在C中使用rpc将字符串作为参数传递

Question

I am trying to write a simple RPC program that takes a string as argument and returns its length to the calling program. I am using RPCGEN to generate the required stubs. The code is as follows: The prog.x file:

    program PROGRAM_PROG {
    version PROGRAM_VERS {
    int fun(string) = 1;    /* procedure number = 1 */
    } = 1;                          /* version number = 1 */
    } = 0x31234567;                     /* program number = 0x31234567 */

The client.c file:

    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    #include <rpc/rpc.h>    /* standard RPC include file */
    #include "prog.h"       /* this file is generated by rpcgen */
    #include "math.h"
    main(int argc, char *argv[])
    {
        CLIENT *cl;         /* RPC handle */
        char *server;
char *word;
int *lresult;      /* return value from bin_date_1() */

if (argc != 3) {
    fprintf(stderr, "usage: %s hostname\n", argv[0]);
    exit(1);
}

server = argv[1];
word = argv[2];

printf("%s======\n", server);
printf("%s======\n", word);
/*
 * Create client handle
 */

if ((cl = clnt_create(server, PROGRAM_PROG, PROGRAM_VERS, "udp")) == NULL) {
    /*
     * can't establish connection with server
     */
     clnt_pcreateerror(server);
     exit(2);
}

/*
 * First call the remote procedure "bin_date".
 */
printf("123\n");
if ( (lresult = fun_1(&word, cl)) == NULL) {
    clnt_perror(cl, server);
    exit(3);
}
printf("456\n");
printf("time on host %s = %d and look, word: %s\n",server, *lresult, word);


clnt_destroy(cl);         /* done with the handle */
exit(0);

}

and finally the serverproc.c file:

    #include <stdio.h>
    #include <time.h>
    #include <string.h>
    #include <stdlib.h>
    #include <rpc/rpc.h>
    #include "prog.h"


    int *fun_1(char **p, CLIENT *cl)
    {
    int len;
    int t;
    t = strlen(*p);

    return &t;
    }

    int * fun_1_svc(char **p, struct svc_req *cl){
    CLIENT *client;
    return(fun_1(0, client));
    }

The code compiles fine but on running it, it simply hangs and I have to use a Ctrl-C to end it. The problem probably lies in the serverproc.c file. What am I doing wrong?

Answer 1

It may be due to following reasons :

• Check if either rpcbind or portmap is installed else do

    sudo apt-get install rpcbind 

• If installed then do just one thing. : generate your client and server code using rpcgen only like follows :

    rpcgen prog.x -a 

It will generate sample client and server code for you.

• Just add few lines in client code and in server code, set the calculated length to static variable "result", (already there).
• Give it a try, it will work surely !!

Answer 2

The hang is due to the fact that the server is listening for client connection. Using ctrl+c terminates the server. This can be verified by adding a printf statement in serverproc.c and check if that gets printed in the server console whenever a client connection is tried upon. Also If your client just seems to be hanging, chances are you have not started the portmapper.

Commands to start portmapper

OS command Mac OS X

launchctl start com.apple.portmap 

Linux

/sbin/portmap

*BSD

/usr/sbin/rpcbind