/* hw2-simple-server.c: program to send a constant HTTP 404/501 response. */
/* compile with: gcc -Wall -o hw2-simple-server hw2-simple-server.c */

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

/* maximum size of a printed address -- if not defined, we define it here */
#ifndef INET6_ADDRSTRLEN
#define	INET6_ADDRSTRLEN	46
#endif /* INET6_ADDRSTRLEN */

#define BUFSIZE 1000

/* print a system error and exit the program */
static void error (char * s)
{
  perror (s);
  exit (1);
}

/* terminates the buffer with a null character and: */
/* returns 0 if the first line has not yet been read */
/* returns -1 if the first line fills (overflows) the buffer */
/* returns 1 if the first line has been read and starts with GET */
/* returns 2 if the first line has been read and starts with something else */
static int parse_request (char * buf, int len, int maxlen)
{
  if (len >= maxlen)   /* overflow */
    return -1;
  buf [len] = '\0';    /* terminate, i.e. make it into a C string */
  if (index (buf, '\n') == NULL)   /* not finished reading the first line */
    return 0;
  if (strncmp (buf, "GET", 3) == 0)
    return 1;
  return 2;
}


/* must be executed inline, so must be defined as a macro */
#define next_loop(s) { if (s >= 0) close (s); continue; }

int main (int argc, char ** argv)
{
  int port = 8080;  /* can be used without root privileges */
  int server_socket = socket (AF_INET, SOCK_STREAM, 0);
  if (server_socket < 0)
    error ("socket");

  struct sockaddr_in sin;
  sin.sin_family = AF_INET;
  sin.sin_port = htons (port);
  sin.sin_addr.s_addr = INADDR_ANY;
  struct sockaddr * sap = (struct sockaddr *) (&sin);
  printf ("starting HTTP server on port %d\n", port);
  if (bind (server_socket, sap, sizeof (sin)) != 0)
    error ("bind");

  listen (server_socket, 10);

  while (1) {   /* infinite server loop */
    struct sockaddr_storage from;
    struct sockaddr_in * from_sinp = (struct sockaddr_in *) (&from);
    struct sockaddr    * from_sap  = (struct sockaddr    *) (&from);
    socklen_t addrlen = sizeof (from);
    int sockfd = accept (server_socket, from_sap, &addrlen);
    if (sockfd < 0)
      error ("accept");
    if (from_sap->sa_family != AF_INET) {
      printf ("accepted connection in address family %d, only %d supported\n",
              from_sap->sa_family, AF_INET);
      next_loop (sockfd);
    }
    char prt [INET6_ADDRSTRLEN] = "unable to print";
    inet_ntop (AF_INET, &(from_sinp->sin_addr), prt, sizeof (prt));
    printf ("accepted a connection from %s\n", prt);

    char buf [BUFSIZE];
    int received = 0;
    while (parse_request (buf, received, sizeof (buf)) == 0) {
      int r = recv (sockfd, buf + received, sizeof (buf) - received, 0);
      if (r <= 0) {
        printf ("received %d\n", r);
        next_loop (sockfd);
      }
      received += r;
    }
    int parse = parse_request (buf, received, sizeof (buf));
    if (parse == -1) {  /* first line longer than buffer */
      printf ("error: first line longer than %ld\n", sizeof (buf));
      next_loop (sockfd);
    }
    char * code = "HTTP/1.0 404 Not Found\r\n";
    if (parse == 2)
      code = "HTTP/1.0 501 Not implemented\r\n";
    send (sockfd, code, strlen (code), 0);

    char date_buf [BUFSIZE];
    time_t now = time (NULL);
    char * time_str = asctime (gmtime (&now));
    snprintf (date_buf, sizeof (date_buf), "Date: %s\n", time_str);
    /* time_str ends with \n.  We replace it with \r to give \r\n */
    * (index (date_buf, '\n')) = '\r';
    send (sockfd, date_buf, strlen (date_buf), 0);

    char server_id [] = "Server: dummy HTTP server\r\n";
    send (sockfd, server_id, strlen (server_id), 0);
    send (sockfd, "\r\n", 2, 0);
    shutdown (sockfd, SHUT_WR);  /* not useful, since we close right away */
    close (sockfd);
  }
  return 0;
}