rpserver.c

/*
	Yang J. Ren
	rpserver: remote popen server
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/errno.h>
#include <sys/wait.h>
#include <string.h>
#include <unistd.h>
#define BUFSIZE 8096
void cm(int sockfd);

int main(int argc, char **argv)
{
	static char usage[] = "Usage: %s [-p port]\n";
	//Initialize port to 0 i.e. PPORT
	int port = 0;
	//Check for correct usage format
	if (argc == 3){
		if (strcmp(argv[1],"-p")==0){
			int intCheck;
			if (atoi(argv[2])!=0){
				port = atoi(argv[2]);
				printf("Port: %i\n",port);
			}
			else{
				fprintf(stderr, usage, argv[0]);
				exit(1);
			}
		}
		else{
			fprintf(stderr, usage, argv[0]);
			exit(1);
		}
	}
	else if (argc == 1){
		//parse PPORT into port
		char* envPort;
		envPort = getenv("PPORT");
		if (envPort == NULL){
			fprintf(stderr, "PPORT has not been set.\n");
			exit(1);
		}
		else{
			printf("Port: %s\n", envPort); 
			port = atoi(envPort);
		}
	}
	else{
		fprintf(stderr, usage, argv[0]);
		exit(1);
	}

	int listenfd, connfd, ret;
	socklen_t clilen;
	struct sockaddr_in cliaddr, servaddr;
	clilen = sizeof(cliaddr);
	listenfd = socket(AF_INET, SOCK_STREAM, 0);

	// Allows for socket reuse
	int on = 1;
	ret = setsockopt (listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));

	//Set up connections on the given port from all interfaces
	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl (INADDR_ANY);
	servaddr.sin_port = htons (port);

	//bind to the port
	if((ret=bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)))!=0){
		fprintf(stderr,"Bind error.\n");
	}

	//listen for incoming connections
	int maxConn = 8;
	if((ret=listen(listenfd, maxConn))!=0){
		fprintf(stderr, "Listen error.\n");
	}
	while (1){
		connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
		cm(connfd);
		close(connfd);
	}
}

void cm(int sockfd){
	//child process check
	switch (fork()){
			case -1:
			fprintf(stderr, "Fork failed!\n");
			default:
			close(sockfd);
			return;
			case 0:
			break;
		}
	//popen simulator
	char command[BUFSIZE];
	read(sockfd, command, BUFSIZE);
	shutdown(sockfd,SHUT_RD);
	close(0);
	close(1);
	dup2(sockfd, 1);
	execlp("/bin/sh", "/bin/sh", "-c", command, (char*)0);
	fprintf(stderr, "Unknown command: %s", command);
	exit(1);
}