Question

I m developing program usin IPC socket communication between socket under linux (kernel version is 2.6.25.20)
here after the source code of the client.c and the server.c

client.c

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>

#define NSTRS       3           /* no. of strings  */
#define ADDRESS     "mysocket"  /* addr to connect */

/*
 * Strings we send to the server.
 */
char *strs[NSTRS] = {
    "This is the first string from the client.\n",
    "This is the second string from the client.\n",
    "This is the third string from the client.\n"
};

main()
{
    char c;
    FILE *fp;
    register int i, s, len;
    struct sockaddr_un saun;

    /*
     * Get a socket to work with.  This socket will
     * be in the UNIX domain, and will be a
     * stream socket.
     */
    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
        perror("client: socket");
        exit(1);
    }

    /*
     * Create the address we will be connecting to.
     */
    saun.sun_family = AF_UNIX;
    strcpy(saun.sun_path, ADDRESS);

    /*
     * Try to connect to the address.  For this to
     * succeed, the server must already have bound
     * this address, and must have issued a listen()
     * request.
     *
     * The third argument indicates the "length" of
     * the structure, not just the length of the
     * socket name.
     */
    len = sizeof(saun.sun_family) + strlen(saun.sun_path);

    if (connect(s, &saun, len) < 0) {
        perror("client: connect");
        exit(1);
    }

    /*
     * We'll use stdio for reading
     * the socket.
     */
    fp = fdopen(s, "r");

    /*
     * First we read some strings from the server
     * and print them out.
     */
    for (i = 0; i < NSTRS; i++) {
        while ((c = fgetc(fp)) != EOF) {
            putchar(c);

            if (c == '\n')
                break;
        }
    }

    /*
     * Now we send some strings to the server.
     */
    for (i = 0; i < NSTRS; i++)
        send(s, strs[i], strlen(strs[i]), 0);

    /*
     * We can simply use close() to terminate the
     * connection, since we're done with both sides.
     */
    close(s);

    exit(0);
}

server.c

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>

#define NSTRS       3           /* no. of strings  */
#define ADDRESS     "mysocket"  /* addr to connect */

/*
 * Strings we send to the client.
 */
char *strs[NSTRS] = {
    "This is the first string from the server.\n",
    "This is the second string from the server.\n",
    "This is the third string from the server.\n"
};

main()
{
    char c;
    FILE *fp;
    int fromlen;
    register int i, s, ns, len;
    struct sockaddr_un saun, fsaun;

    /*
     * Get a socket to work with.  This socket will
     * be in the UNIX domain, and will be a
     * stream socket.
     */
    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
        perror("server: socket");
        exit(1);
    }

    /*
     * Create the address we will be binding to.
     */
    saun.sun_family = AF_UNIX;
    strcpy(saun.sun_path, ADDRESS);

    /*
     * Try to bind the address to the socket.  We
     * unlink the name first so that the bind won't
     * fail.
     *
     * The third argument indicates the "length" of
     * the structure, not just the length of the
     * socket name.
     */
    unlink(ADDRESS);
    len = sizeof(saun.sun_family) + strlen(saun.sun_path);

    if (bind(s, &saun, len) < 0) {
        perror("server: bind");
        exit(1);
    }

    /*
     * Listen on the socket.
     */
    if (listen(s, 5) < 0) {
        perror("server: listen");
        exit(1);
    }

    /*
     * Accept connections.  When we accept one, ns
     * will be connected to the client.  fsaun will
     * contain the address of the client.
     */
    if ((ns = accept(s, &fsaun, &fromlen)) < 0) {
        perror("server: accept");
        exit(1);
    }

    /*
     * We'll use stdio for reading the socket.
     */
    fp = fdopen(ns, "r");

    /*
     * First we send some strings to the client.
     */
    for (i = 0; i < NSTRS; i++)
        send(ns, strs[i], strlen(strs[i]), 0);

    /*
     * Then we read some strings from the client and
     * print them out.
     */
    for (i = 0; i < NSTRS; i++) {
        while ((c = fgetc(fp)) != EOF) {
            putchar(c);

            if (c == '\n')
                break;
        }
    }

    /*
     * We can simply use close() to terminate the
     * connection, since we're done with both sides.
     */
    close(s);

    exit(0);
}

After building and running the client and the server I get an error from server in the accept phase and it print the following error server: accept: Invalid argument

the same application run without problem in an other linux system (kernel version 2.6.30)

How to fix the source code to make it run in the first platform?

Answer 1

if ((ns = accept(s, &fsaun, &fromlen)) < 0) {

You have to initialize fromlen before passing it to the function.

The addrlen argument is a value-result argument: the caller must
initialize it to contain the size (in bytes) of the structure
pointed to by addr; on return it will contain the actual size of the
peer address.

Something like:

fromlen = sizeof(fsaun);
/* And then accept. */

And the correct type for fromlen is socklen_t, not int.