sending a struct array with sun rpc from server to client

Question

how can i correctly send a struct from the server to the client in ansi-c sun-rpc?

in my test.x IDL file i defined a struct cluster with a string and an int and a type clusters which is a variable-length array of cluster elements:

struct cluster {
    string name<255>;
    int debuglevel;
};

typedef cluster clusters<32>;

i then changed the stubs generated by rpcgen like

test_server.c

clusters *
test_1_svc(void *argp, struct svc_req *rqstp)
{

    static clusters result;

    cluster cl1, cl2;

    cl1.name="cl1";
    cl1.debuglevel="1";
    cl2.name="cl2";
    cl2.debuglevel="2";

    cluster clist[2];

    clist[0]=cl1;
    clist[1]=cl2;

    result.clusters_len = 2;
    result.clusters_val = &clist;

    /*
     * insert server code here
     */

    return(&result);
}

and test_client.c

test_prog_1( char* host )
{
    CLIENT *clnt;
    clusters  *result_1;
    char*  test_1_arg;
    clnt = clnt_create(host, test_PROG, test_VERS, "udp");
    if (clnt == NULL) {
        clnt_pcreateerror(host);
        exit(1);
    }
    result_1 = test_1((void*)&test_1_arg, clnt);
    if (result_1 == NULL) {
        clusters* rec_cls = malloc(2*sizeof(struct cluster));
        if(xdr_clusters(&result_1, rec_cls)){
                printf("got xdr_clusters");
        }
        clnt_perror(clnt, "call failed:");
    }
    clnt_destroy( clnt );
}

Both compile, but the server often segfaults after one or two request runs by the client and on the clientside the xdr_clusters function never returns true. It seems like some kind of memory mismanagement and I'm also not sure if I'm handling the serialization on the server-side correctly.

I just filled result.clusters_len and result.clusters_val with the appropiate values like they are defined in test.h (by rpcgen):

typedef struct {
    u_int clusters_len;
    cluster *clusters_val;
} clusters;

Do I have to make use of xdr_clusters on the server side for this to correctly serialize the result?

thank you

score 0 · Accepted Answer · answered Nov 18 '15 at 11:04

okay, i figured my mistakes, lets summarize them:

know how to initialize an int correctly (without the quotes of course...)
forget about that clist nonsense, just malloc the internal pointer of the result struct directly
read the damn compiler warnings: when it tells you, that there are functions declared implicitly and you didn't want implicit declarations, then there is possibly something missing, in my case i needed to include stdlib.h and stdio.h to get malloc, printf and exit functions for server and client stubs.
on the clientside: why should we do anything except throwing an error if the result is NULL? see the new client code below to check correct result printing

test_server.c

    test_1_svc(void *argp, struct svc_req *rqstp){

        static clusters result;

        cluster cl1, cl2;

        cl1.name="cl1";
        cl1.debuglevel=1;
        cl2.name="cl2";
        cl2.debuglevel=2;

        result.clusters_len = 2;
        result.clusters_val = malloc(2*sizeof(struct cluster));

        result.clusters_val[0]=cl1;
        result.clusters_val[1]=cl2;

        return(&result);
    }

test_client.c

test_prog_1( char* host )
{
    CLIENT *clnt;
    clusters  *result_1;
    char*  test_1_arg;
    clnt = clnt_create(host, test_PROG, test_VERS, "udp");
    if (clnt == NULL) {
        clnt_pcreateerror(host);
        exit(1);
    }
    result_1 = test_1((void*)&test_1_arg, clnt);
    if (result_1 == NULL) {
        clnt_perror(clnt, "call failed:");
    }else{
        printf("I got %d cluster structs in an array\n",result_1->clusters_len);
        int j;
        for(j=0;j<result_1->clusters_len;j++){
            printf("cluster #%d: %s@runlevel %d\n",j,result_1->clusters_val[j].name,result_1->clusters_val[j].debuglevel);
        }
    }
    clnt_destroy( clnt );
}

as a result, we get some nice values on the clientside printed and of course no segfaults anymore on the serverside:

lars$ ./test_client localhost
I got 2 cluster structs in an array
cluster #0: cl1@runlevel 1
cluster #1: cl2@runlevel 2

sending a struct array with sun rpc from server to client

1 Answers1