RPC学习笔记

在查看libc6-dev软件包提供的工具（用 dpkg -L libc6-dev 命令）的时候，发现此软件包提供了一个有用的工具rpcgen命令。
通过rpcgen的man手册看到此工具的作用是把RPC源程序编译成C语言源程序，从而轻松实现远程过程调用。
下面的例子程序的作用是客户端程序取中心服务器上时间的，编程过程如下：
先编写一个 “ RPC 语言 ” ( RPC Language ( Remote Procedure Call Language ) ) 的源文件 test.x ，文件后缀名为 x 。
源代码如下：
program TESTPROG {
   version VERSION {
     string TEST(string) = 1;
   } = 1;
} = 87654321;说明：这里数字87654321是RPC程序编号，还有VERSION版本号为1，都是给RPC服务程序用的。同时指定程序接受一个字符串参数。

运行这个命令：
rpcgen test.x将生成三个源文件：
test_clnt.c  test.h  test_svc.c源文件test_clnt.c 内容如下：
/*
 * Please do not edit this file.
 * It was generated using rpcgen.
 */

#include <memory.h> /* for memset */
#include "test.h"

/* Default timeout can be changed using clnt_control() */
static struct timeval TIMEOUT = { 25, 0 };

char **
test_1(char **argp, CLIENT *clnt)
{
        static char *clnt_res;

        memset((char *)&clnt_res, 0, sizeof(clnt_res));
        if (clnt_call (clnt, TEST,
                (xdrproc_t) xdr_wrapstring, (caddr_t) argp,
                (xdrproc_t) xdr_wrapstring, (caddr_t) &clnt_res,
                TIMEOUT) != RPC_SUCCESS) {
                return (NULL);
        }
        return (&clnt_res);
}说明：这是一个客户端调用函数，即客户端代码需要用到此函数。

源文件test.h内容如下：
/*
 * Please do not edit this file.
 * It was generated using rpcgen.
 */

#ifndef _TEST_H_RPCGEN
#define _TEST_H_RPCGEN

#include <rpc/rpc.h>


#ifdef __cplusplus
extern "C" {
#endif


#define TESTPROG 87654321
#define VERSION 1

#if defined(__STDC__) || defined(__cplusplus)
#define TEST 1
extern  char ** test_1(char **, CLIENT *);
extern  char ** test_1_svc(char **, struct svc_req *);
extern int testprog_1_freeresult (SVCXPRT *, xdrproc_t, caddr_t);

#else /* K&R C */
#define TEST 1
extern  char ** test_1();
extern  char ** test_1_svc();
extern int testprog_1_freeresult ();
#endif /* K&R C */

#ifdef __cplusplus
}
#endif

#endif /* !_TEST_H_RPCGEN */说明：这里定义了一些公用头文件。

源文件test_svc.c内容如下：
/*
 * Please do not edit this file.
 * It was generated using rpcgen.
 */

#include "test.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

static void
testprog_1(struct svc_req *rqstp, register SVCXPRT *transp)
{
        union {
                char *test_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 TEST:
                _xdr_argument = (xdrproc_t) xdr_wrapstring;
                _xdr_result = (xdrproc_t) xdr_wrapstring;
                local = (char *(*)(char *, struct svc_req *)) test_1_svc;
                break;

        default:
                svcerr_noproc (transp);
                return;
        }
        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;
}

int
main (int argc, char **argv)
{
        register SVCXPRT *transp;

        pmap_unset (TESTPROG, VERSION);

        transp = svcudp_create(RPC_ANYSOCK);
        if (transp == NULL) {
                fprintf (stderr, "%s", "cannot create udp service.");
                exit(1);
        }
        if (!svc_register(transp, TESTPROG, VERSION, testprog_1, IPPROTO_UDP)) {
                fprintf (stderr, "%s", "unable to register (TESTPROG, VERSION, udp).");
                exit(1);
        }

        transp = svctcp_create(RPC_ANYSOCK, 0, 0);
        if (transp == NULL) {
                fprintf (stderr, "%s", "cannot create tcp service.");
                exit(1);
        }
        if (!svc_register(transp, TESTPROG, VERSION, testprog_1, IPPROTO_TCP)) {
                fprintf (stderr, "%s", "unable to register (TESTPROG, VERSION, tcp).");
                exit(1);
        }

        svc_run ();
        fprintf (stderr, "%s", "svc_run returned");
        exit (1);
        /* NOTREACHED */
}说明：这是一个标准的服务器端代码。

运行下列命令生成一个客户端源文件test_client.c：
rpcgen -Sc -o test_client.c test.x源代码test_client.c如下：
/*
 * This is sample code generated by rpcgen.
 * These are only templates and you can use them
 * as a guideline for developing your own functions.
 */

#include "test.h"


void
testprog_1(char *host)
{
        CLIENT *clnt;
        char * *result_1;
        char * test_1_arg;

#ifndef DEBUG
        clnt = clnt_create (host, TESTPROG, VERSION, "udp");
        if (clnt == NULL) {
                clnt_pcreateerror (host);
                exit (1);
        }
#endif  /* DEBUG */

        result_1 = test_1(&test_1_arg, clnt);
        if (result_1 == (char **) NULL) {
                clnt_perror (clnt, "call failed");
        }
#ifndef DEBUG
        clnt_destroy (clnt);
#endif   /* DEBUG */
}


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

        if (argc < 2) {
                printf ("usage: %s server_host\n", argv[0]);
                exit (1);
        }
        host = argv[1];
        testprog_1 (host);
exit (0);
}运行这个命令生成服务端源文件test_srv_func.c：
rpcgen -Ss -o test_srv_func.c test.x源文件test_srv_func.c内容如下：
/*
 * This is sample code generated by rpcgen.
 * These are only templates and you can use them
 * as a guideline for developing your own functions.
 */

#include "test.h"

char **
test_1_svc(char **argp, struct svc_req *rqstp)
{
        static char * result;

        /*
         * insert server code here
         */

        return &result;
}说明：这是一个服务器端调用的函数。

至此，我们就可以编译生成程序来运行了。
用下面的命令编译生成服务端程序test_server：
gcc -Wall -o test_server test_clnt.c test_srv_func.c test_svc.c用下面的命令编译生成客户端程序test_client：
gcc -Wall -o test_client test_client.c test_clnt.c 运行下列命令启动服务端：
./test_server运行下列命令可以进行客户端测试：
./test_client 127.0.0.1但是由于现的的服务端没有处理客户端请求，所以这样的程序还不能完成任何工作。

下面我们先给服务端程序加上代码，使这个服务器能完成一定的工作。即修改 test_srv_func.c ，在 “ * insert server code here ” 后面加上取时间的代码，即修改后的 test_srv_func.c 代码如下：
/*
 * This is sample code generated by rpcgen.
 * These are only templates and you can use them
 * as a guideline for developing your own functions.
 */
#include <time.h>
#include "test.h"

char **
test_1_svc(char **argp, struct svc_req *rqstp)
{
        static char * result;
        static char tmp_char[128];
        time_t rawtime;

        /*
         * insert server code here
         */
        if( time(&rawtime) == ((time_t)-1) ) {
                strcpy(tmp_char, "Error");
                result = tmp_char;
                return &result;
        }
        sprintf(tmp_char, "服务器当前时间是 :%s", ctime(&rawtime));
        result = tmp_char;

        return &result;
}再修改客户端代码以显示服务器端返回的内容，即修改test_client.c源文件，只需要修改其中的函数testprog_1，修改后如下：
void
testprog_1(char *host)
{
        CLIENT *clnt;
        char * *result_1;
        char * test_1_arg;

        test_1_arg = (char *)malloc(128);
#ifndef DEBUG
        clnt = clnt_create (host, TESTPROG, VERSION, "udp");
        if (clnt == NULL) {
                clnt_pcreateerror (host);
                exit (1);
        }
#endif  /* DEBUG */

        result_1 = test_1(&test_1_arg, clnt);
        if (result_1 == (char **) NULL) {
                clnt_perror (clnt, "call failed");
        }
        if (strcmp(*result_1, "Error") == 0) {
                fprintf(stderr, "%s: could not get the time\n", host);
                exit(1);
        }
        printf("收到消息 ... %s\n", *result_1);
#ifndef DEBUG
        clnt_destroy (clnt);
#endif   /* DEBUG */
}重新运行上述编译命令编译生成程序：
gcc -Wall -o test_server test_clnt.c test_srv_func.c test_svc.c
gcc -Wall -o test_client test_client.c test_clnt.c 启动服务端程序后运行客户端程序如下：
./test_client 127.0.0.1
收到消息 ... 服务器当前时间是 :Tue Feb 27 11:45:21 2007
为了省略每次输入gcc命令的麻烦，也为了维护我们的工程，可以运行下列命令生成一个Makefile文件：
rpcgen -Sm test.x > Makefile生成的Makefile内容如下：
# This is a template Makefile generated by rpcgen

# Parameters

CLIENT = test_client
SERVER = test_server

SOURCES_CLNT.c = 
SOURCES_CLNT.h = 
SOURCES_SVC.c = 
SOURCES_SVC.h = 
SOURCES.x = test.x

TARGETS_SVC.c =       
TARGETS_CLNT.c =       
TARGETS =            

OBJECTS_CLNT = $(SOURCES_CLNT.c:%.c=%.o) $(TARGETS_CLNT.c:%.c=%.o)
OBJECTS_SVC = $(SOURCES_SVC.c:%.c=%.o) $(TARGETS_SVC.c:%.c=%.o)
# Compiler flags 

CFLAGS += -g 
LDLIBS += -lnsl
RPCGENFLAGS = 

# Targets 

all : $(CLIENT) $(SERVER)

$(TARGETS) : $(SOURCES.x) 
        rpcgen $(RPCGENFLAGS) $(SOURCES.x)

$(OBJECTS_CLNT) : $(SOURCES_CLNT.c) $(SOURCES_CLNT.h) $(TARGETS_CLNT.c) 

$(OBJECTS_SVC) : $(SOURCES_SVC.c) $(SOURCES_SVC.h) $(TARGETS_SVC.c) 

$(CLIENT) : $(OBJECTS_CLNT) 
        $(LINK.c) -o $(CLIENT) $(OBJECTS_CLNT) $(LDLIBS) 

$(SERVER) : $(OBJECTS_SVC) 
        $(LINK.c) -o $(SERVER) $(OBJECTS_SVC) $(LDLIBS)

 clean:
         $(RM) core $(TARGETS) $(OBJECTS_CLNT) $(OBJECTS_SVC) $(CLIENT) $(SERVER)由于我们手工生成了源文件，所以要修改一下这个Makefile，修改后如下：
# This is a template Makefile generated by rpcgen

# Parameters

CLIENT = test_client
SERVER = test_server

SOURCES_CLNT.c = 
SOURCES_CLNT.h = 
SOURCES_SVC.c = 
SOURCES_SVC.h = 
SOURCES.x = test.x

TARGETS_SVC.c = test_clnt.c test_srv_func.c test_svc.c
TARGETS_CLNT.c = test_clnt.c test_client.c 
TARGETS = test.h   test_clnt.c test_svc.c    

OBJECTS_CLNT = $(SOURCES_CLNT.c:%.c=%.o) $(TARGETS_CLNT.c:%.c=%.o)
OBJECTS_SVC = $(SOURCES_SVC.c:%.c=%.o) $(TARGETS_SVC.c:%.c=%.o)
# Compiler flags 

CFLAGS += -g 
LDLIBS += -lnsl
RPCGENFLAGS = 

# Targets 

all : $(CLIENT) $(SERVER)

$(TARGETS) : $(SOURCES.x) 
        rpcgen $(RPCGENFLAGS) $(SOURCES.x)

$(OBJECTS_CLNT) : $(SOURCES_CLNT.c) $(SOURCES_CLNT.h) $(TARGETS_CLNT.c) 

$(OBJECTS_SVC) : $(SOURCES_SVC.c) $(SOURCES_SVC.h) $(TARGETS_SVC.c) 

$(CLIENT) : $(OBJECTS_CLNT) 
        $(LINK.c) -o $(CLIENT) $(OBJECTS_CLNT) $(LDLIBS) 

$(SERVER) : $(OBJECTS_SVC) 
        $(LINK.c) -o $(SERVER) $(OBJECTS_SVC) $(LDLIBS)

clean:
        $(RM) core $(TARGETS) $(OBJECTS_CLNT) $(OBJECTS_SVC) $(CLIENT) $(SERVER) *~