Can't seem to get C TCP Server-Client Communications Right
- by Zeesponge
Ok i need some serious help here. I have to make a TCP Server Client. When the Client connects to server using a three stage handshake. AFterwards... while the Client is running in the terminal, the user enters linux shell commands like xinput list, ls -1, ect... something that uses standard output. The server accepts the commands and uses system() (in a fork() in an infinite loop) to run the commands and the standard output is redirected to the client, where the client prints out each line.
Afterward the server sends a completion signal of "\377\n". In which the client goes back to the command prompt asking for a new command and closes its connection and exit()'s when inputting "quit".
I know that you have to dup2() both the STDOUT_FILENO and STDERR_FILENO to the clients file descriptor {dup2(client_FD, STDOUT_FILENO). Everything works accept when it comes for the client to retrieve system()'s stdout and printing it out... all i get is a blank line with a blinking cursor (client waiting on stdin). I tried all kinds of different routes with no avail... If anyone can help out i would greatly appreciate it
TCP SERVER CODE
include
#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
//Prototype
void handle_client(int connect_fd);
int main()
{
int server_sockfd, client_sockfd;
socklen_t server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address;
server_sockfd = socket(AF_INET, SOCK_STREAM, 0);
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(9734);
server_len = sizeof(server_address);
bind(server_sockfd, (struct sockaddr *)&server_address, server_len);
/* Create a connection queue, ignore child exit details and wait for clients. */
listen(server_sockfd, 10);
signal(SIGCHLD, SIG_IGN);
while(1) {
printf("server waiting\n");
client_len = sizeof(client_address);
client_sockfd = accept(server_sockfd,
(struct sockaddr *)&client_address, &client_len);
if(fork() == 0)
handle_client(client_sockfd);
else
close(client_sockfd);
}
}
void handle_client(int connect_fd) {
const char* remsh = "<remsh>\n";
const char* ready = "<ready>\n";
const char* ok = "<ok>\n";
const char* command = "<command>\n";
const char* complete = "<\377\n";
const char* shared_secret = "<shapoopi>\n";
static char server_msg[201];
static char client_msg[201];
static char commands[201];
int sys_return;
//memset client_msg, server_msg, commands
memset(&client_msg, 0, sizeof(client_msg));
memset(&server_msg, 0, sizeof(client_msg));
memset(&commands, 0, sizeof(commands));
//read remsh from client
read(connect_fd, &client_msg, 200);
//check remsh validity from client
if(strcmp(client_msg, remsh) != 0) {
errno++;
perror("Error Establishing Handshake");
close(connect_fd);
exit(1);
}
//memset client_msg
memset(&client_msg, 0, sizeof(client_msg));
//write remsh to client
write(connect_fd, remsh, strlen(remsh));
//read shared_secret from client
read(connect_fd, &client_msg, 200);
//check shared_secret validity from client
if(strcmp(client_msg, shared_secret) != 0) {
errno++;
perror("Invalid Security Passphrase");
write(connect_fd, "no", 2);
close(connect_fd);
exit(1);
}
//memset client_msg
memset(&client_msg, 0, sizeof(client_msg));
//write ok to client
write(connect_fd, ok, strlen(ok));
// dup2 STDOUT_FILENO <= client fd, STDERR_FILENO <= client fd
dup2(connect_fd, STDOUT_FILENO);
dup2(connect_fd, STDERR_FILENO);
//begin while... while read (client_msg) from server and >0
while(read(connect_fd, &client_msg, 200) > 0) {
//check command validity from client
if(strcmp(client_msg, command) != 0) {
errno++;
perror("Error, unable to retrieve data");
close(connect_fd);
exit(1);
}
//memset client_msg
memset(&client_msg, 0, sizeof(client_msg));
//write ready to client
write(connect_fd, ready, strlen(ready));
//read commands from client
read(connect_fd, &commands, 200);
//run commands using system( )
sys_return = system(commands);
//check success of system( )
if(sys_return < 0) {
perror("Invalid Commands");
errno++;
}
//memset commands
memset(commands, 0, sizeof(commands));
//write complete to client
write(connect_fd, complete, sizeof(complete));
}
}
TCP CLIENT CODE
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include "readline.c"
int main(int argc, char *argv[])
{
int sockfd;
int len;
struct sockaddr_in address;
int result;
const char* remsh = "<remsh>\n";
const char* ready = "<ready>\n";
const char* ok = "<ok>\n";
const char* command = "<command>\n";
const char* complete = "<\377\n";
const char* shared_secret = "<shapoopi>\n";
static char server_msg[201];
static char client_msg[201];
memset(&client_msg, 0, sizeof(client_msg));
memset(&server_msg, 0, sizeof(server_msg));
/* Create a socket for the client. */
sockfd = socket(AF_INET, SOCK_STREAM, 0);
/* Name the socket, as agreed with the server. */
memset(&address, 0, sizeof(address));
address.sin_family = AF_INET;
address.sin_addr.s_addr = inet_addr(argv[1]);
address.sin_port = htons(9734);
len = sizeof(address);
/* Now connect our socket to the server's socket. */
result = connect(sockfd, (struct sockaddr *)&address, len);
if(result == -1) {
perror("ACCESS DENIED");
exit(1);
}
//write remsh to server
write(sockfd, remsh, strlen(remsh));
//read remsh from server
read(sockfd, &server_msg, 200);
//check remsh validity from server
if(strcmp(server_msg, remsh) != 0) {
errno++;
perror("Error Establishing Initial Handshake");
close(sockfd);
exit(1);
}
//memset server_msg
memset(&server_msg, 0, sizeof(server_msg));
//write shared secret text to server
write(sockfd, shared_secret, strlen(shared_secret));
//read ok from server
read(sockfd, &server_msg, 200);
//check ok velidity from server
if(strcmp(server_msg, ok) != 0 ) {
errno++;
perror("Incorrect security phrase");
close(sockfd);
exit(1);
}
//? dup2 STDIN_FILENO = server socket fd?
//dup2(sockfd, STDIN_FILENO);
//begin while(1)///////////////////////////////////////
while(1){
//memset both msg arrays
memset(&client_msg, 0, sizeof(client_msg));
memset(&server_msg, 0, sizeof(server_msg));
//print Enter Command, scan input, fflush to stdout
printf("<<Enter Command>> ");
scanf("%s", client_msg);
fflush(stdout);
//check quit input, if true close and exit successfully
if(strcmp(client_msg, "quit") == 0) {
printf("Exiting\n");
close(sockfd);
exit(EXIT_SUCCESS);
}
//write command to server
write(sockfd, command, strlen(command));
//read ready from server
read(sockfd, &server_msg, 200);
//check ready validity from server
if(strcmp(server_msg, ready) != 0) {
errno++;
perror("Failed Server Communications");
close(sockfd);
exit(1);
}
//memset server_msg
memset(&server_msg, 0, sizeof(server_msg));
//begin looping and retrieving from stdin,
//break loop at EOF or complete
while((read(sockfd, server_msg, 200) != 0) && (strcmp(server_msg, complete) != 0)) {
//while((fgets(server_msg, 4096, stdin) != EOF) || (strcmp(server_msg, complete) == 0)) {
printf("%s", server_msg);
memset(&server_msg, 0, sizeof(server_msg));
}
}
}
