backlog-test.c

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


int main(int argc, const char *argv[]) {
	if (argc != 2) {
		const char *progname = (argc) ? argv[0] : "backlog-test";
		fprintf(stderr, "Usage: %s <backlog>\n", progname);
		return 1;
	}
	int backlog = atoi(argv[1]);
	fprintf(stderr, "Using backlog of %d\n", backlog);

	struct protoent *tcp_protent = getprotobyname("tcp");
	assert(tcp_protent);
	int sockfd = socket(AF_INET, SOCK_STREAM, tcp_protent->p_proto);
	if (sockfd == -1) {
		fprintf(stderr, "Failed to create socket: %s\n", strerror(errno));
		return 1;
	}
	fprintf(stderr, "Created socket %d\n", sockfd);

	if (listen(sockfd, backlog)) {
		fprintf(stderr, "Failed to listen on socket: %s\n", strerror(errno));
		return 1;
	}

	struct sockaddr_in sockaddr;
	socklen_t socklen = sizeof(sockaddr);
	assert(!getsockname(sockfd, (struct sockaddr *)&sockaddr, &socklen));
	fprintf(stderr, "Listening on all interfaces port %d\n", ntohs(sockaddr.sin_port));

	struct sockaddr_in sockaddr_remote;
	socklen_t socklen_remote = sizeof(sockaddr_remote);
	int connfd;
	while ((connfd = accept(sockfd, (struct sockaddr *)&sockaddr_remote, &socklen_remote)) != -1) {
		fprintf(stderr, "Accepted connection from %s:%d\n", inet_ntoa(sockaddr_remote.sin_addr), ntohs(sockaddr_remote.sin_port));
		fputs("Closing connection\n", stderr);
		assert(!close(connfd));
	}

	fprintf(stderr, "Failed to accept connection on socket: %s\n", strerror(errno));
	assert(!close(sockfd));

	return 0;
}