The following is an example of the lowest layer of RPC on the server side program:
#define RMTPROGNUM (u_long)0x3fffffffL
#define RMTPROGVER (u_long)0x1L
#define LONGPROC 1
#define STRINGPROC 2
#define MAXLEN 100
#include <stdio.h>
#include <rpc\rpc.h>
#include <sys\socket.h>
main(argc, argv)
int argc;
char *argv[ ];
{
int rmtprog();
SVCXPRT *transp;
...
/* create TCP transport handle */
transp = svctcp_create(RPC_ANYSOCK, 1024*10, 1024*10);
/* or create UDP transport handle */
/* transp = svcudp_create(RPC_ANYSOCK); */
if (transp == NULL) /* check transport handle creation */
{
fprintf(stderr, "can't create an RPC server transport\n");
exit(-1);
}
/* If exists, remove the mapping of remote program and port */
pmap_unset(RMTPROGNUM, RMTPROGVER);
/* register remote program (TCP transport) with local Portmapper */
if (!svc_register(transp, RMTPROGNUM, RMTPROGVER, rmtprog,
IPPROTO_TCP))
/* or register remote program (UDP transport) with local Portmapper */
/* if (!svc_register(transp, RMTPROGNUM, RMTPROGVER, rmtprog,*/
/* IPPROTO_UDP)) */
{
fprintf(stderr, "can't register rmtprog() service\n");
exit(-1);
}
svc_run();
printf("Error:svc_run should never reaches this point \n");
exit(1);
}
rmtprog(rqstp, transp) /* code for remote program */
struct svc_req *rqstp;
SVCXPRT *transp;
{
long in_long,out_long;
char buf[100], *in_string=buf, *out_string=buf;
...
switch((int)rqstp->rq_proc) /* Which procedure ? */
{
case NULLPROC:
if (!svc_sendreply(transp,xdr_void, 0))
{
fprintf(stderr,"can't reply to RPC call\n");
exit(-1);
}
return;
case LONGPROC:
...
/* Process the request */
if (!svc_sendreply(transp,xdr_long,&out_long))
{
fprintf(stderr,"can't reply to RPC call\n");
exit(-1);
}
return;
case STRINGPROC: /* send received "Hello" message back */
/* to client */
svc_getargs(transp,xdr_wrapstring,(char *)&in_string);
strcpy(out_string,in_string);
/* send a reply back to a RPC client */
if (!svc_sendreply(transp,xdr_wrapstring,
(char *)&out_string))
{
fprintf(stderr,"can't reply to RPC call\n");
exit(-1);
}
return;
case ... :
...
/* Any Remote procedure in RMTPROGNUM program */
...
default:
/* Requested procedure not found */
svcerr_noproc(transp);
return;
}
}
The following steps describe the lowest layer of RPC on the server side program:
The svctcp_create() and svcudp_create() calls create TCP and UDP transport handles (SVCXPRT) respectively, used for receiving and replying to RPC messages. The SVCXPRT transport handle structure is defined in the <RPC\SVC.H> header file.
If the argument of the svctcp_create() call is RPC_ANYSOCK, the RPC library creates a socket on which to receive and reply to remote procedure calls. The svctcp_create() and clnttcp_create() calls cause the RPC library calls to bind the appropriate socket, if it is not already bound.
If the argument of the svctcp_create() call is not RPC_ANYSOCK, the svctcp_create() call expects its argument to be a valid socket number. If you specify your own socket, it can be bound or unbound. If it is bound to a port by you, the port numbers of the svctcp_create() and clnttcp_create() calls must match.
If the send and receive buffer size parameter of svctcp_create() is 0, the system selects a reasonable default.
If the rmtprog service terminated abnormally the last time it was used, the pmap_unset() call erases any trace of it before restarting. The pmap_unset() call erases the entry for RMTPROGNUM from the Portmapper's table.
A service can register its port number with the local Portmapper service by specifying a nonzero protocol number in the svc_register() call. A programmer at the client machine can determine the server port number by consulting Portmapper at the server machine. You can do this automatically by specifying 0 as the port number in the clntudp_create() or clnttcp_create() calls.
Finally, the program and version number are associated with the rmtprog procedure. The final argument to the svc_register() call is the protocol being used, which in this case is IPPROTO_TCP. Register at the program level, not at the procedure level.
The rmtprog service routine must call and dispatch the appropriate XDR calls based on the procedure number. Unlike the registerrpc() call, which performs them automatically, the rmtprog routine requires two tasks:
The user service (rmtprog) serializes the results and returns them to the RPC caller through the svc_sendreply() call.
Parameters of the svc_sendreply() call include the: