#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

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

#define BUFLEN      255
#define MLBUFLEN    (10 * BUFLEN)

#define ERR_MLECHO_SYNTAX "ERROR bad syntax for MLECHO\n"
#define ERR_UNKNOWN_CMD   "ERROR unknown command\n"

#define PANIC(where)  { perror(where); exit(-1); }

int readline(int sd, char *buf, int buflen)
{
  int n, rc;
  char c;

  for (n = 1; n < buflen; n++) {
    if ((rc = read(sd, &c, 1)) == 1) {
      *buf++ = c;
      if (c == '\n')
	break;
    } 
    else if (rc == 0) {
      if (n == 1)
	return 0;
      else
	break;
    } else
      return -1;
  }
  *buf = 0;
  return n;
}

void write_safe(int d, const void *buf, size_t nbytes) {
  
  if (write(d, buf, nbytes) < 0)
    PANIC("write");
}

int main(void) {

  int sd, csd, i, addrlen;
  struct sockaddr_in client_addr, local_addr;
  char buf[BUFLEN], info[BUFLEN], mlbuf[MLBUFLEN];

  if ((sd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    PANIC("soccket");
 
  bzero((void *) &local_addr, sizeof(struct sockaddr_in));
  local_addr.sin_family = AF_INET;
  local_addr.sin_port = htons(9000);
  local_addr.sin_addr.s_addr = INADDR_ANY;

  if (bind(sd, (struct sockaddr *) &local_addr, sizeof(struct sockaddr_in)) < 0)
    PANIC("bind");

  if (listen(sd, SOMAXCONN) < 0)
    PANIC("listen");

  while (1) {
    
    addrlen = sizeof(struct sockaddr);
    csd = accept(sd, (struct sockaddr*) &client_addr, &addrlen);

    while (1) {
      bzero((void *) buf, BUFLEN);

      if (readline(csd, (char *) &buf, BUFLEN) < 0)
	PANIC("readline");

      if (strncmp("ECHO ", buf, 5) == 0) {
	write_safe(csd, "REPLY ", 6);
	write_safe(csd, (char *) &buf[5], strlen(&buf[5]));
      }
      else if (strncmp("INFO", buf, 4) == 0) {
	bzero((void *) info, BUFLEN);
	sprintf(info, "YOURIP %s\n", inet_ntoa(client_addr.sin_addr));
	write_safe(csd, info, strlen(info));
      }
      else if (strncmp("MLECHO ", buf, 7) == 0) {
	if ((strlen(buf) == 10) && isdigit(buf[7])) /* 'MLECHO n' and \n */
	  {
	    int mlbufidx = 0, lines, rc;

	    lines = atoi(&buf[7]);
	    bzero((void *) mlbuf, MLBUFLEN);
	    for (i = 0; i < lines; i++) {
	      rc = readline(csd, (char *) &mlbuf[mlbufidx], MLBUFLEN-mlbufidx);
	      if (rc < 0)
		PANIC("readline")
	      else
		mlbufidx += rc;
	    }
	    bzero((void *) info, BUFLEN);
	    sprintf(info, "MLREPLY %d\n", lines);
	    write_safe(csd, info, strlen(info));
	    write_safe(csd, mlbuf, strlen(mlbuf));
	  }
	else 
	  write_safe(csd, ERR_MLECHO_SYNTAX, strlen(ERR_MLECHO_SYNTAX));
      }
      else if (strncmp("QUIT", buf, 4) == 0)
	break;
      else 
	write_safe(csd, ERR_UNKNOWN_CMD, strlen(ERR_UNKNOWN_CMD));
    }
    close(csd);
  }
  close(sd); /* wird nie erreicht */
}