<?php
namespace React\Dns\Query;
use React\Dns\Model\Message;
use React\Dns\Protocol\BinaryDumper;
use React\Dns\Protocol\Parser;
use React\EventLoop\LoopInterface;
use React\Promise\Deferred;
/**
* Send DNS queries over a TCP/IP stream transport.
*
* This is one of the main classes that send a DNS query to your DNS server.
*
* For more advanced usages one can utilize this class directly.
* The following example looks up the `IPv6` address for `reactphp.org`.
*
* ```php
* $loop = Factory::create();
* $executor = new TcpTransportExecutor('8.8.8.8:53', $loop);
*
* $executor->query(
* new Query($name, Message::TYPE_AAAA, Message::CLASS_IN)
* )->then(function (Message $message) {
* foreach ($message->answers as $answer) {
* echo 'IPv6: ' . $answer->data . PHP_EOL;
* }
* }, 'printf');
*
* $loop->run();
* ```
*
* See also [example #92](examples).
*
* Note that this executor does not implement a timeout, so you will very likely
* want to use this in combination with a `TimeoutExecutor` like this:
*
* ```php
* $executor = new TimeoutExecutor(
* new TcpTransportExecutor($nameserver, $loop),
* 3.0,
* $loop
* );
* ```
*
* Unlike the `UdpTransportExecutor`, this class uses a reliable TCP/IP
* transport, so you do not necessarily have to implement any retry logic.
*
* Note that this executor is entirely async and as such allows you to execute
* queries concurrently. The first query will establish a TCP/IP socket
* connection to the DNS server which will be kept open for a short period.
* Additional queries will automatically reuse this existing socket connection
* to the DNS server, will pipeline multiple requests over this single
* connection and will keep an idle connection open for a short period. The
* initial TCP/IP connection overhead may incur a slight delay if you only send
* occasional queries – when sending a larger number of concurrent queries over
* an existing connection, it becomes increasingly more efficient and avoids
* creating many concurrent sockets like the UDP-based executor. You may still
* want to limit the number of (concurrent) queries in your application or you
* may be facing rate limitations and bans on the resolver end. For many common
* applications, you may want to avoid sending the same query multiple times
* when the first one is still pending, so you will likely want to use this in
* combination with a `CoopExecutor` like this:
*
* ```php
* $executor = new CoopExecutor(
* new TimeoutExecutor(
* new TcpTransportExecutor($nameserver, $loop),
* 3.0,
* $loop
* )
* );
* ```
*
* > Internally, this class uses PHP's TCP/IP sockets and does not take advantage
* of [react/socket](https://github.com/reactphp/socket) purely for
* organizational reasons to avoid a cyclic dependency between the two
* packages. Higher-level components should take advantage of the Socket
* component instead of reimplementing this socket logic from scratch.
*/
class TcpTransportExecutor implements ExecutorInterface
{
private $nameserver;
private $loop;
private $parser;
private $dumper;
/**
* @var ?resource
*/
private $socket;
/**
* @var Deferred[]
*/
private $pending = array();
/**
* @var string[]
*/
private $names = array();
/**
* Maximum idle time when socket is current unused (i.e. no pending queries outstanding)
*
* If a new query is to be sent during the idle period, we can reuse the
* existing socket without having to wait for a new socket connection.
* This uses a rather small, hard-coded value to not keep any unneeded
* sockets open and to not keep the loop busy longer than needed.
*
* A future implementation may take advantage of `edns-tcp-keepalive` to keep
* the socket open for longer periods. This will likely require explicit
* configuration because this may consume additional resources and also keep
* the loop busy for longer than expected in some applications.
*
* @var float
* @link https://tools.ietf.org/html/rfc7766#section-6.2.1
* @link https://tools.ietf.org/html/rfc7828
*/
private $idlePeriod = 0.001;
/**
* @var ?\React\EventLoop\TimerInterface
*/
private $idleTimer;
private $writeBuffer = '';
private $writePending = false;
private $readBuffer = '';
private $readPending = false;
/**
* @param string $nameserver
* @param LoopInterface $loop
*/
public function __construct($nameserver, LoopInterface $loop)
{
if (\strpos($nameserver, '[') === false && \substr_count($nameserver, ':') >= 2 && \strpos($nameserver, '://') === false) {
// several colons, but not enclosed in square brackets => enclose IPv6 address in square brackets
$nameserver = '[' . $nameserver . ']';
}
$parts = \parse_url((\strpos($nameserver, '://') === false ? 'tcp://' : '') . $nameserver);
if (!isset($parts['scheme'], $parts['host']) || $parts['scheme'] !== 'tcp' || !\filter_var(\trim($parts['host'], '[]'), \FILTER_VALIDATE_IP)) {
throw new \InvalidArgumentException('Invalid nameserver address given');
}
$this->nameserver = $parts['host'] . ':' . (isset($parts['port']) ? $parts['port'] : 53);
$this->loop = $loop;
$this->parser = new Parser();
$this->dumper = new BinaryDumper();
}
public function query(Query $query)
{
$request = Message::createRequestForQuery($query);
// keep shuffing message ID to avoid using the same message ID for two pending queries at the same time
while (isset($this->pending[$request->id])) {
$request->id = \mt_rand(0, 0xffff); // @codeCoverageIgnore
}
$queryData = $this->dumper->toBinary($request);
$length = \strlen($queryData);
if ($length > 0xffff) {
return \React\Promise\reject(new \RuntimeException(
'DNS query for ' . $query->name . ' failed: Query too large for TCP transport'
));
}
$queryData = \pack('n', $length) . $queryData;
if ($this->socket === null) {
// create async TCP/IP connection (may take a while)
$socket = @\stream_socket_client($this->nameserver, $errno, $errstr, 0, \STREAM_CLIENT_CONNECT | \STREAM_CLIENT_ASYNC_CONNECT);
if ($socket === false) {
return \React\Promise\reject(new \RuntimeException(
'DNS query for ' . $query->name . ' failed: Unable to connect to DNS server (' . $errstr . ')',
$errno
));
}
// set socket to non-blocking and wait for it to become writable (connection success/rejected)
\stream_set_blocking($socket, false);
$this->socket = $socket;
}
if ($this->idleTimer !== null) {
$this->loop->cancelTimer($this->idleTimer);
$this->idleTimer = null;
}
// wait for socket to become writable to actually write out data
$this->writeBuffer .= $queryData;
if (!$this->writePending) {
$this->writePending = true;
$this->loop->addWriteStream($this->socket, array($this, 'handleWritable'));
}
$names =& $this->names;
$that = $this;
$deferred = new Deferred(function () use ($that, &$names, $request) {
// remove from list of pending names, but remember pending query
$name = $names[$request->id];
unset($names[$request->id]);
$that->checkIdle();
throw new CancellationException('DNS query for ' . $name . ' has been cancelled');
});
$this->pending[$request->id] = $deferred;
$this->names[$request->id] = $query->name;
return $deferred->promise();
}
/**
* @internal
*/
public function handleWritable()
{
if ($this->readPending === false) {
$name = @\stream_socket_get_name($this->socket, true);
if ($name === false) {
$this->closeError('Connection to DNS server rejected');
return;
}
$this->readPending = true;
$this->loop->addReadStream($this->socket, array($this, 'handleRead'));
}
$written = @\fwrite($this->socket, $this->writeBuffer);
if ($written === false || $written === 0) {
$this->closeError('Unable to write to closed socket');
return;
}
if (isset($this->writeBuffer[$written])) {
$this->writeBuffer = \substr($this->writeBuffer, $written);
} else {
$this->loop->removeWriteStream($this->socket);
$this->writePending = false;
$this->writeBuffer = '';
}
}
/**
* @internal
*/
public function handleRead()
{
// read one chunk of data from the DNS server
// any error is fatal, this is a stream of TCP/IP data
$chunk = @\fread($this->socket, 65536);
if ($chunk === false || $chunk === '') {
$this->closeError('Connection to DNS server lost');
return;
}
// reassemble complete message by concatenating all chunks.
$this->readBuffer .= $chunk;
// response message header contains at least 12 bytes
while (isset($this->readBuffer[11])) {
// read response message length from first 2 bytes and ensure we have length + data in buffer
list(, $length) = \unpack('n', $this->readBuffer);
if (!isset($this->readBuffer[$length + 1])) {
return;
}
$data = \substr($this->readBuffer, 2, $length);
$this->readBuffer = (string)substr($this->readBuffer, $length + 2);
try {
$response = $this->parser->parseMessage($data);
} catch (\Exception $e) {
// reject all pending queries if we received an invalid message from remote server
$this->closeError('Invalid message received from DNS server');
return;
}
// reject all pending queries if we received an unexpected response ID or truncated response
if (!isset($this->pending[$response->id]) || $response->tc) {
$this->closeError('Invalid response message received from DNS server');
return;
}
$deferred = $this->pending[$response->id];
unset($this->pending[$response->id], $this->names[$response->id]);
$deferred->resolve($response);
$this->checkIdle();
}
}
/**
* @internal
* @param string $reason
*/
public function closeError($reason)
{
$this->readBuffer = '';
if ($this->readPending) {
$this->loop->removeReadStream($this->socket);
$this->readPending = false;
}
$this->writeBuffer = '';
if ($this->writePending) {
$this->loop->removeWriteStream($this->socket);
$this->writePending = false;
}
if ($this->idleTimer !== null) {
$this->loop->cancelTimer($this->idleTimer);
$this->idleTimer = null;
}
@\fclose($this->socket);
$this->socket = null;
foreach ($this->names as $id => $name) {
$this->pending[$id]->reject(new \RuntimeException(
'DNS query for ' . $name . ' failed: ' . $reason
));
}
$this->pending = $this->names = array();
}
/**
* @internal
*/
public function checkIdle()
{
if ($this->idleTimer === null && !$this->names) {
$that = $this;
$this->idleTimer = $this->loop->addTimer($this->idlePeriod, function () use ($that) {
$that->closeError('Idle timeout');
});
}
}
}