We will create a RPC (Remote Procedure Calling) program with C which is something advance than 'Hello World'. But it is still simple to understand. In a program like 'Hello World' we cannot learn how to pass parameters or return a value using protocol definitions because those are not required for a simple printing program.
With this program administrator can store any kind of message or notice for other users in the network. Low level user can access to the admin's messages or notices with their client computers by calling to the server computer. Notices can be stored in a simple text file in .txt format. When client requests the service by passing its particular user name and password, server reads the particular text file and return text to the client. We will see step by step how we can develop our simple program.
1. Define the protocol :-
All our stuff should start with defining the protocol file or .x file.
struct credintials{
char uname[200];
char pwd[200];
};
program NOTICE_PROG{
version NOTICE_VERS{
string NOTICE(credintials)=1;
}=1;
}=0x33674131;
In the protocol file in RPC we have to define particular input parameters, return type, program name, version and a program number.
In RPC we have to organize all individual parameters in to one data structure and pass as input parameters. In this case we have defined two char arrays to pass user name and the password from the user.
First column of the ninth line defines the return type of the program. This program should return a string which will be read from a text file. Even though in C we don't have a data type called 'string' but a char array, IDL has the key word 'string' for set of characters.
In the third column of the ninth line we have included 'credintials' as a input parameter which we defined as a structure.
Then we have to save this file with .x extension. In this case I save this as notice.x
2. To simply create a RPC program, we need a external program called 'RPC gen' which can automatically generate header, stubs, Makefile and server, client code templates. If you are using ubuntu it is already installed in your system. If you are working with windows, you have to install it.(How ever I recommend you to use ubuntu environment for this task.)
Then you have to check whether all the required libraries are installed. If not you have to install them. To check the availability of those libraries with terminal
>rpcinfo
3. Then we have to run our note.x file with rpcgen and generate the above mentioned files. Just simply type below command in the linux terminal.
>rpcgen -a -C notice.x
Set of files will be genarated as mentioned below :-
Makefile.notice
notice.h
notice_client.c
notice_server.c
notice_clnt.c
notice_xdr.c
notice_svc.c
4. For the ease of commanding you can rename Makefile.notice to Makefile. Makefile includes set of terminal commands related to compiling our RPC program.
5. Then simply type in terminal as
>make
That will compile the program and generate another new set of files as mentioned below :-
notice_client.o
notice_server.o
notice_clnt.o
notice_xdr.o
notice_svc.o
notice_client
notice_server
6. Now you have successfully completed a sketch of a RPC program. Since notice_client and notice_server executable files are already generated, we can execute them by giving following terminal commands.
To start the server program
>sudo ./notice_server
Open another terminal window and run client program
>./notice_client localhost
You will be informed that the connection failed since we have not code the program yet. But already we have the auto generated basic structure of the client and server program as notice_client.c and notice_server.c
7. Now we will code the notice_client.c file as follows.
#include "notice.h"
void
notice_prog_1(char *host,char *uname,char *pwd)//changed get additional parameters username and password
{
CLIENT *clnt;
char * *result_1;
credintials notice_1_arg;
#ifndef DEBUG
clnt = clnt_create (host, NOTICE_PROG, NOTICE_VERS, "udp");
if (clnt == NULL) {
clnt_pcreateerror (host);
exit (1);
}
#endif /* DEBUG */
strcpy(notice_1_arg.uname, uname); //set the user name and passwords to the char pointers in the structure
strcpy(notice_1_arg.pwd, pwd); //set the user name and passwords to the char pointers in the structure
result_1 = notice_1(¬ice_1_arg, clnt); //pass the values to the notice_1() in notice_server.c
if (result_1 == (char **) NULL) {
clnt_perror (clnt, "call failed");
}else{
printf("Output is : %s\n",*result_1); //print the returned string from the notice_server.c
}
#ifndef DEBUG
clnt_destroy (clnt);
#endif /* DEBUG */
}
int
main (int argc, char *argv[])
{
char *host;
char *uname; //Defined char pointer
char *pwd; //Defined char pointer
if (argc < 2) {
printf ("usage: %s server_host\n", argv[0]);
exit (1);
}
host = argv[1];
uname=argv[2]; //get the username as a command line argument
pwd=argv[3]; //get the password as a command line argument
notice_prog_1 (host,uname,pwd); //pass all gathered variables to the notice_porog_1 method as parameters
exit (0);
}
8. Now we will change the notice_server.c file as follows
#include "notice.h"
#include <string.h>//Additional header file has been included since we uses string functions in our server program
char * getData1();
char * getData2();
char * getData3();
char * getData4();
char **
notice_1_svc(credintials *argp, struct svc_req *rqstp)
{
printf("Responses to the client");
static char * result;
//int authentication=100;
/*Program code for authentication process for 4 individual clients*/
int authenticUname;
int authenticPwd;
int authenticUname1;
int authenticPwd1;
int authenticUname2;
int authenticPwd2;
int authenticUname3;
int authenticPwd3;
authenticUname=strcmp(argp->uname,"udara");
authenticPwd=strcmp(argp->pwd,"123");
authenticUname1=strcmp(argp->uname,"nimal");
authenticPwd1=strcmp(argp->pwd,"456");
authenticUname2=strcmp(argp->uname,"sarath");
authenticPwd2=strcmp(argp->pwd,"789");
authenticUname3=strcmp(argp->uname,"kamal");
authenticPwd3=strcmp(argp->pwd,"147");
if(authenticUname==0 && authenticPwd==0){
result=getData1();
}else if(authenticUname1==0 && authenticPwd1==0){
result=getData2();
}else if(authenticUname2==0 && authenticPwd2==0){
result=getData3();
}else if(authenticUname3==0 && authenticPwd3==0){
result=getData4();
}else{
result="Unauthenticated";
}
return &result;
}
char * getData1(){
FILE *input;
input=fopen("notice1.txt","r");
char *text2;
char text[1000];
text2=fgets(text,999,input);
//strcpy(dest, src);
return text2;
}
char * getData2(){
FILE *input;
input=fopen("notice2.txt","r");
char *text2;
char text[1000];
text2=fgets(text,999,input);
//strcpy(dest, src);
return text2;
}
char * getData3(){
FILE *input;
input=fopen("notice3.txt","r");
char *text2;
char text[1000];
text2=fgets(text,999,input);
//strcpy(dest, src);
return text2;
}
char * getData4(){
FILE *input;
input=fopen("notice4.txt","r");
char *text2;
char text[1000];
text2=fgets(text,999,input);
//strcpy(dest, src);
return text2;
}
9. Now we are almost complete. You have to create notice1.txt, notice2.txt, notice3.txt, notice4.txt and include some text.
10. Run
make command again and run the client and server program.
Reference :-
http://www.cs.rutgers.edu/~pxk/rutgers/notes/rpc/
Source :- https://github.com/udaraseneviratnesmuc/Simple-RPC
