Network  Programming-TCP Sockets
(lecture programs)

Simple tcp Server & Client

server:

ª Creates a server socket,

ª Binds it to a port (e.g., 10101),

ª Receives a message from a client and displays it.

client:

ª Creates a client socket,

ª Connect to server at <host> <port> (e.g., localhost and 10101)

ª Sends "Hi" repeatedly out of this socket to the server.

tcpServer.c

 
#include "def"
main()
{
 int sd, psd;
 struct sockaddr_in name;
 char buf[1024];
 int cc;
 
 sd = socket (AF_INET,SOCK_STREAM,0);
 
 name.sin_family = AF_INET;
 name.sin_addr.s_addr = htonl(INADDR_ANY);
 name.sin_port = htons(atoi( argv[1] ));
 
 bind( sd, (SA *) &name, sizeof(name) );
 
 listen(sd,1);
 
 psd = accept(sd, 0, 0); 
 
 for(;;) {
 
  cc=recv(psd,buf,sizeof(buf), 0) ;
 
 if (cc == 0) exit (0);
  buf[cc] = NULL;
  printf("message received: %s\n", buf);
 }
}
 
Usage example:




 
 
% tcpServer0 10101
 
tcpClient.c

#include "def"
 
main(argc, argv )
int argc;
char *argv[];
 
{
 int sd;
 struct sockaddr_in server;
 struct hostent *hp, *gethostbyname();
 
 sd = socket (AF_INET,SOCK_STREAM,0);
 
 hp = gethostbyname( argv[1] );
 
 bcopy ( hp->h_addr, &(server.sin_addr.s_addr), hp->h_length);
 server.sin_family = AF_INET;
 server.sin_port = htons( atoi( argv[2] ) );
 
 connect(sd, (SA *) &server, sizeof(server));
 
 for (;;) {
 
  send(sd, "HI", 2, 0 );
 
 printf("sent HI\n");
 sleep(2);
 }
}

Usage example:

% tcpClient0 localhost 10101

---

Comprehensive tcp Client & Server

server:

ª Creates a server socket,

ª Binds it to a port. The port can be specified using either:

· Argument to the program (e.g., argv[1]), or

· Choosen by the system (0) and displayed after bind, useing getsockname.

ª Receives a message from a client and displays:

· The received message,

· The ip/name of the client,  and

· The port information of the client.

ª Sends (echo back) the received message to its sender.

client:

ª Creates a client socket and contacts the server using two arguments: <host> <port>

ª Sends to the server a message typed by the user.

ª Recieves from the server the echoed message and displays it along with the ip/name and port information of the server.

TCPServer.c

 
main( ... )
{ .....




 
 
/*get TCPServer1 Host information: NAME and INET ADDRESS*/
gethostname(ThisHost, MAXHOSTNAME);
printf("TCP/Server running at host NAME: %s\n", ThisHost);
hp = gethostbyname(ThisHost));
bcopy ( hp->h_addr, &(server.sin_addr), hp->h_length);
printf(" (TCP/Server INET ADDRESS is: %s )\n", inet_ntoa(server.sin_addr));




 
 
/* Construct name of socket */ 
server.sin_family = AF_INET;  
server.sin_addr.s_addr = htonl(INADDR_ANY); 
if (argc == 1) 
server.sin_port = htons(0) 
else 
{ 
server.sin_port = htons(atoi(argv[1])); 
}
 
/* Create socket on which to send and receive */
sd = socket (AF_INET,SOCK_STREAM,0); 
bind( sd, (SA *) &server, sizeof(server);
 
/* get port information and prints it out */
length = sizeof(server);
getsockname (sd, (SA *)&server,&length);
printf("Server Port is: %d\n", ntohs(server.sin_port));
 
/* accept TCP connections & fork a process to serve each client */
 listen(sd,4);
 fromlen = sizeof(from);
 for(;;){
 psd = accept(sd, (SA *)&from, &fromlen);
 childpid = fork();
 if ( childpid == 0) {
 close (sd);
 EchoServe(psd, from);
 }
 else{
 printf("My new child pid is %d\n", childpid);
 close(psd);
 }
 }
}/*end of main*/




 
 
 
EchoServe(int psd, struct sockaddr_in from){ 
 ....
 
/* print client information */
 printf("Serving %s:%d\n",inet_ntoa(from.sin_addr), ntohs(from.sin_port));
 hp = gethostbyaddr((char *) &from.sin_addr.s_addr, sizeof(from.sin_addr.s_addr),AF_INET)); 
 printf("(Name is : %s)\n", hp->h_name); 




 
 
/* get data from clients and send it back */
 for(;;){
 rc=recv(psd, buf, sizeof(buf), 0);
 if (rc > 0){
 buf[rc]=NULL; 
 printf("Received: %s\n", buf); 
 printf("From TCP/Client: %s:%d\n", 
 inet_ntoa(from.sin_addr), ntohs(from.sin_port)); 
  printf("(Name is : %s)\n", hp->h_name); 
 send(psd, buf, rc, 0); 
 }else { 
 printf("Disconnected..\n"); 
 close (psd); 
 exit(0);
 }
 }

}/End of EchoServ */
 
 
Usage example:




 
 % TCPServer1




 
 % TCPServer1 10101

TCPClient.c

main( ..)
{
....

/*get TCPClient1 Host information, NAME and INET ADDRESS */

gethostname(ThisHost, MAXHOSTNAME);
printf("TCP/Cleint running at host NAME: %s\n", ThisHost);
hp = gethostbyname(ThisHost));
bcopy ( hp->h_addr, &(server.sin_addr), hp->h_length);
printf(" (TCP/Cleint INET ADDRESS is: %s )\n", inet_ntoa(server.sin_addr));

/* get TCPServer1 Host information, NAME and INET ADDRESS */

if ( (hp = gethostbyname( argv[1] )) == NULL ) {

addr.sin_addr.s_addr = inet_addr( argv[1] );
hp = gethostbyaddr((char *) &addr.sin_addr.s_addr, sizeof(addr.sin_addr.s_addr),AF_INET);

}
printf("TCP/Server running at host NAME: %s\n", hp->h_name);
bcopy ( hp->h_addr, &(server.sin_addr), hp->h_length);
printf(" (TCP/Server INET ADDRESS is: %s )\n", inet_ntoa(server.sin_addr));

/* Construct name of socket to send to. */

server.sin_family = AF_INET;
server.sin_port = htons(atoi( argv[2] ));

/* Create socket on which to send and receive */
sd = socket (AF_INET,SOCK_STREAM,0);

/** Connect to TCPServer1 */

connect(sd, (SA *) &server, sizeof(server));
fromlen = sizeof(from);
getpeername(sd,(SA *)&from,&fromlen);
printf("Connected to TCPServer1: ");
printf("%s:%d\n", inet_ntoa(from.sin_addr),

ntohs(from.sin_port));
hp = gethostbyaddr((char *) &from.sin_addr.s_addr,
sizeof(from.sin_addr.s_addr),AF_INET));
printf("(Name is : %s)\n", hp->h_name);
childpid = fork();
if (childpid == 0) {
GetUserInput();
}

/* receive it from SERVER, display it back to USER */

for(;;) {

recv(sd, rbuf, sizeof(rbuf), 0)) ;
printf(" Received: %s", rbuf);

}

}/* End of main */

/* get data from USER, send it SERVER */

GetUserInput(){

for(;;) {

printf("Type anything followed by RETURN, or type CTRL-D to exit\n");
rc=read(0,buf, sizeof(buf));
if (rc == 0) break;
send(sd, buf, rc, 0);

}
printf ("EOF... exit\n");
close(sd);
kill(getppid(), 9);
exit (0);

}

Usage example:




 
 % TCPClient1 localhost 10101

---

Concurrency using Select

n = select ( length, readset, writeset, exceptset, time)

values of time:

NULL indifinate wait
          0            no-wait  (poll)
T           wait T  (sec + micro-sec)

A socket in readset is ready when:

§ A connected socket has received data.

§ A listen socket has a connection ready to accept.

Macros:

§ FD_ZERO(&mask);

§ FD_SET(sd, &mask);

§ FD_CLR(psd, &mask);

§ if (FD_ISSET(sd, &mask)) ....

TCPServerSel.c

main( ... )

{ .....

/** accept TCP connections from clients and use select to serve each */

listen(sd, 4);

fromlen = sizeof(from);

for (i = 0; i < MAXCLIENTS; i++)

client[i] = -1; /* -1 indicates available entry */

FD_ZERO(&allset);

FD_SET(sd, &allset);

for (;;) {

readset = allset; /* structure assignment */

select(MAXCLIENTS, &readset, NULL, NULL, NULL);

if (FD_ISSET(sd, &readset)) { /* new client connection */

psd = accept(sd, (SA *) & from, &fromlen);

for (i = 0; i < MAXCLIENTS; i++)

if (client[i] < 0) {

client[i] = psd; /* save descriptor */

FD_SET(psd, &allset); /* add new descriptor to set */

break;

}

if (i == MAXCLIENTS) {

printf("too many clients");

exit(0);

}

}

for (i = 0; i <= MAXCLIENTS; i++) { /* check all clients for data */

if ((psd = client[i]) < 0)

continue;

if (FD_ISSET(psd, &readset))

EchoServe(psd, from, i);

}

}

}

EchoServe(psd, from, i)

int psd;

struct sockaddr_in from;

int i;

{

/** get data from clients and send it back */

printf("\n...server is waiting...\n");

if ((rc = recv(psd, buf, sizeof(buf), 0)) < 0) {

perror("receiving stream message");

}

if (rc > 0) {

if (send(psd, buf, rc, 0) < 0)

perror("sending stream message");

} else {

printf("Disconnected..\n");

FD_CLR(psd, &allset);

client[i] = -1;

close(psd);

}

}

---