firewall-knocker/client/client.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <arpa/inet.h>

#include "config.h"

int
main(void)
{
	int sockfd;
	struct addrinfo hints;
	struct addrinfo *servinfo;
	struct addrinfo *p;
	int rv;
	int connected;

	// Set the hints
	memset(&hints, 0, sizeof hints);
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;

	// Get address info (AKA resolv hostname)
	if ((rv = getaddrinfo(SERVER_ADDRESS, PORT, &hints, &servinfo)) != 0)
	{
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
		return 1;
	}

	// Cycle OUTER
	while (1)
	{
		int con;

		// Here we assume that we are not connected.
		connected = 0;

		printf("Connecting...\n");

		// Create a socket
		for (p = servinfo; p != NULL; p = p->ai_next)
		{
			if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1)
			{
				perror("client: socket");
				continue;
			}

			break;
		}

		// If p is NULL, we didn't succeed to create a socket. This should never happen
		if (p == NULL)
		{
			fprintf(stderr, "client: failed to connect\n");
			return 2;
		}

		// Set the socket to non-blocking so we can control the timeout value
		fcntl(sockfd, F_SETFL, O_NONBLOCK);

		// Start the connection (it usually won't succeed yet)
		con = connect(sockfd, p->ai_addr, p->ai_addrlen);

		// If connect() returned an error saying the connection is in progress
		if ((con < 0) && (errno == EINPROGRESS))
		{
			// Cycle INNER1
			while (1)
			{
				struct timeval tv;
				int t;
				fd_set master;

				// Create an empty descriptor set, and add our socket to it
				FD_ZERO(&master);
				FD_SET(sockfd, &master);

				// Set the timeout value to SENDING_FREQ seconds
				tv.tv_sec = SENDING_FREQ;
				tv.tv_usec = 0;
				
				// Run the select()
				t = select(sockfd + 1, NULL, &master, NULL, &tv);

				if ((t < 0) && (errno != EINTR))
				{
					// Some serious error happened, let's exit
					perror("select");
					exit(1);
				}
				else if (t < 0)
				{
					// select() was interrupted, lets restart the INNER1 cycle
					printf("select() interrupted, continue\n");
					continue;
				}
				else if (t > 0)
				{
					size_t lon;
					int valopt;

	  				lon = sizeof(int); 
		  			if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, (void*)(&valopt), &lon) < 0)
				       	{
						fprintf(stderr, "Error in getsockopt() %d - %s\n", errno, strerror(errno)); 
						connected = 0;
						sleep(SENDING_FREQ);
						break;
					} 
					// Check the value returned... 
					if (valopt)
				       	{
						fprintf(stderr, "Error in delayed connection() %d - %s\n", valopt, strerror(valopt)); 
						connected = 0;
						sleep(SENDING_FREQ);
						break;
					}
					printf("Connected with select().\n");
					connected = 1;
					break;
				}
				else if (t == 0)
				{
					// Connection timed out, let's break out from INNER1
					printf("connect() timed out.\n");
					connected = 0;
					close(sockfd);
					break;
				}
			}
		}
		else if (con < 0)
		{
			// connect() error. Wait SENDING_FREQ seconds and try again (restarting the OUTER cycle)
			// XXX error handling?
			printf("connect() error, retry\n");
			sleep(SENDING_FREQ);
			connected = 0;
			continue;
		}
		else if (con == 0)
		{
			// We are now connected. Usually we won't get here, but in the select() loop above instead
			printf("Connected without select().\n");
			connected = 1;
		}

		if (connected)
		{
			// If we are connected, let's jump in the INNER2 cycle
			while (1)
			{
				fd_set read_fds;
				int t;
				struct timeval tv;
				char buf[MAXDATASIZE];

				// Create and empty descriptor set and add our socket
				FD_ZERO(&read_fds);
				FD_SET(sockfd, &read_fds);

				// Set the timeout value to SENDING_FREQ seconds
				tv.tv_sec = SENDING_FREQ;
				tv.tv_usec = 0;
				
				// Let's run the select()
				t = select(sockfd + 1, &read_fds, NULL, NULL, &tv);

				if ((t < 0) && (errno != EINTR))
				{
					// select() ran into an error, this is bad. Let's exit
					perror("select");
					exit(1);
				}
				else if (t < 0)
				{
					// select() interrupted, try again by restarting the INNER2 cycle
					printf("select() interrupted\n");
					continue;
				}
				else if (t > 0)
				{
					// We got some data from the server
					size_t len;

					printf("Data from server.\n");

					len = recv(sockfd, &buf, MAXDATASIZE, 0);

					if (len <= 0)
					{
						// If the received data length is at most 0, we are disconnected, so break out from INNER2
						printf("Closing connection.\n");
						connected = 0;
						close(sockfd);
						break;
					}
				}

				// If we arrive here, select() ran into timeout, so we should send some data to the server.
				printf("Sending data to server\n");
				send(sockfd, "!\n", 2, 0);
			}
		}
	}

	// This should never happen, but if so, let's clean up after ourselved
	freeaddrinfo(servinfo);

	close(sockfd);

	return 0;
}