Playing with sockets

gistfile1.cpp

/*
 * File:   main.cpp
 * Author: patrik
 *
 * Created on October 7, 2011, 12:14 PM
 */

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sstream>
#include <iomanip>

using namespace std;

typedef unsigned char uchar;
typedef unsigned int uint;
typedef unsigned long ulong;


#define DNS_PORT 53
#define BUFFER_SIZE 8092

typedef struct{
    uint m_id;
    uint m_qr;
    uint m_opcode;
    uint m_aa;
    uint m_tc;
    uint m_rd;
    uint m_ra;
    uint m_qdCount;
    uint m_anCount;
    uint m_nsCount;
    uint m_arCount;
    string m_qName;
    uint m_qType;
    uint m_qClass;
} dnsPacket;

static const uint QR_MASK = 0x8000;
static const uint OPCODE_MASK = 0x7800;
static const uint AA_MASK = 0x0400;
static const uint TC_MASK = 0x0200;
static const uint RD_MASK = 0x0100;
static const uint RA_MASK = 0x8000;
static const uint RCODE_MASK = 0x000F;


static const uint HDR_OFFSET = 12;

int get16bits(const char*& buffer){

    int value = static_cast<uchar> (buffer[0]);
    value = value << 8;
    value += static_cast<uchar> (buffer[1]);
    buffer += 2;

    return value;
}

string decode_qname(const char*& buffer)
{
    string m_qName;
    m_qName.clear();

    int length = *buffer++;
    while (length != 0) {
        for (int i = 0; i < length; i++) {
            char c = *buffer++;
            m_qName.append(1, c);
        }
        length = *buffer++;
        if (length != 0) m_qName.append(1,'.');
    }

    return m_qName;
}

dnsPacket decode(const char* buffer)
{

    dnsPacket packet;
    packet.m_id = get16bits(buffer);

    uint fields = get16bits(buffer);
    packet.m_qr = fields & QR_MASK;
    packet.m_opcode = fields & OPCODE_MASK;
    packet.m_aa = fields & AA_MASK;
    packet.m_tc = fields & TC_MASK;
    packet.m_rd = fields & RD_MASK;
    packet.m_ra = fields & RA_MASK;
    packet.m_qdCount = get16bits(buffer);
    packet.m_anCount = get16bits(buffer);
    packet.m_nsCount = get16bits(buffer);
    packet.m_arCount = get16bits(buffer);

    buffer += HDR_OFFSET;

    packet.m_qName = decode_qname(buffer);
    packet.m_qType = get16bits(buffer);
    packet.m_qClass = get16bits(buffer);
    return packet;
}


string queryAsString(dnsPacket packet)
{
    ostringstream text;
    text << "ID: " << showbase << hex << packet.m_id << endl << noshowbase;
    text << "\tfields: [ QR: " << packet.m_qr << " opCode: " << packet.m_opcode << " ]" << endl;
    text << "\tQDcount: " << packet.m_qdCount << endl;
    text << "\tANcount: " << packet.m_anCount << endl;
    text << "\tNScount: " << packet.m_nsCount << endl;
    text << "\tARcount: " << packet.m_arCount << endl;
    text << "QUERY {\t " << endl;
    text << "\tQname: " << packet.m_qName << endl;
    text << "\tQtype: " << packet.m_qType << endl;
    text << "\tQclass: " << packet.m_qClass;
    text << " }" << dec;

    return text.str();
}

/*
 *
 */
int main(int argc, char** argv)
{
    int sockfd, newsockfd, portno; // int statements
    socklen_t clilen;  // length of socket

    char buffer[BUFFER_SIZE]; // buffer

    struct sockaddr_in serv_addr, cli_addr; // structures for socket address, for server and client

     // try to create socket
    if((sockfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
    {
        perror("Cannot create socket");
        exit(1);
    }

    // Server socket structure
    memset(&serv_addr, 0, sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(DNS_PORT);

    // Bind the socket
    if(bind(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1)
    {
        perror("Cannot bind the socket");
        exit(1);
    }

    do
    {
        // Do receive
        clilen = sizeof(cli_addr);
        int recvBytes;
        if((recvBytes = recvfrom(sockfd, buffer, BUFFER_SIZE, 0, (struct sockaddr*) &cli_addr, &clilen)) == -1)
        {
            perror("receive error: ");
            exit(1);
        }

        string text = queryAsString(decode(buffer));

        // Print the connection
        cout << "Connection from: " << inet_ntoa(cli_addr.sin_addr) << endl;
        cout << "DNS query: " << text << endl;

    }while(true);



    return 0;
}