Unix-domain socket server

unix-domain-echo-server.cpp

// File: socket-echo-server.cpp 
// Desc: Simple socket server with a single thread. 

#include <iostream>
#include <string> 
#include <vector>
#include <cassert> 
#include <cstring>  // memcpy 

// ----- Unix/Linux headers -----// 
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>    
#include <sys/socket.h>
#include <sys/un.h>

// -------------  MAIN() ------------------------------//

int main(int argc, char** argv)
{
	std::puts(" [INFO] Program started. ");
	const char* unix_sock_file = "/tmp/unix-socket-file";

	// --- Create socket file descriptor -----------------------//

	int sockfd = socket (  AF_UNIX, SOCK_STREAM, 0);
	assert( sockfd != - 1);

	struct sockaddr_un sa; 
	sa.sun_family = AF_UNIX; 
	strcpy( sa.sun_path, unix_sock_file);	

	// Remove file if it exists.	
	unlink(unix_sock_file);

	// ----- Bind to unix domain socket and wait for client connections ---------//
	if( ::bind(sockfd, (sockaddr *) &sa, sizeof(sa)) == -1)
	{
		int err = errno; 
		fprintf(stderr, "Error: unable to bind socket \n");
		fprintf(stderr, " [ERROR] => %s", strerror(err));
		return EXIT_FAILURE;
	}

	// Enables binding to the same address 
	int enable_reuseaddr = 1;
	if ( setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &enable_reuseaddr, sizeof(int)) < 0 )
	{
		fprintf(stderr, "Error: unable to set socket option. \n");
		return EXIT_FAILURE;
	}


	fprintf(stderr, " [TRACE] Listening client connection \n");

	int backlog = 5;
	assert( listen(sockfd, backlog) != -1 );

	// --------------- Server Main Loop --------------------------//

	// Infinite loop where client connections are handled
	while(true)
	{	
		/* [[ ============== BEGIN client loop =========== ]] */

		struct sockaddr_un client_sa; 
		socklen_t addrlen = sizeof(sockaddr_un); 

		fprintf(stderr, " [TRACE] Waiting for client connection. \n");
		int sock_client = accept(sockfd, (sockaddr *) &client_sa, &addrlen );
		
		if(sock_client == -1)
		{
			fprintf(stderr, " Error: failure to handle client socket. Check errno \n");
			close(sock_client);
			continue;
		}
	 	const char* welcome_msg = "\n => [INFO] Hello world client side!! \n";		
		
		// Send buffer content to client socket 
		send(sock_client, welcome_msg, strlen(welcome_msg), 0);

		char buffer[300];

		while(true){
			// Read message from client socket 
			ssize_t n = recv(sock_client, &buffer, 300, 0);
			if(n == 0){ break; }

			std::fprintf(stdout, " [INFO] Received: ");			
			::write(STDOUT_FILENO, buffer, n);

			// Send content back 
			send(sock_client, buffer, n, 0);

			// Compare 4 first bytes of buffer and 'quit' 
			if( strncmp(buffer, "quit", 4) == 0)
			{
				fprintf(stderr, " [TRACE] Shutdown connection. Ok. \n");
				// Close client connection 
				shutdown(sock_client, SHUT_RDWR);
				close(sock_client);
				break;
			}			
		}
	
	} /* [[ ============== END client loop =========== ]] */

	// Release resource => RAII (Resource-Acquisition-Is-Initialization) fits here. 
	close(sockfd);

	return 0;
}