hello_server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

void error_handling(char *message);

int main(int argc, char *argv[]){
  int serv_sock;
  int clnt_sock;

  struct sockaddr_in serv_addr;
  struct sockaddr_in clnt_addr;
  socklen_t clnt_addr_size;

  char message[] = "Hello World!";

  if(argc != 2){
    printf("Usage: %s <port>\n", argv[0]);
    exit(1);
  }

  // create socket
  serv_sock = socket(PF_INET , SOCK_STREAM, 0);
  if( serv_sock == -1 ){
    error_handling("socket() error");
  }

  memset(&serv_addr, 0 , sizeof(serv_addr));
  serv_addr.sin_family = AF_INET;
  serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
  serv_addr.sin_port = htons(atoi(argv[1]));

  // assign ip addr and port 
  if (bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1){
      error_handling("bind() error");
  }
  clnt_addr_size = sizeof(clnt_addr);

  // call listen to make socket to be acceptable
  if (listen(serv_sock, 5) == -1){
      error_handling("listen() error") ;
  }

  // wait until accpet a request
  clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_addr_size);
  if (clnt_sock == -1){
    error_handling("accept() error");
  }

  // write something to the socket
  write(clnt_sock, message, sizeof(message));
  close(clnt_sock);
  close(serv_sock);
  return 0;
  
}


void error_handling(char *message){
  fputs(message, stderr);
  fputc('\n', stderr);
  exit(1);
}