/* Operating Systems Spring 2005
   Sample TCP sockets server

   This server accepts requests for information about a user 
    specified by userid or by username. The server uses the
	password database (getpwent) to look up and return information
    about a user.

  The complete protocol is described in the file PROTOCOL
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h> /* socket specific definitions */
#include <netinet/in.h> /* INET constants and stuff */
#include <arpa/inet.h>  /* IP address conversion stuff */
#include <netdb.h>	    /* gethostbyname */
#include <string.h>
#include <pwd.h>		/* password database */
#include "getline.h"	

/* set up a passive server socket.
   This returns the socket descriptor (any errors are 
   considered fatal).
   The function also prints out the port number assigned.
*/

int create_listening_socket() {
  struct sockaddr_in skaddr;
  int ld;
  int len;
 
  /* create a socket
       IP protocol family (PF_INET)
       TCP protocol (SOCK_STREAM)
  */
   
  if ((ld = socket( PF_INET, SOCK_STREAM, 0 )) < 0) {
    perror("Problem creating socket\n");
    exit(1);
  }
   
  /* establish our address
   address family is AF_INET
   our IP address is INADDR_ANY (any of our IP addresses)
   the port must be in network byte order!
  */
 
  skaddr.sin_family = AF_INET;
  skaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  skaddr.sin_port = htons(0);
 
  if (bind(ld, (struct sockaddr *) &skaddr, sizeof(skaddr))<0) {
    perror("Problem binding\n");
    exit(0);
  }

  /* find out what port number we have been assigned, and
	 print it out (to stdout)
  */

  len = sizeof(struct sockaddr);
  getsockname(ld,(struct sockaddr*)&skaddr,&len);
  printf("Port number assigned is %d\n",ntohs(skaddr.sin_port)); 

  /* put the socket into passive mode (waiting for connections) */
  if (listen(ld,5) < 0 ) {
    perror("Error calling listen\n");
    exit(1);
  }
                                                  
  return(ld);
}

/* send an error message back to the client */
int send_error(int client, char *msg) {
  char buf[strlen(msg)+10];

  sprintf(buf,"ERR %s\n",msg);
  return(writeline(client,buf));
}

/* send back the user info found */
/* "OK" followed by the user's full name */
int send_reply(int client, char *msg) {
  char buf[strlen(msg)+10];

  sprintf(buf,"OK %s\n",msg);
  return(writeline(client,buf));
}


/* Here is the code that handles a single client.
   The descriptor passed in is an active TCP socket
   connected to the client.
*/

void server(int client) {
  char buf[100];
  char username[100];
  unsigned int userid;
  struct passwd *p;

  /* read request from the client (one line of text) */
  if (getline(client,buf,99)<=0) {
	/* something bad has happened - we didn't get a complete line */
	return;
  }
  
  /* parse the request line, we expect either
	 "userid <number>"  -or-  "username <name>"
  */
  if (strncmp(buf,"username",7)==0) {
	strcpy(username,buf+9);
	p = getpwnam(username);
  } else if (strncmp(buf,"userid",6)==0) {
	userid = atoi(buf+7);
	p = getpwuid(userid);
  } else {
	/* invalid command */
	send_error(client,"Unrecognized command");
	return;
  }

  if (! p) {
	/* didn't find the user in the password database */
	send_error(client,"No such user");
	return;
  }

  /* seems we have a valid command, and we have found the
	 user. We send back the result as OK followed by the user's name
	 all on one line */

  send_reply(client,p->pw_gecos);
}
  
  
  



int main() {
  int ld,client;
  int addrlen;
  struct sockaddr_in from;

  /* create passive mode (listening) socket */

  ld = create_listening_socket();

  /* Here is the main server loop. It accepts a new connection
	 and handles the client. Once the request is done,
	 this server looks for the next client.
  */
  while (1) {
    printf("Ready for a connection...\n");
    addrlen=sizeof(from);
    if ( (client = accept( ld, (struct sockaddr*) &from, &addrlen)) < 0) {
      perror("Problem with accept call");
      exit(1);
    }
    /* call the server function to handle the connection */
    server(client);
	close(client);
  }
}