linux rpc

Linux RPC

Comer Chapter 21(RPCgen Concept)

RFC 1057 – RPC Spec.UNIX Network Programming - Stevens

1

Sockets API Limitations

• Must explicitly account for differences in systems– Byte order (big-endian / little-endian)

• Limited to sending characters (without tricking the system)– requires source and destination to implicitly

understand the data transformation.

2

Client / Server Between SystemsOne Solution:

• eXternal Data Representation (XDR)

• Developed by Sun Microsystems

• A standard for representing data over the network.

• Includes a set of library routines for converting data between local format and XDR format (either direction).

3

XDR Data Types• int 32 bits• unsigned int 32 bits• bool 32 bits• enum arbitrary• hyper 64 bits• unsigned hyper 64 bits• float 32 bits• double 64 bits• opaque arbitrary

• String arbitrary• fixed array arbitrary• counted array arbitrary• structure arbitrary• discriminated union arbitrary.• void 0• symbolic constant arbitrary• optional data arbitrary

4

XDR Data Conversion

• Objective:– Gather all parameter data into a buffer in XDR

format

• Procedure:– Create a buffer (xdrmem_create)

5

XDR Data Conversion

• Objective:– Gather all parameter data into a buffer in XDR

format

• Procedure:– Create a buffer (xdrmem_create)

6

#include <rpc/xdr.h>#define BUFSIZE 4000

...XDR * xdrs;char buf[BUFSIZE];xdrmen_create(xdrs, buf, BUFSIZE, XDR_ENCODE);

XDR Data Conversion Routines

xdr_bool (xdrs, ptrBool);

xdr_bytes (xdrs,str,strSize,maxsize);

xdr_char (xdrs, ptrChar);

xdr_double(xdrs, prtDouble);

xdr_enum(xdrs, ptrInt);

xdr_float(xdrs, ptrFloat);

xdr_int (xdrs, ptrInt);

xdr_long (xdrs, ptrLong);

xdr_opaque (xdrs, ptrChar, count);

xdr_pointer (xdrs, ptrObj, pbjSize, xdrObj);

xdrs_short (xdrs, ptrShort);

xdrs_u_char (xdrs, ptrUchar);

xdrs_u_int (xdrs, ptrUint);

xdrs_u_long (xdrs, ptrUlong);

xdrs_u_short (xdrs, ptrUshort);

xdr_union (xdrs, ptrDiscrim, ptrUnion, choiceFcn, default);

xdr_vector (xdrs, ptrArray, size, elemSize, elemProc);

xdr_void ( );

7

XDR Data Conversion

– Add data items in order to the buffer (after converting to XDR format)

8

int myInt;...myInt = 260;xdr_int(xdrs, &myInt);

RPC Programming MechanismsONC (Open Network Computing)

• XDR library routines for data conversion• XDR library routines for complex data

structures• RPC run-time library routines• Program generator tool

9

RPC Programming Process

• Dividing the program into local and remote procedures.

10

Proc A

Client Stub

Server Stub

Proc B

RPC

RPC Dispatching(Procedure Location)

11

Proc A1

Client Stub

Server Stub

Proc B1

Proc A2

Client StubProc B2

Server Stub

Dispatcher

RPC

RPC

RPC Interface Specification

12

Proc A

Client comm

Server Iface

Proc B

Server Comm

Client Iface

RPC

RPCgen Input and Output

• Input– Q.x Interface specification file

• Output– Q.h Declarations header file– Q_xdr.cpp XDR procedure calls used to

marshal arguments– Q_clnt.cpp Client-side communications stub– Q_svc.cpp Server-side communications stub

13

RPC Process Flow

14

Q.x rpcgen

Q_clnt.cpp

Q.h

Q_xdr.cpp

Q_svc.cpp

Clientapplication

Clientinterface

Serverinterface

Remoteprocedures

Server

Clientcompile

compile

RPC General Build Procedure

15

Develop Interface

Develop Client Develop Server

Developing the Interface

16

MyApp.x

RPCgen

MyApp_clnt.cClient Stub

MyApp_svc.cServer Stub

MyApp.h

MyApp_xdr.c

Developing the Server

17

MyApp.x

RPCgen

MyApp_svc.cServer Stub

MyApp.hMySrvr.c MyApp_xdr.c

C Compiler

Linker

MySrvr.exe

Developing the Client

18

MyApp.x

RPCgen

MyApp_clnt.cClient Stub

MyApp.hMyClnt.c

C Compiler

Linker

MyClnt.exe

MyApp_xdr.c

How the Server Prepares for a Connection

• (Be certain that Portmap is running)• Create UDP service• Register UDP service with Portmap• Create TCP service• Register TCP service with Portmap• Run service...– Uses select( ) to monitor ports.

19

Start Portmap

Portmap is included in all Linux distributions as a standard server.

Under Red Hat / Fedora Open services applet , select portmap and startFrom command line (as root)

/sbin/service portmap start

Other distributions should be similar

20

Server concurrency mode

RPC servers can be created in either single threaded or multi-threaded mode.

Servers automatically create and (when done) destroy a thread for each incoming connection.

21

Register the Server Program

svc_register(port#, SERV#, VER#, serv_func, proto#);

port#: port on which the service is activeSERV#: unique number for the serviceVER#: version for this particular serviceserv_func: name by which this function is calledproto#: IPPROTO_UDP or IPPROTO_TCP

22

How the Client Establishes a Connection

• Make a Remote Procedure Call• Find the Server Host Computer• Find Server Process Port # (through Portmap)• Create a (connection) to the Server Process

23

How the Client Establishes a Connection

clnt_create(server, SERV#, VER#, proto#);

remote procedure call...

Clnt_destroy(CLIENT);

24

Example #1

• Temperature Server (Fahrenheit to Centigrade)– Parameters passed as integers– TCP / IP port connection

• Source files:– temp.x– Tclient.c– tempServer.c

25

temp.x

program TEMPSERV {version TEMPVERS {

int TempConv(int) = 1; //procedure number} = 1; //version number

} = 77; //program number

26

TClient.c#include <stdio.h>, <stdlib.h>, <string.h>#include <rpc/rpc.h>#include "temp.h"#define YES 0#define NO 1

void main (int argc, char *argv[]){

int tempconvert(int temp, char *srvr);int temperature, nuTemp;int loopFlag;char srvr[25];CLIENT * cl;

27

TClient.c (cont)

strcpy (srvr, argv[1]);cl = clnt_create(srvr, TEMPSERV, TEMPVERS, "tcp");loopFlag = YES;

while(loopFlag == YES){

printf("Enter temperature in Faherenheit (-999 to quit)");

scanf ("%d", &temperature);ans = tempconv_1(&temperature, cl);

28

TClient.c (cont)

if (ans != NULL)nuTemp = * ans;

if (temperature == -999 || temperature == -9999)

{loopFlag = NO;printf ("Goodbye...\n");continue;

}printf("That’s %2d in centigrade\n", nuTemp);

}clnt_destroy(cl);return 0;

}

29

tempServer.c

#include <stdlib.h>, <unistd.h>, <stdio.h>#include <rpc/rpc.h>, "temp.h"

static int count;static int nuTemp;

int *tempconv_1_svc (int *val, struct svc_req * rqst)

{int oldTemp;oldTemp = *val;

30

tempServer.c

if (oldTemp == -9999){

printf("We're shutting down...\n");exit (0);

}printf("We got a temperature of %d, ", oldTemp);count++;nuTemp = (int)((5*(oldTemp -32)) / 9.0);printf("and we returned a value of %d\n", nuTemp);sleep(1);return (&nuTemp);

}

31

Files created with rpcgen

• Input:– temp.x

• Output– temp.h– temp_xdr.c (NULL file)– temp_clnt.c– temp_svc.c

32

temp.h#include <rpc/rpc.h>

#ifdef __cplusplus

extern "C" {

#endif

#define TEMPSERV 77

#define TEMPVERS 1

#if defined(__STDC__) || defined(__cplusplus)

#define TempConv 1

extern int * tempconv_1(int *, CLIENT *);

extern int * tempconv_1_svc(int *, struct svc_req *);

extern int tempserv_1_freeresult (SVCXPRT *, xdrproc_t, caddr_t);

#ifdef __cplusplus}

#endif

#endif /* !_TEMP_H_RPCGEN */

33

temp_xdr.c

#include <rpc/rpc.h>

#include "temp.h"

34

temp_clnt.c#include <memory.h> /* for memset */#include "temp.h“/* Default timeout can be changed using

clnt_control() */

static struct timeval TIMEOUT = { 25, 0 };

int *tempconv_1(int *argp, CLIENT *clnt){static int clnt_res;memset((char *)&clnt_res, 0, sizeof(clnt_res));

35

temp_clnt.c (cont)

if (clnt_call (clnt, TempConv,(xdrproc_t) xdr_int, (caddr_t)

argp, (xdrproc_t) xdr_int, (caddr_t) &clnt_res,TIMEOUT) != RPC_SUCCESS)

{return (NULL);

}return (&clnt_res);}

36

temp_svc.c

#include "temp.h“#include <stdio.h>#include <stdlib.h>#include <rpc/pmap_clnt.h>#include <string.h>#include <memory.h>#include <sys/socket.h>#include <netinet/in.h>

#ifndef SIG_PF#define SIG_PF void(*)(int)#endif

37

temp_svc.c (cont)static void tempserv_1(struct svc_req *rqstp, register SVCXPRT *transp){

union {

int tempconv_1_arg;

} argument;

char *result;

xdrproc_t _xdr_argument, _xdr_result;

char *(*local)(char *, struct svc_req *);

switch (rqstp->rq_proc) {

case NULLPROC:

(void) svc_sendreply (transp, (xdrproc_t) xdr_void, (char *)NULL);return;

case TempConv:

_xdr_argument = (xdrproc_t) xdr_int;

_xdr_result = (xdrproc_t) xdr_int;

local = (char *(*)(char *, struct svc_req *)) tempconv_1_svc;break;

default:

svcerr_noproc (transp);

return; } 38

temp_svc.c (cont)memset ((char *)&argument, 0, sizeof (argument));if (!svc_getargs (transp, (xdrproc_t) _xdr_argument,

(caddr_t) &argument)) {svcerr_decode (transp);return;

}result = (*local)((char *)&argument, rqstp);if (result != NULL && !svc_sendreply(transp, (xdrproc_t) _xdr_result, result)) {

svcerr_systemerr (transp);}if (!svc_freeargs (transp, (xdrproc_t) _xdr_argument, (caddr_t) &argument)) {

fprintf (stderr, "%s", "unable to free arguments");exit (1);

}return;

}

39

temp_svc.c (cont)int main (int argc, char **argv){

register SVCXPRT *transp;pmap_unset (TEMPSERV, TEMPVERS);transp = svcudp_create(RPC_ANYSOCK);if (transp == NULL) {

fprintf (stderr, "%s", "can’t create udp service."); exit(1);}if (!svc_register(transp, TEMPSERV, TEMPVERS,

tempserv_1, IPPROTO_UDP)) {fprintf (stderr, "%s", "unable to register

(TEMPSERV, TEMPVERS, udp).");exit(1);

}

40

temp_svc.c (cont)transp = svctcp_create(RPC_ANYSOCK, 0, 0);

if (transp == NULL) {fprintf (stderr, "%s", "cannot create

tcp service.");

exit(1);}if (!svc_register(transp, TEMPSERV, TEMPVERS,

tempserv_1, IPPROTO_TCP)) {fprintf (stderr, "%s", "unable to

register (TEMPSERV, TEMPVERS, tcp).");

exit(1);}svc_run ();fprintf (stderr, "%s", "svc_run returned");exit (1); /* NOTREACHED */}

41

Sample Client Output

D:\data\RPC\onrpc_temp\client\Debug>client localhost

Enter the temperature in Faherenheit (-999 to quit)32

That would be 0 in centigrade

Enter the temperature in Faherenheit (-999 to quit)100

That would be 37 in centigrade

Enter the temperature in Faherenheit (-999 to quit)212

That would be 100 in centigrade

Enter the temperature in Faherenheit (-999 to quit)-9999

Goodbye...

D:\data\RPC\onrpc_temp\client\Debug>

42

Sample Server Output

D:\data\RPC\examples\onrpc_temp\server\Debug>server

We got a temperature of 32, and we returned a value of 0

We got a temperature of 100, and we returned a value of 37

We got a temperature of 212, and we returned a value of 100

We're shutting down...

D:\data\RPC\examples\onrpc_temp\server\Debug>

43

Summary

• Linux RPC Implementation models SUN ONCRPC functionality

• RPC specific programming limited to linking original applications code with rpcgen interface code.

44