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.SH

\&\fBrpcgen\fP Programming Guide

.NH 0

\&The \fBrpcgen\fP Protocol Compiler

.IX rpcgen "" \fIrpcgen\fP "" PAGE MAJOR

.LP

.IX RPC "" "" \fIrpcgen\fP

The details of programming applications to use Remote Procedure Calls

can be overwhelming.  Perhaps most daunting is the writing of the XDR

routines necessary to convert procedure arguments and results into

their network format and vice-versa.

.LP

Fortunately,

.I rpcgen(1)

exists to help programmers write RPC applications simply and directly.

.I rpcgen

does most of the dirty work, allowing programmers to debug

the  main  features of their application, instead of requiring them to

spend most of their time debugging their network interface code.

.LP

.I rpcgen

is a  compiler.  It accepts a remote program interface definition written

in a language, called RPC Language, which is similar to C.  It produces a C

language output which includes stub versions of the client routines, a

server skeleton, XDR filter routines for both parameters and results, and a

header file that contains common definitions. The client stubs interface

with the RPC library and effectively hide the network from their callers.

The server stub similarly hides the network from the server procedures that

are to be invoked by remote clients.

.I rpcgen 's

output files can be compiled and linked in the usual way.  The developer

writes server procedures\(emin any language that observes Sun calling

conventions\(emand links them with the server skeleton produced by

.I rpcgen

to get an executable server program.  To use a remote program, a programmer

writes an ordinary main program that makes local procedure calls to the

client stubs produced by

.I rpcgen .

Linking this program with

.I rpcgen 's

stubs creates an executable program.  (At present the main program must be

written in C).

.I rpcgen

options can be used to suppress stub generation and to specify the transport

to be used by the server stub.

.LP

Like all compilers,

.I rpcgen

reduces development time

that would otherwise be spent coding and debugging low-level routines.

All compilers, including

.I rpcgen ,

do this at a small cost in efficiency

and flexibility.  However,   many compilers allow  escape  hatches for

programmers to  mix low-level code with  high-level code.

.I rpcgen

is no exception.  In speed-critical applications, hand-written routines

can be linked with the

.I rpcgen

output without any difficulty.  Also, one may proceed by using

.I rpcgen

output as a starting point, and then rewriting it as necessary.

(If you need a discussion of RPC programming without

.I rpcgen ,

see the

.I "Remote Procedure Call Programming Guide)\.

.NH 1

\&Converting Local Procedures into Remote Procedures

.IX rpcgen "local procedures" \fIrpcgen\fP

.IX rpcgen "remote procedures" \fIrpcgen\fP

.LP

Assume an application that runs on a single machine, one which we want

to convert to run over the network.  Here we will demonstrate such a

conversion by way of a simple example\(ema program that prints a

message to the console:

.ie t .DS

.el .DS L

.ft I

/*

 * printmsg.c: print a message on the console

 */

.ft CW

#include 

main(argc, argv)

        int argc;

        char *argv[];

{

        char *message;

        if (argc < 2) {

                fprintf(stderr, "usage: %s \en", argv[0]);

                exit(1);

        }

        message = argv[1];

        if (!printmessage(message)) {

                fprintf(stderr, "%s: couldn't print your message\en",

                        argv[0]);

                exit(1);

        }

        printf("Message Delivered!\en");

        exit(0);

}

.ft I

/*

 * Print a message to the console.

 * Return a boolean indicating whether the message was actually printed.

 */

.ft CW

printmessage(msg)

        char *msg;

{

        FILE *f;

        f = fopen("/dev/console", "w");

        if (f == NULL) {

                return (0);

        }

        fprintf(f, "%s\en", msg);

        fclose(f);

        return(1);

}

.DE

.LP

And then, of course:

.ie t .DS

.el .DS L

.ft CW

example%  \fBcc printmsg.c -o printmsg\fP

example%  \fBprintmsg "Hello, there."\fP

Message delivered!

example%

.DE

.LP

If

.I printmessage()

was turned into  a remote procedure,

then it could be  called from anywhere in   the network.

Ideally,  one would just  like to stick   a  keyword like

.I remote

in  front  of a

procedure to turn it into a  remote procedure.  Unfortunately,

we  have to live  within the  constraints of  the   C language, since

it existed   long before  RPC did.  But   even without language

support, it's not very difficult to make a procedure remote.

.LP

In  general, it's necessary to figure  out  what the types are for

all procedure inputs and outputs.  In  this case,   we  have a

procedure

.I printmessage()

which takes a  string as input, and returns  an integer

as output.  Knowing  this, we can write a  protocol specification in RPC

language that  describes the remote  version of

.I printmessage ().

Here it is:

.ie t .DS

.el .DS L

.ft I

/*

 * msg.x: Remote message printing protocol

 */

.ft CW

program MESSAGEPROG {

        version MESSAGEVERS {

                int PRINTMESSAGE(string) = 1;

        } = 1;

} = 99;

.DE

.LP

Remote procedures are part of remote programs, so we actually declared

an  entire  remote program  here  which contains  the single procedure

.I PRINTMESSAGE .

This procedure was declared to be  in version  1 of the

remote program.  No null procedure (procedure 0) is necessary because

.I rpcgen

generates it automatically.

.LP

Notice that everything is declared with all capital  letters.  This is

not required, but is a good convention to follow.

.LP

Notice also that the argument type is \*Qstring\*U and not \*Qchar *\*U.  This

is because a \*Qchar *\*U in C is ambiguous.  Programmers usually intend it

to mean  a null-terminated string   of characters, but  it  could also

represent a pointer to a single character or a  pointer to an array of

characters.  In  RPC language,  a  null-terminated  string is

unambiguously called a \*Qstring\*U.

.LP

There are  just two more things to  write.  First, there is the remote

procedure itself.  Here's the definition of a remote procedure

to implement the

.I PRINTMESSAGE

procedure we declared above:

.ie t .DS

.el .DS L

.vs 11

.ft I

/*

 * msg_proc.c: implementation of the remote procedure "printmessage"

 */

.ft CW

#include 

#include     /* \fIalways needed\fP  */

#include "msg.h"        /* \fIneed this too: msg.h will be generated by rpcgen\fP */

.ft I

/*

 * Remote verson of "printmessage"

 */

.ft CW

int *

printmessage_1(msg)

        char **msg;

{

        static int result;  /* \fImust be static!\fP */

        FILE *f;

        f = fopen("/dev/console", "w");

        if (f == NULL) {

                result = 0;

                return (&result);

        }

        fprintf(f, "%s\en", *msg);

        fclose(f);

        result = 1;

        return (&result);

}

.vs

.DE

.LP

Notice here that the declaration of the remote procedure

.I printmessage_1()

differs from that of the local procedure

.I printmessage()

in three ways:

.IP  1.

It takes a pointer to a string instead of a string itself.  This

is true of all  remote procedures:  they always take pointers to  their

arguments rather than the arguments themselves.

.IP  2.

It returns a pointer to an  integer instead of  an integer itself. This is

also generally true of remote procedures: they always return a pointer

to their results.

.IP  3.

It has an \*Q_1\*U appended to its name.  In general, all remote

procedures called by

.I rpcgen

are named by  the following rule: the name in the program  definition

(here

.I PRINTMESSAGE )

is converted   to all

lower-case letters, an underbar (\*Q_\*U) is appended to it, and

finally the version number (here 1) is appended.

.LP

The last thing to do is declare the main client program that will call

the remote procedure. Here it is:

.ie t .DS

.el .DS L

.ft I

/*

 * rprintmsg.c: remote version of "printmsg.c"

 */

.ft CW

#include 

#include      /* \fIalways needed\fP  */

#include "msg.h"         /* \fIneed this too: msg.h will be generated by rpcgen\fP */

main(argc, argv)

        int argc;

        char *argv[];

{

        CLIENT *cl;

        int *result;

        char *server;

        char *message;

        if (argc < 3) {

                fprintf(stderr, "usage: %s host message\en", argv[0]);

                exit(1);

        }

.ft I

        /*

         * Save values of command line arguments

         */

.ft CW

        server = argv[1];

        message = argv[2];

.ft I

        /*

         * Create client "handle" used for calling \fIMESSAGEPROG\fP on the

         * server designated on the command line. We tell the RPC package

         * to use the "tcp" protocol when contacting the server.

         */

.ft CW

        cl = clnt_create(server, MESSAGEPROG, MESSAGEVERS, "tcp");

        if (cl == NULL) {

.ft I

                /*

                 * Couldn't establish connection with server.

                 * Print error message and die.

                 */

.ft CW

                clnt_pcreateerror(server);

                exit(1);

        }

.ft I

        /*

         * Call the remote procedure "printmessage" on the server

         */

.ft CW

        result = printmessage_1(&message, cl);

        if (result == NULL) {

.ft I

                /*

                 * An error occurred while calling the server.

                 * Print error message and die.

                 */

.ft CW

                clnt_perror(cl, server);

                exit(1);

        }

.ft I

        /*

         * Okay, we successfully called the remote procedure.

         */

.ft CW

        if (*result == 0) {

.ft I

                /*

                 * Server was unable to print our message.

                 * Print error message and die.

                 */

.ft CW

                fprintf(stderr, "%s: %s couldn't print your message\en",

                        argv[0], server);

                exit(1);

        }

.ft I

        /*

         * The message got printed on the server's console

         */

.ft CW

        printf("Message delivered to %s!\en", server);

}

.DE

There are two things to note here:

.IP  1.

.IX "client handle, used by rpcgen" "" "client handle, used by \fIrpcgen\fP"

First a client \*Qhandle\*U is created using the RPC library routine

.I clnt_create ().

This client handle will be passed  to the stub routines

which call the remote procedure.

.IP  2.

The remote procedure

.I printmessage_1()

is called exactly  the same way as it is  declared in

.I msg_proc.c

except for the inserted client handle as the first argument.

.LP

Here's how to put all of the pieces together:

.ie t .DS

.el .DS L

.ft CW

example%  \fBrpcgen msg.x\fP

example%  \fBcc rprintmsg.c msg_clnt.c -o rprintmsg\fP

example%  \fBcc msg_proc.c msg_svc.c -o msg_server\fP

.DE

Two programs were compiled here: the client program

.I rprintmsg

and the server  program

.I msg_server .

Before doing this  though,

.I rpcgen

was used to fill in the missing pieces.

.LP

Here is what

.I rpcgen

did with the input file

.I msg.x :

.IP  1.

It created a header file called

.I msg.h

that contained

.I #define 's

for

.I MESSAGEPROG ,

.I MESSAGEVERS

and

.I PRINTMESSAGE

for use in  the  other modules.

.IP  2.

It created client \*Qstub\*U routines in the

.I msg_clnt.c

file.   In this case there is only one, the

.I printmessage_1()

that was referred to from the

.I printmsg

client program.  The name  of the output file for

client stub routines is always formed in this way:  if the name of the

input file is

.I FOO.x ,

the   client  stubs   output file is    called

.I FOO_clnt.c .

.IP  3.

It created  the  server   program which calls

.I printmessage_1()

in

.I msg_proc.c .

This server program is named

.I msg_svc.c .

The rule for naming the server output file is similar  to the

previous one:  for an input  file   called

.I FOO.x ,

the   output   server   file is  named

.I FOO_svc.c .

.LP

Now we're ready to have some fun.  First, copy the server to a

remote machine and run it.  For this  example,  the

machine is called \*Qmoon\*U.  Server processes are run in the

background, because they never exit.

.ie t .DS

.el .DS L

.ft CW

moon% \fBmsg_server &\fP

.DE

Then on our local machine (\*Qsun\*U) we can print a message on \*Qmoon\*Us

console.

.ie t .DS

.el .DS L

.ft CW

sun% \fBprintmsg moon "Hello, moon."\fP

.DE

The message will get printed to \*Qmoon\*Us console.  You can print a

message on anybody's console (including your own) with this program if

you are able to copy the server to their machine and run it.

.NH 1

\&Generating XDR Routines

.IX RPC "generating XDR routines"

.LP

The previous example  only demonstrated  the  automatic generation of

client  and server RPC  code.

.I rpcgen

may also  be used to generate XDR routines, that  is,  the routines

necessary to  convert   local  data

structures into network format and vice-versa.  This example presents

a complete RPC service\(ema remote directory listing service, which uses

.I rpcgen

not  only  to generate stub routines, but also to  generate  the XDR

routines.  Here is the protocol description file:

.ie t .DS

.el .DS L

.ft I

/*

 * dir.x: Remote directory listing protocol

 */

.ft CW

const MAXNAMELEN = 255;         /* \fImaximum length of a directory entry\fP */

typedef string nametype;        /* \fIa directory entry\fP */

typedef struct namenode *namelist;              /* \fIa link in the listing\fP */

.ft I

/*

 * A node in the directory listing

 */

.ft CW

struct namenode {

        nametype name;          /* \fIname of directory entry\fP */

        namelist next;          /* \fInext entry\fP */

};

.ft I

/*

 * The result of a READDIR operation.

 */

.ft CW

union readdir_res switch (int errno) {

case 0:

        namelist list;  /* \fIno error: return directory listing\fP */

default:

        void;           /* \fIerror occurred: nothing else to return\fP */

};

.ft I

/*

 * The directory program definition

 */

.ft CW

program DIRPROG {

        version DIRVERS {

                readdir_res

                READDIR(nametype) = 1;

        } = 1;

} = 76;

.DE

.SH

Note:

.I

Types (like

.I readdir_res

in the example above) can be defined using

the \*Qstruct\*U, \*Qunion\*U and \*Qenum\*U keywords, but those keywords

should not be used in subsequent declarations of variables of those types.

For example, if you define a union \*Qfoo\*U, you should declare using

only \*Qfoo\*U and not \*Qunion foo\*U.  In fact,

.I rpcgen

compiles

RPC unions into C structures and it is an error to declare them using the

\*Qunion\*U keyword.

.LP

Running

.I rpcgen

on

.I dir.x

creates four output files.  Three are the same as before: header file,

client stub routines and server skeleton.  The fourth are the XDR routines

necessary for converting the data types we declared into XDR format and

vice-versa.  These are output in the file

.I dir_xdr.c .

.LP

Here is the implementation of the

.I READDIR

procedure.

.ie t .DS

.el .DS L

.vs 11

.ft I

/*

 * dir_proc.c: remote readdir implementation

 */

.ft CW

#include 

#include 

#include "dir.h"

extern int errno;

extern char *malloc();

extern char *strdup();

readdir_res *

readdir_1(dirname)

        nametype *dirname;

{

        DIR *dirp;

        struct direct *d;

        namelist nl;

        namelist *nlp;

        static readdir_res res; /* \fImust be static\fP! */

.ft I

        /*

         * Open directory

         */

.ft CW

        dirp = opendir(*dirname);

        if (dirp == NULL) {

                res.errno = errno;

                return (&res);

        }

.ft I

        /*

         * Free previous result

         */

.ft CW

        xdr_free(xdr_readdir_res, &res);

.ft I

        /*

         * Collect directory entries.

         * Memory allocated here will be freed by \fIxdr_free\fP

         * next time \fIreaddir_1\fP is called

         */

.ft CW

        nlp = &res.readdir_res_u.list;

        while (d = readdir(dirp)) {

                nl = *nlp = (namenode *) malloc(sizeof(namenode));

                nl->name = strdup(d->d_name);

                nlp = &nl->next;

        }

        *nlp = NULL;

.ft I

        /*

         * Return the result

         */

.ft CW

        res.errno = 0;

        closedir(dirp);

        return (&res);

}

.vs

.DE

Finally, there is the client side program to call the server:

.ie t .DS

.el .DS L

.ft I

/*

 * rls.c: Remote directory listing client

 */

.ft CW

#include 

#include        /* \fIalways need this\fP */

#include "dir.h"                /* \fIwill be generated by rpcgen\fI */

extern int errno;

main(argc, argv)

        int argc;

        char *argv[];

{

        CLIENT *cl;

        char *server;

        char *dir;

        readdir_res *result;

        namelist nl;

        if (argc != 3) {

                fprintf(stderr, "usage: %s host directory\en",

                  argv[0]);

                exit(1);

        }

.ft I

        /*

         * Remember what our command line arguments refer to

         */

.ft CW

        server = argv[1];

        dir = argv[2];

.ft I

        /*

         * Create client "handle" used for calling \fIMESSAGEPROG\fP on the

         * server designated on the command line. We tell the RPC package

         * to use the "tcp" protocol when contacting the server.

         */

.ft CW

        cl = clnt_create(server, DIRPROG, DIRVERS, "tcp");

        if (cl == NULL) {

.ft I

                /*

                 * Couldn't establish connection with server.

                 * Print error message and die.

                 */

.ft CW

                clnt_pcreateerror(server);

                exit(1);

        }

.ft I

        /*

         * Call the remote procedure \fIreaddir\fP on the server

         */

.ft CW

        result = readdir_1(&dir, cl);

        if (result == NULL) {

.ft I

                /*

                 * An error occurred while calling the server.

                 * Print error message and die.

                 */

.ft CW

                clnt_perror(cl, server);

                exit(1);

        }

.ft I

        /*

         * Okay, we successfully called the remote procedure.

         */

.ft CW

        if (result->errno != 0) {

.ft I

                /*

                 * A remote system error occurred.

                 * Print error message and die.

                 */

.ft CW

                errno = result->errno;

                perror(dir);

                exit(1);

        }

.ft I

        /*

         * Successfully got a directory listing.

         * Print it out.

         */

.ft CW

        for (nl = result->readdir_res_u.list; nl != NULL;

          nl = nl->next) {

                printf("%s\en", nl->name);

        }

        exit(0);

}

.DE

Compile everything, and run.

.DS

.ft CW

sun%  \fBrpcgen dir.x\fP

sun%  \fBcc rls.c dir_clnt.c dir_xdr.c -o rls\fP

sun%  \fBcc dir_svc.c dir_proc.c dir_xdr.c -o dir_svc\fP

sun%  \fBdir_svc &\fP

moon%  \fBrls sun /usr/pub\fP

\&.

\&..

ascii

eqnchar

greek

kbd

marg8

tabclr

tabs

tabs4

moon%

.DE

.LP

.IX "debugging with rpcgen" "" "debugging with \fIrpcgen\fP"

A final note about

.I rpcgen :

The client program and the server procedure can be tested together

as a single program by simply linking them with each other rather

than with the client and server stubs.  The procedure calls will be

executed as ordinary local procedure calls and the program can be

debugged with a local debugger such as

.I dbx .

When the program is working, the client program can be linked to

the client stub produced by

.I rpcgen

and the server procedures can be linked to the server stub produced

by

.I rpcgen .

.SH

.I NOTE :

\fIIf you do this, you may want to comment out calls to RPC library

routines, and have client-side routines call server routines

directly.\fP

.LP

.NH 1

\&The C-Preprocessor

.IX rpcgen "C-preprocessor" \fIrpcgen\fP

.LP

The C-preprocessor is  run on all input  files before they are

compiled, so all the preprocessor directives are legal within a \*Q.x\*U

file. Four symbols may be defined, depending upon which output file is

getting generated. The symbols are:

.TS

box tab (&);

lfI lfI

lfL l .

Symbol&Usage

_

RPC_HDR&for header-file output

RPC_XDR&for XDR routine output

RPC_SVC&for server-skeleton output

RPC_CLNT&for client stub output

.TE

.LP

Also,

.I rpcgen

does  a little preprocessing   of its own. Any  line that

begins  with  a percent sign is passed  directly into the output file,

without any interpretation of the line.  Here is a simple example that

demonstrates the preprocessing features.

.ie t .DS

.el .DS L

.ft I

/*

 * time.x: Remote time protocol

 */

.ft CW

program TIMEPROG {

        version TIMEVERS {

                unsigned int TIMEGET(void) = 1;

        } = 1;

} = 44;

#ifdef RPC_SVC

%int *

%timeget_1()

%{

%        static int thetime;

%

%        thetime = time(0);

%        return (&thetime);

%}

#endif

.DE

The '%' feature is not generally recommended, as there is no guarantee

that the compiler will stick the output where you intended.

.NH 1

\&\fBrpcgen\fP Programming Notes

.IX rpcgen "other operations" \fIrpcgen\fP

.sp

.NH 2

\&Timeout Changes

.IX rpcgen "timeout changes" \fIrpcgen\fP

.LP

RPC sets a default timeout of 25 seconds for RPC calls when

.I clnt_create()

is used.  This timeout may be changed using

.I clnt_control()

Here is a small code fragment to demonstrate use of

.I clnt_control ():

.ID

struct timeval tv;

CLIENT *cl;

.sp .5

cl = clnt_create("somehost", SOMEPROG, SOMEVERS, "tcp");

if (cl == NULL) {

        exit(1);

}

tv.tv_sec = 60; /* \fIchange timeout to 1 minute\fP */

tv.tv_usec = 0;

clnt_control(cl, CLSET_TIMEOUT, &tv);

.DE

.NH 2

\&Handling Broadcast on the Server Side

.IX "broadcast RPC"

.IX rpcgen "broadcast RPC" \fIrpcgen\fP

.LP

When a procedure is known to be called via broadcast RPC,

it is usually wise for the server to not reply unless it can provide

some useful information to the client.  This prevents the network

from getting flooded by useless replies.

.LP

To prevent the server from replying, a remote procedure can

return NULL as its result, and the server code generated by

.I rpcgen

will detect this and not send out a reply.

.LP

Here is an example of a procedure that replies only if it

thinks it is an NFS server:

.ID

void *

reply_if_nfsserver()

{

        char notnull;   /* \fIjust here so we can use its address\fP */

.sp .5

        if (access("/etc/exports", F_OK) < 0) {

                return (NULL);  /* \fIprevent RPC from replying\fP */

        }

.ft I

        /*

         * return non-null pointer so RPC will send out a reply

         */

.ft L

        return ((void *)¬null);

}

.DE

Note that if procedure returns type \*Qvoid *\*U, they must return a non-NULL

pointer if they want RPC to reply for them.

.NH 2

\&Other Information Passed to Server Procedures

.LP

Server procedures will often want to know more about an RPC call

than just its arguments.  For example, getting authentication information

is important to procedures that want to implement some level of security.

This extra information is actually supplied to the server procedure as a

second argument.  Here is an example to demonstrate its use.  What we've

done here is rewrite the previous

.I printmessage_1()

procedure to only allow root users to print a message to the console.

.ID

int *

printmessage_1(msg, rq)

        char **msg;

        struct svc_req  *rq;

{

        static in result;       /* \fIMust be static\fP */

        FILE *f;

        struct suthunix_parms *aup;

.sp .5

        aup = (struct authunix_parms *)rq->rq_clntcred;

        if (aup->aup_uid != 0) {

                result = 0;

                return (&result);

        }

.sp

.ft I

        /*

         * Same code as before.

         */

.ft L

}

.DE

.NH 1

\&RPC Language

.IX RPCL

.IX rpcgen "RPC Language" \fIrpcgen\fP

.LP

RPC language is an extension of XDR  language.   The sole extension is

the addition of the

.I program

type.  For a complete description of the XDR language syntax, see the

.I "External Data Representation Standard: Protocol Specification"

chapter.  For a description of the RPC extensions to the XDR language,

see the

.I "Remote Procedure Calls: Protocol Specification"

chapter.

.LP

However, XDR language is so close to C that if you know C, you know most

of it already.  We describe here  the syntax of the RPC language,

showing a  few examples along the way.   We also show how  the various

RPC and XDR type definitions get  compiled into C  type definitions in

the output header file.

.KS

.NH 2

Definitions

\&

.IX rpcgen definitions \fIrpcgen\fP