#define _POSIX_C_SOURCE 200809L
#include <arpa/inet.h>
#include <errno.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

static int connect_local(unsigned short port)
{
	struct sockaddr_in address;
	int fd = socket(AF_INET, SOCK_STREAM, 0);
	if (fd < 0) return -1;
	memset(&address, 0, sizeof(address));
	address.sin_family = AF_INET;
	address.sin_port = htons(port);
	address.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	if (connect(fd, (struct sockaddr *)&address, sizeof(address))) {
		close(fd);
		return -1;
	}
	return fd;
}

static int send_all(int fd, const char *data, size_t length)
{
	while (length) {
		ssize_t sent = send(fd, data, length, 0);
		if (sent < 0 && errno == EINTR) continue;
		if (sent <= 0) return -1;
		data += sent;
		length -= (size_t)sent;
	}
	return 0;
}

static int request_page(unsigned short port, const char *url)
{
	const char *key = "abcdef1234567890";
	char request[4096], buffer[4096];
	int fd, n;
	int length = snprintf(request, sizeof(request),
		"<cmd='auth' msg='%s' '>\n<cmd='open_url' url='%s' '>", key, url);
	if (length < 0 || (size_t)length >= sizeof(request)) return -1;
	fd = connect_local(port);
	if (fd < 0) return -1;
	if (send_all(fd, request, (size_t)length) || shutdown(fd, SHUT_WR)) {
		close(fd);
		return -1;
	}
	while ((n = (int)recv(fd, buffer, sizeof(buffer), 0)) > 0) {
		if (fwrite(buffer, 1, (size_t)n, stdout) != (size_t)n) {
			close(fd);
			return -1;
		}
	}
	close(fd);
	if (n < 0) return -1;
	return fflush(stdout) ? -1 : 0;
}

int main(int argc, char **argv)
{
	struct sockaddr_in address;
	socklen_t address_length = sizeof(address);
	unsigned short port;
	int listener;
	pid_t child;
	int status, fd;
	if (argc != 3) {
		fprintf(stderr, "usage: %s DPI-HELPER URL\n", argv[0]);
		return 2;
	}
	listener = socket(AF_INET, SOCK_STREAM, 0);
	if (listener < 0) { perror("socket"); return 1; }
	memset(&address, 0, sizeof(address));
	address.sin_family = AF_INET;
	address.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	address.sin_port = 0;
	if (bind(listener, (struct sockaddr *)&address, sizeof(address)) ||
	    listen(listener, 8) || getsockname(listener, (struct sockaddr *)&address, &address_length)) {
		perror("bind/listen"); close(listener); return 1;
	}
	port = ntohs(address.sin_port);
	child = fork();
	if (child < 0) { perror("fork"); close(listener); return 1; }
	if (!child) {
		if (dup2(listener, STDIN_FILENO) < 0) _exit(126);
		close(listener);
		execl(argv[1], argv[1], (char *)NULL);
		perror("exec"); _exit(127);
	}
	close(listener);
	if (request_page(port, argv[2])) {
		perror("request page");
		kill(child, SIGTERM);
		waitpid(child, NULL, 0);
		return 1;
	}
	fd = connect_local(port);
	{
		const char *bye = "<cmd='auth' msg='abcdef1234567890' '>\n<cmd='DpiBye' '>";
		if (fd < 0 || send_all(fd, bye, strlen(bye))) {
		perror("send DpiBye");
		kill(child, SIGTERM);
		waitpid(child, NULL, 0);
		return 1;
		}
	}
	shutdown(fd, SHUT_WR);
	close(fd);
	if (waitpid(child, &status, 0) < 0) { perror("waitpid"); return 1; }
	return WIFEXITED(status) ? WEXITSTATUS(status) : 1;
}