Linux下C语言编程的 RPC远程调用编程

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) *~