// Copyright 2005 Ben Hutchings <ben@decadent.org.uk>.
// See the file "COPYING" for licence details.

#include "x_frame_buffer.hpp"

#include <cassert>
#include <cstdio>
#include <cstring>
#include <stdexcept>

#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/utsname.h>
#include <unistd.h>
#include <wait.h>

#include "auto_fd.hpp"
#include "auto_handle.hpp"
#include "temp_file.hpp"

namespace
{
    struct addrinfo_factory
    {
	addrinfo * operator()() const { return NULL; }
    };
    struct addrinfo_closer
    {
	void operator()(addrinfo * addr_list) const
	    {
		if (addr_list)
		    freeaddrinfo(addr_list);
	    }
    };
    typedef auto_handle<addrinfo *, addrinfo_closer, addrinfo_factory>
        auto_addrinfo;

    int select_display_num(auto_fd & tcp4_socket, auto_fd & tcp6_socket)
    {
	// Minimum and maximum display numbers to use.  Xvnc and ssh's
	// proxies start at 10, so we'll follow that convention.  We
	// have to put a limit on iteration somewhere, and 100
	// displays seems rather excessive so we'll stop there.
	const int min_display_num = 10;
	const int max_display_num = 99;

	for (int display_num = min_display_num;
	     display_num <= max_display_num;
	     ++display_num)
	{
	    // Check that there's no lock file for the local socket
	    // for this display.  We could also check for stale locks,
	    // but this will probably do.
	    char lock_file_name[20];
	    std::sprintf(lock_file_name, "/tmp/.X%d-lock", display_num);
	    if (!(access(lock_file_name, 0) == -1 && errno == ENOENT))
		continue;

	    // Attempt to create TCP socket(s) and bind them to the
	    // appropriate port number.  We won't set the X server to
	    // listen on a TCP socket but this does ensure that ssh
	    // isn't using and won't use this display number.  This is
	    // roughly based on the x11_create_display_inet function
	    // in OpenSSH.

	    auto_addrinfo addr_list;

	    {
		addrinfo hints = {};
		hints.ai_family = AF_UNSPEC;
		hints.ai_socktype = SOCK_STREAM;
		char port_str[5 + 1];
		std::sprintf(port_str, "%d", 6000 + display_num);
		addrinfo * addr_list_temp;
		int error = getaddrinfo(NULL, port_str, &hints,
					     &addr_list_temp);
		if (error != 0)
		    throw std::runtime_error(
			std::string("getaddrinfo: ")
			.append(gai_strerror(error)));
		addr_list.reset(addr_list_temp);
	    }

	    const addrinfo * addr;

	    for (addr = addr_list.get(); addr != NULL; addr = addr->ai_next)
	    {
		// We're only interested in TCPv4 and TCPv6.
		if (addr->ai_family != AF_INET && addr->ai_family != AF_INET6)
		    continue;
		auto_fd & tcp_socket =
		    (addr->ai_family == AF_INET) ? tcp4_socket : tcp6_socket;

		tcp_socket.reset(socket(addr->ai_family,
					SOCK_STREAM,
					addr->ai_protocol));
		if (tcp_socket.get() < 0)
		{
		    // If the family is unsupported, no-one can bind
		    // to this address, so this is not a problem.
		    if (errno == EAFNOSUPPORT
#		        ifdef EPFNOSUPPORT
		        || errno == EPFNOSUPPORT
#		        endif
			)
			continue;
		    throw std::runtime_error(
			std::string("socket: ").append(strerror(errno)));
		}

		// Don't let TCPv6 sockets interfere with TCPv4 sockets.
#		ifdef IPV6_V6ONLY
		if (addr->ai_family == AF_INET6)
		{
		    int on = 1;
		    if (setsockopt(tcp_socket.get(), IPPROTO_IPV6, IPV6_V6ONLY,
				   &on, sizeof(on)) != 0)
		    {
			throw std::runtime_error(
			    std::string("setsockopt IPV6_V6ONLY: ")
			    .append(strerror(errno)));
		    }
		}
#		endif

		if (bind(tcp_socket.get(), addr->ai_addr, addr->ai_addrlen)
		    != 0)
		    break;
	    }

	    // If we reached the end of the address list, we've
	    // successfully bound to all appropriate addresses for
	    // this display number, so we can use it.
	    if (addr == NULL)
		return display_num;
	}

	throw std::runtime_error("did not find a free X display");
    }

    void get_random_bytes(unsigned char * buf, int len)
    {
	assert(len > 0);
	auto_fd random_fd(open("/dev/urandom", O_RDONLY));
	if (random_fd.get() == -1 || read(random_fd.get(), buf, len) != len)
	    throw std::runtime_error(std::strerror(errno));
    }

    std::auto_ptr<temp_file> create_temp_auth_file(int display_num)
    {
	std::auto_ptr<temp_file> auth_file(new temp_file("Xvfb-auth-"));

	// An xauth entry consists of the following fields.  All u16 fields
	// are big-endian and unaligned.  Character arrays are not null-
	// terminated.
	// u16     address family (= 256 for local socket)
	// u16     length of address
	// char[]  address (= hostname)
	// u16     length of display number
	// char[]  display number
	// u16     auth type name length
	// char[]  auth type name (= "MIT-MAGIC-COOKIE-1")
	// u16     length of auth data (= 16)
	// char[]  auth data (= random bytes)
	uint16_t family = htons(0x100);
	write(auth_file->get_fd(), &family, sizeof(family));
	utsname my_uname;
	uname(&my_uname);
	uint16_t len = htons(strlen(my_uname.nodename));
	write(auth_file->get_fd(), &len, sizeof(len));
	write(auth_file->get_fd(),
	      my_uname.nodename, strlen(my_uname.nodename));
	char display[15];
	std::sprintf(display, "%d", display_num);
	len = htons(strlen(display));
	write(auth_file->get_fd(), &len, sizeof(len));
	write(auth_file->get_fd(), display, strlen(display));
	static const char auth_type[] = "MIT-MAGIC-COOKIE-1";
	len = htons(sizeof(auth_type) - 1);
	write(auth_file->get_fd(), &len, sizeof(len));
	write(auth_file->get_fd(), auth_type, sizeof(auth_type) - 1);
	unsigned char auth_key[16];
	get_random_bytes(auth_key, sizeof(auth_key));
	len = htons(sizeof(auth_key));
	write(auth_file->get_fd(), &len, sizeof(len));
	write(auth_file->get_fd(), auth_key, sizeof(auth_key));

	return auth_file;
    }

    // Run the X server with the specified auth file, dimensions and
    // assigned display number.
    auto_kill_proc spawn_x_server(int display_num,
				  const std::string & auth_file_name,
				  int width, int height, int depth)
    {
	char display[15];
	std::sprintf(display, ":%d", display_num);
	const char * auth_file_c_str = auth_file_name.c_str();
	std::fflush(NULL);
	auto_kill_proc server_proc(fork());
	if (server_proc.get() == -1)
	    throw std::runtime_error(std::strerror(errno));

	if (server_proc.get() == 0)
	{
	    char dimensions[40];
	    std::sprintf(dimensions, "%dx%dx%d", width, height, depth);
	    execlp("Xvfb",
		   "Xvfb",
		   "-auth", auth_file_c_str,
		   "-nolisten", "tcp",
		   "-screen", "0", dimensions,
		   "-terminate",
		   display,
		   NULL);
	    _exit(128 + errno);
	}

	// Wait for the lock file to appear or the server to exit.  We can't
	// really wait on both of these, so poll at 1-second intervals.
	char lock_file_name[20];
	std::sprintf(lock_file_name, "/tmp/.X%d-lock", display_num);
	for (;;)
	{
	    if (access(lock_file_name, 0) == 0)
		break;
	    if (errno != ENOENT) // huh?
		throw std::runtime_error(std::strerror(errno));
	    if (waitpid(server_proc.get(), NULL, WNOHANG) == server_proc.get())
	    {
		server_proc.release(); // pid is now invalid
		// TODO: Get the exit status and decode it properly.
		throw std::runtime_error("X server failed to create display");
	    }
	    sleep(1);
	}

	return server_proc;
    }
}

x_frame_buffer::x_frame_buffer(int width, int height, int depth)
	: display_num_(select_display_num(tcp4_socket_, tcp6_socket_)),
	  auth_file_(create_temp_auth_file(display_num_)),
	  server_proc_(spawn_x_server(display_num_,
				      get_authority(),
				      width, height, depth))
{}

std::string x_frame_buffer::get_authority() const
{
    return auth_file_->get_name();
}

std::string x_frame_buffer::get_display() const
{
    char display[15];
    std::sprintf(display, ":%d", display_num_);
    return display;
}