client.c

#include <stdio.h> //printf
#include <string.h> //memset
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <ctype.h>
#include <netinet/in.h>
#include <unistd.h>
#include <netdb.h>


#define SERVER "127.0.0.1"
#define BUFLEN 1024  //Max length of buffer
#define PORT 5060   //The port on which to send data

int main(int argc, char **argv)
{
    struct sockaddr_in si_other;
    int s,slen=sizeof(si_other);
    char buf[BUFLEN];
    char message[]= "REGISTER sip:127.0.0.1 SIP/2.0\nVia: SIP/2.0/UDP 127.0.0.1:5060;branch=z9hG4bKnashds7\nFrom: <sip:bob@127.0.0.1>;tag=as58f4201b\nCall-ID: 843817637684230@hefrst\nTo: <sip:bob@127.0.0.1>\nCSeq: 1 REGISTER\nContact: <sip:bob@127.10.10.1>\nAllow: INVITE,ACK,OPTIONS,BYE,CANCEL,SUBSCRIBE,NOTIFY,REFER,MESSAGE,INFO,PING\nExpires: 3600\r\n\r\n"; 
    
    if ( (s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
    {
       fprintf(stderr, "socket failed");
       exit(1);
    }
 
    memset((char *) &si_other, 0, sizeof(si_other));
    si_other.sin_family = AF_INET;
    si_other.sin_port = htons(PORT);
     
    if (inet_aton(SERVER , &si_other.sin_addr) == 0) 
    {
        fprintf(stderr, "inet_aton() failed\n");
        exit(1);
    }
 
    while(1)
    {
        if (sendto(s, message, strlen(message) , 0 , (struct sockaddr *) &si_other, slen)==-1)
        {
            fprintf(stderr, "sendto failed");
            exit(1);
        }
        //receive a reply and print it
        // GETS STUCK HERE
        //clear the buffer by filling null, it might have previously received data
        bzero(buf,BUFLEN);
        if (recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen) == -1)
        {
            fprintf(stderr, "recvfrom() failed");
            exit(1);
        }
    }
  if (close(s) < 0)
  {
    fprintf(stderr, "close() failed \n");
    exit(1);
  }
    return 0;
}