From Computer Networking and Applications, Douglas Comer, Chapter 3

“To demonstrate network programming, we have devised a straightforward API for network communication.”

Comer’s API is an abstraction that simplifies the so-called socket programming API. (The socket API is the standard method applications use to enable themselves to use an IP network.)

/* echoclient.c */

#include <stdlib.h>

#include <stdio.h>

#include <cnaiapi.h>

#define BUFFSIZE 256

#define INPUT_PROMPT "Input > "

#define RECEIVED_PROMPT "Received> "

int readln(char *, int);

/*-----------------------------------------------------------------------

*

* Program: echoclient

* Purpose: contact echoserver, send user input and print server response

* Usage: echoclient <compname> [appnum]

* Note: Appnum is optional. If not specified the standard echo appnum

* (7) is used.

*

*-----------------------------------------------------------------------

*/

int

main(int argc, char *argv[])

{

computer comp;

appnum app;

connection conn;

char buff[BUFFSIZE];

int expect, received, len;

if (argc < 2 || argc > 3) {

(void) fprintf(stderr, "usage: %s <compname> [appnum]\n",

argv[0]);

exit(1);

}

/* convert the arguments to binary format comp and appnum */

comp = cname_to_comp(argv[1]);

if (comp == -1)

exit(1);

if (argc == 3)

app = (appnum) atoi(argv[2]);

else

if ((app = appname_to_appnum("echo")) == -1)

exit(1);

/* form a connection with the echoserver */

conn = make_contact(comp, app);

if (conn < 0)

exit(1);

(void) printf(INPUT_PROMPT);

(void) fflush(stdout);

/* iterate: read input from the user, send to the server, */

/* receive reply from the server, and display for user */

while((len = readln(buff, BUFFSIZE)) > 0) {

/* send the input to the echoserver */

(void) send(conn, buff, len, 0);

(void) printf(RECEIVED_PROMPT);

(void) fflush(stdout);

/* read and print same no. of bytes from echo server */

expect = len;

for (received = 0; received < expect;) {

len = recv(conn, buff, (expect - received) < BUFFSIZE ?

(expect - received) : BUFFSIZE, 0);

if (len < 0) {

send_eof(conn);

return 1;

}

(void) write(STDOUT_FILENO, buff, len);

received += len;

}

(void) printf("\n");

(void) printf(INPUT_PROMPT);

(void) fflush(stdout);

}

/* iteration ends when EOF found on stdin */

(void) send_eof(conn);

(void) printf("\n");

return 0;

}