns = NULL;

    //default to google
    theDnsServer.set_ip_address("8.8.8.8"); // DNS
    theDnsServer.set_port(53); // DNS
}

DNSClient::DNSClient(NetworkStack *ns, const char* hostname) : m_state(MYNETDNS_START), m_udp(NULL) {
    m_hostname = hostname;
    m_ns       = ns;
    
    //default to google
    theDnsServer.set_ip_address("8.8.8.8"); // DNS
    theDnsServer.set_port(53); // DNS
}

DNSClient::DNSClient(NetworkStack *ns, SocketAddress* pHost) : m_state(MYNETDNS_START), m_udp(NULL) {
    m_ns = ns;

    //default to google
    theDnsServer.set_ip_address("8.8.8.8"); // DNS
    theDnsServer.set_port(53); // DNS
}

DNSClient::~DNSClient() {
    if (m_udp) {
        delete m_udp;
    }
}

int DNSClient::setup(NetworkStack *ns) {
    m_ns = ns;
    return 0;
}

bool DNSClient::set_server(const char* serverip, int port) {
    theDnsServer.set_ip_address(serverip); 
    theDnsServer.set_port(port);
    return true;
}

void DNSClient::callback()
{
    uint8_t buf[512];
    SocketAddress host;
    int len = m_udp->recvfrom(&host, (char*)buf, sizeof(buf));
    if (len < 0) {
        return;
    }
    if (memcmp(buf+0, m_id, 2) != 0) { //verify
        return;
    }
    
    int rcode = response(buf, len);
    if (rcode == 0) {
        m_state = MYNETDNS_OK;
    } else {
        m_state = MYNETDNS_NOTFOUND;
    }
}

int DNSClient::response(uint8_t buf[], int size) {
    int rcode = buf[3] & 0x0f;
    if (rcode != 0) {
        return rcode;
    }
    int qdcount = buf[4]<<8|buf[5];
    int ancount = buf[6]<<8|buf[7];
    int pos = 12;
    while(qdcount-- > 0) {
        dnsname qname(buf);
        pos = qname.decode(pos); // qname
        pos += 4; // qtype qclass
    }
    while(ancount-- > 0) {
        dnsname name(buf);
        pos = name.decode(pos); // name
        int type = buf[pos]<<8|buf[pos+1];
        pos += 8; // type class TTL  
        int rdlength = buf[pos]<<8|buf[pos+1]; pos += 2;
        int rdata_pos = pos;
        pos += rdlength;
        if (type == 1) { // A record
            m_ip = (buf[rdata_pos]<<24) | (buf[rdata_pos+1]<<16) | (buf[rdata_pos+2]<<8) | buf[rdata_pos+3];
            sprintf(m_ipaddr, "%d.%d.%d.%d", buf[rdata_pos],buf[rdata_pos+1],buf[rdata_pos+2],buf[rdata_pos+3]);
        }
#if DBG_DNS
        printf("%s", name.str.c_str());
        if (type == 1) {
            printf(" A %d.%d.%d.%d\n", 
                buf[rdata_pos],buf[rdata_pos+1],buf[rdata_pos+2],buf[rdata_pos+3]);
        } else if (type == 5) {
            dnsname rdname(buf);
            rdname.decode(rdata_pos);
            printf(" CNAME %s\n", rdname.str.c_str());
        } else {
            printf(" TYPE:%d", type);
            printfBytes(" RDATA:", &buf[rdata_pos], rdlength);
        }
#endif
    }
    return rcode;
}

int DNSClient::query(uint8_t buf[], int size, const char* hostname) {
    const uint8_t header[] = {
        0x00,0x00,0x01,0x00, // id=0x0000 QR=0 rd=1 opcode=0 rcode=0
        0x00,0x01,0x00,0x00, // qdcount=1 ancount=0
        0x00,0x00,0x00,0x00};// nscount=0 arcount=0 
    const uint8_t tail[] = {0x00,0x01,0x00,0x01}; // qtype=A qclass=IN
    memcpy(buf, header, sizeof(header));
    int t = rand();
    m_id[0] = t>>8;
    m_id[1] = t;
    memcpy(buf, m_id, 2); 
    dnsname qname(buf);
    int pos = qname.encode(sizeof(header), (char*)hostname);
    memcpy(buf+pos, tail, sizeof(tail));
    pos += sizeof(tail);
    return pos;
}

void DNSClient::resolve(const char* hostname) {
    if (m_udp == NULL) {
        m_udp = new UDPSocket;
        m_udp->open(m_ns);
    }
    m_udp->set_blocking(false);
    m_udp->bind(rand()&0x7fff);
    uint8_t buf[256];                
    int size = query(buf, sizeof(buf), hostname);
#if DBG_DNS
    printf("hostname:[%s]\n", hostname);
    printHex(buf, size);
#endif
    m_udp->sendto(theDnsServer, (char*)buf, size);
    m_interval.reset();
    m_interval.start();
}

void DNSClient::poll() {
#if DBG_DNS
    printf("%p m_state: %d, m_udp: %p\n", this, m_state, m_udp);
    wait_ms(400);
#endif
    switch(m_state) {
        case MYNETDNS_START:
            m_retry = 0;
            resolve(m_hostname);
            m_state = MYNETDNS_PROCESSING;
            break;
        case MYNETDNS_PROCESSING: 
            break;
        case MYNETDNS_NOTFOUND: 
            break;
        case MYNETDNS_ERROR: 
            break;
        case MYNETDNS_OK:
            DBG2("m_retry=%d, m_interval=%d\n", m_retry, m_interval.read_ms());
            break;
    }
    if (m_interval.read_ms() > 1000) {
        m_interval.stop();
        DBG2("timeout m_retry=%d\n", m_retry);
        if (++m_retry >= 2) {
            m_state = MYNETDNS_ERROR;
        } else {
            resolve(m_hostname);
            m_state = MYNETDNS_PROCESSING;
        }
    }
}

//tests for a valid IP address, returns 0 if invalid IP address format, returns ip address if valid
static uint32_t
isValidIP(const char* ip) {
    int i1, i2, i3, i4;
    int len = strlen(ip);

    if (len < 7) return 0;

    //count the number of dots, there must be 3
    int dotcount = 0;
    for (int i = 0; i < len; i++) {
        if (ip[i] == '.' ) dotcount++;
    }

    //there must be exactly 3 dots
    if (dotcount != 3) return 0;

    sscanf((char*)ip, "%d.%d.%d.%d", &i1, &i2, &i3, &i4);

    if (strlen(ip) <= 16 && (i1 >= 0 && i1 <= 255) && (i2 >= 0 && i2 <= 255) &&
            (i3 >= 0 && i3 <= 255) && (i4 >= 0 && i4 <= 255)) {
        return ((i1<<24) | (i2<<16) | (i3<<8) | i4);
    }
    return 0;
}

bool DNSClient::lookup(const char* hostname) {
    m_hostname = hostname;
    
    uint32_t ip = isValidIP(hostname);

    //check if hostname is an IP address
    if (ip > 0) {
        //if it is already an IP address just return immediately
        m_ip = ip;
        strcpy(m_ipaddr, hostname);
        m_state = MYNETDNS_OK;
        return true;
    }
    
    m_state = MYNETDNS_START;
    while(1) {
        poll();
        callback();
        if (m_state != MYNETDNS_PROCESSING) {
            break;
        } 
    }
    
    if (m_udp) {
        delete m_udp;
        m_udp = NULL;
    }
    return m_state == MYNETDNS_OK;
}