TCP Echo Test

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This is a simple TCP usage example. It is an echo test client that sends a message to the echo server and then prints out the reply. The echo protocol is defined in RFC 862. In short, we send a message to the server, and the server echos the exact same message back.


  • Add the the to the shell directory as xsh_echotest.c
  • Modify shell.c and shell.h to include the echotest command.
  • Modify the Makefile in the shell directory to include xsh_echotest.c and then make XINU from the compile directory
  • Boot XINU
  • Run netup command from the shell
  • Run echoclient from the shell with the arguments of the echoserver's ip and the message to be sent in quotes
    • eg: echoclient "Hello XINU World!"


#include <stddef.h>
#include <stdio.h>
#include <device.h>
#include <ether.h>
#include <tcp.h>
#include <string.h>

#define MSG_MAX_LEN 64
#define ECHO_PORT 7

 * Shell command (echotest) sends a message to an echo server per RFC 862.
 * It waits for a response, then prints out the reply from the echo server.
 * Expects args: echotest, echo server ip, Message to echo in quotes
 * @param nargs number of arguments in args array
 * @param args  array of arguments
 * @return non-zero value on error
shellcmd xsh_echotest(int nargs, char *args[])
    ushort dev = 0;
    char buf[MSG_MAX_LEN];

    char *dest = args[1];

    struct netaddr dst;
    struct netaddr *localhost;
    struct netif *interface;

    int len;

    /* Allocate a new TCP device */
    if ((ushort)SYSERR == (dev = tcpAlloc()))
        fprintf(stderr, "Client: Failed to allocate a TCP device.");
        return SYSERR;

    /* Look up local ip info */
    interface = netLookup((ethertab[0].dev)->num);
    if (NULL == interface)
        fprintf(stderr, "Client: No network interface found\r\n");
        return SYSERR;
    localhost = &(interface->ip);

    /* Change the destination to ipv4 */
    if (SYSERR == dot2ipv4(dest, &dst))
        fprintf(stderr, "Client: Failed to convert ip address.");
        return SYSERR;

    /* Open the TCP device with the destination and echo port*/
    if (SYSERR == open(dev, localhost, &dst, NULL, ECHO_PORT, TCP_ACTIVE))
        fprintf(stderr, "Client: Could not open the TCP device\r\n");
        return SYSERR;

    /* Send the message to the destination*/
    memcpy(buf, args[2], MSG_MAX_LEN);

    if(SYSERR == write(dev, buf, MSG_MAX_LEN))
        fprintf(stderr, "Client: Error writing packet to the network");
        return SYSERR;

    /* Read a response from the server */
    if(SYSERR != (len = read(dev, buf, MSG_MAX_LEN)))
        printf("Client: Got response - %s\r\n", buf);

    /* Close the device when done */

    return 0;