Multiple Client Versions

Because different hosts can run different versions of RPC servers, a client should be capable of accommodating the variations. For example, one server can run the old version of RUSERSPROG(RUSERSVERS_ORIG) while another server runs the newer version (RUSERSVERS_SHORT).

If the version on a server does not match the version number in the client creation call, clnt_call() fails with an RPCPROGVERSMISMATCH error. You can get the version numbers supported by a server and then create a client handle with the appropriate version number. Use either the routine in the following example, or clnt_create_vers(). See the rpc(3NSL) man page for more details.

Example 5-17 RPC Versions on Client Side

main()
{
    enum clnt_stat status;
    u_short num_s;
    u_int num_l;
    struct rpc_err rpcerr;
    int maxvers, minvers;
    CLIENT *clnt;
 
    clnt = clnt_create("remote", RUSERSPROG, RUSERSVERS_SHORT,
                         "datagram_v");
    if (clnt == (CLIENT *) NULL) {
        clnt_pcreateerror("unable to create client handle");
        exit(1);
    }
    to.tv_sec = 10;          /* set the time outs */
    to.tv_usec = 0;
 
    status = clnt_call(clnt, RUSERSPROC_NUM, xdr_void,
                      (caddr_t) NULL, xdr_u_short, 
                          (caddr_t)&num_s, to);
    if (status == RPC_SUCCESS) {    /* Found latest version number */
        printf("num = %d\n", num_s);
        exit(0);
    }
    if (status != RPC_PROGVERSMISMATCH) {    /* Some other error */
        clnt_perror(clnt, "rusers");
        exit(1);
    }
    /* This version not supported */
    clnt_geterr(clnt, &rpcerr);
    maxvers = rpcerr.re_vers.high;    /* highest version supported */
    minvers = rpcerr.re_vers.low;     /*lowest version supported */

    if (RUSERSVERS_SHORT < minvers || RUSERSVERS_SHORT > maxvers)
{
                              /* doesn't meet minimum standards */
        clnt_perror(clnt, "version mismatch");
        exit(1);
    }
    (void) clnt_control(clnt, CLSET_VERSION, RUSERSVERS_ORIG);
    status = clnt_call(clnt, RUSERSPROC_NUM, xdr_void,
                          (caddr_t) NULL, xdr_u_int, (caddr_t)&num_l, to);
    if (status == RPC_SUCCESS)
        /* We found a version number we recognize */
        printf("num = %d\n", num_l);
    else {
        clnt_perror(clnt, "rusers");
        exit(1);
    }
}