// Jeremy M. Rifkin 11.25.19
// Demonstrate that EAGAIN/EWOULDBLOCK can be triggered on accept(2) by a recv timeout
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>

void fail(char* format) {
	fprintf(stderr, format, errno);
	fflush(stderr);
	exit(1);
}

int main (int argc, char *argv[]) {
	int err;
	int socketfd = socket(AF_INET, SOCK_STREAM, 0);
	if(socketfd < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to create socket (errno: %d)... This shouldn't have "
			"happened.\n");

	// Configure socket
	struct sockaddr_in server;
	server.sin_family = AF_INET;
	server.sin_port = htons(0); // port 0 for random port
	server.sin_addr.s_addr = htonl(INADDR_ANY);

	// Set reuseaddr
	int opt = 1;
	err = setsockopt(socketfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
	if(err < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to set socket reuseaddr (errno: %d)... This shouldn't "
			"have happened.\n");

	// Configure timeout
	struct timeval timeout;
	timeout.tv_sec = 4; // 4 second timeout
	timeout.tv_usec = 0;
	err = setsockopt(socketfd, SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout, sizeof timeout);
	if(err < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to set socket recv timeout (errno: %d)... This "
			"shouldn't have happened.\n");

	// Bind the socket
	err = bind(socketfd, (struct sockaddr*) &server, sizeof(server));
	if(err < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to bind socket (errno: %d)... This shouldn't have "
			"happened.\n");

	// Mark socket as passive.
	err = listen(socketfd, 128);
	if(err < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to listen on socket (errno: %d)... This shouldn't "
			"have happened.\n");

	// Get port
	// Serves as both a check and also accommodates for "random" ports.
	struct sockaddr_in addr;
	socklen_t addr_len = sizeof(addr);
	err = getsockname(socketfd, (struct sockaddr*)&addr, &addr_len);
	if(err < 0)
		fail("\x1b[1;35mError:\x1b[0m failed to get socket address (errno: %d)... This shouldn't "
			"have happened.\n");
	printf("Socket listening on port %d\n", ntohs(addr.sin_port));
	
	// Demonstrate recv timeout failure
	printf("\nA 4 second recv timeout has been set on the socket.\n");
	printf("The program will now attempt to accept connections.\n");
	printf("It should fail with error EAGAIN/EWOULDBLOCK roughly\n");
	printf("every 4 seconds.\n\n");
	while(1) {
		struct sockaddr_in client;
		socklen_t client_len = sizeof(client);
		int clientfd = accept(socketfd, (struct sockaddr*)&client, &client_len);

		if(clientfd < 0) {
			if(errno == EAGAIN)
				fprintf(stderr, "\x1b[1;35mError:\x1b[0m Socket failed to accept with error EAGAIN."
					"\n");
			else if(errno == EWOULDBLOCK)
				fprintf(stderr, "\x1b[1;35mError:\x1b[0m Socket failed to accept with error "
					"EWOULDBLOCK.\n");
			else
				fprintf(stderr, "\x1b[1;35mError:\x1b[0m failed to establish new connection "
					"(errno: %d)... This shouldn't have happened.\n",
					errno);
			fflush(stderr);
		}
	}

	return 0;
}