IPC in Linux using Sockets and Signals
Signals
kill(gPid,SIGUSR1);//Server sends the SIGUSR1 signal to the client where gPid is the pid of the client
(void) signal(SIGUSR1, signal_callback);//Client receives the SIGUSR1 signal using signal_callback function
SOCKET
There are two types of SOCKETS AF_UNIX and AF_INET.AF_UNIX is used for inter process communication within the same system whereas in AF_INET server and client can be placed in different systems.If we use a loopback address 127.0.0.1 than AF_INET sockets can be used for IPC in the same system.
Following are the sample working code which demonstrates the use of sockets(AF_UNIX and AF_INET) for interprocess communication
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///////////////////////server_unix////////////////
/* a server in the unix domain. */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
#define SERVER_PATH "/tmp/server9"
void error(char *);
int main(int argc, char *argv[])
{
int sockfd, newsockfd, servlen, clilen, n;
struct sockaddr_un cli_addr, serv_addr;
char buf[81];
if ((sockfd = socket(AF_UNIX,SOCK_STREAM,0)) < 0)
error("creating socket");
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sun_family = AF_UNIX;
strcpy(serv_addr.sun_path, SERVER_PATH);
servlen=strlen(serv_addr.sun_path) +
sizeof(serv_addr.sun_family);
if(bind(sockfd,(struct sockaddr *)&serv_addr,SUN_LEN(&serv_addr)/*servlen*/)<0)
error("binding socket");
listen(sockfd,5);
clilen = sizeof(cli_addr);
newsockfd = accept(
sockfd,(struct sockaddr *)&cli_addr,&clilen);
if (newsockfd < 0)
error("accepting");
n=read(newsockfd,buf,80);
printf("Message from client:%s\n",buf);
printf("Enter your message: ");
bzero(buf,80);
fgets(buf,80,stdin);
write(newsockfd,buf,strlen(buf));
unlink( SERVER_PATH );
}
void error(char *msg)
{
perror(msg);
exit(0);
}
///////////////////////////////////////////////////
//////////////////////client_UNIX////////////////
/* a client in the unix domain */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdio.h>
void error(char *);
#define SERVER_PATH "/tmp/server9"
void main(int argc, char *argv[])
{
int sockfd, servlen,n;
struct sockaddr_un serv_addr;
char buffer[81];
bzero((char *)&serv_addr,sizeof(serv_addr));
serv_addr.sun_family = AF_UNIX;
strcpy(serv_addr.sun_path, SERVER_PATH);
servlen = strlen(serv_addr.sun_path) +
sizeof(serv_addr.sun_family);
if ((sockfd = socket(AF_UNIX, SOCK_STREAM,0)) < 0)
error("Creating socket");
if (connect(sockfd, (struct sockaddr *)
&serv_addr, servlen) < 0)
error("Connecting");
printf("Enter your message: ");
bzero(buffer,80);
fgets(buffer,80,stdin);
write(sockfd,buffer,strlen(buffer));
bzero(buffer,80);
n=read(sockfd,buffer,80);
printf("Message from server:%s\n",buffer);
unlink( SERVER_PATH );
}
void error(char *msg)
{
perror(msg);
exit(0);
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////server_inet/////////////////
/* server inet domain*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define PORT_NO 8999
void error(char *msg)
{
perror(msg);
exit(1);
}
int main()
{
int sockfd, newsockfd, portno, clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
bzero((char *) &serv_addr, sizeof(serv_addr));
portno = PORT_NO;
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
if (bind(sockfd, (struct sockaddr *) &serv_addr,
sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd,
(struct sockaddr *) &cli_addr,
&clilen);
if (newsockfd < 0)
error("ERROR on accept");
bzero(buffer,256);
n = read(newsockfd,buffer,255);
if (n < 0) error("ERROR reading from socket");
printf("Here is the message: %s\n",buffer);
n = write(newsockfd,"Server recieved the message",18);
if (n < 0) error("ERROR writing to socket");
return 0;
}
/////////////////////////////////////////////////////
/////////////////////////client_inet////////////////////
/* client in inet domain*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#define HOST_NAME "127.0.0.1"
#define PORT_NO 8999
void error(char *msg)
{
perror(msg);
exit(0);
}
int main()
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256] = {0};
portno = PORT_NO;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(HOST_NAME);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
printf("Enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
return 0;
}
////////////////////////////////////////////////////////
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