User Datagram Protocol

UDP (also known as User Datagram Protocol) is a stateless network protocol.

Examples

POSIX C

Client

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>

#define BUFLEN 256
#define PORT 7

int main(void)
{
  char buf [BUFLEN];
  struct sockaddr_in si; 

  int sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  int flags;

  si.sin_family = AF_INET;
  si.sin_port = PORT; // This contains the target port number, and is adjusted. 
  inet_aton("127.229.133.45", &si_other.sin_addr); // COnverts target IP to network byte order.  Other functions exist. 

  // In order:
  //  sockfd = socket descriptor
  //  buf = data buffer to send
  //  BUFLEN = size of data buffer.
  //  flags = flags used for the datagram.  Supported flags include MSG_EOR and MSG_OOB.
  //  si = socket information defined above (contains transport endpoint)
  //  sizeof si = size of the socket information structure. 
  flags = 0;
  sendto(sockfd, buf, BUFLEN, 0, &si, sizeof si)
}

This client sends a UDP packet containing the contents of the stack to a given destination. As UDP is a stateless protocol, there will be no information on whether or not the remote server received the packet, unless it replies.

Server

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>

#define BUFLEN 256
#define PORT 7

int main(void)
{
  char buf [BUFLEN];
  struct sockaddr_in si, si_remote; 

  int sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  int flags;

  si.sin_family = AF_INET;
  si.sin_port = PORT; // This contains the target port number, and is adjusted. 
  si.sin_addr.s_addr = htonl(INADDR_ANY); 

  bind(sockfd, &si, sizeof(si)); // Binds the inbound socket.

  // In order:
  //  sockfd = socket descriptor
  //  buf = data buffer for receiving data
  //  BUFLEN = size of data buffer.
  //  flags = flags used for the datagram.  Supported flags include MSG_EOR and MSG_OOB.
  //  si_remote = socket information for the inbound packet
  //  sizeof si_remove = size of the socket information structure. 
  // 
  // When a packet is received, it is 
  recvfrom(s, buf, BUFLEN, 0, &si_remote, sizeof(si_remote));
}