TCP connect by using socket return false results

php, sockets, tcp

Solution

The code you link was written a long time ago, when I had a limited understanding of many aspects of non-blocking I/O.

Really this needs an event loop, of which there are many implementations, but for this example I'll use @rdlowrey's Alert library, because it is a minimalist code that should be fairly easy to understand. You can also take a loop at React, which is higher level and provides many more features.

Note that the below example requires PHP 5.4+

<?php

// Array of addresses to test
$addresses = [
    '192.168.5.150',
    '192.168.5.152',
    'google.com',    // Important note: DNS is resolved synchronously here.
    '192.168.5.155', // this can seriously slow down the process as it can block
    '192.168.5.20',  // for a few seconds, async DNS resolution is non-trivial
    '192.168.40.40', // though
];
// The TCP port to test
$port = 80;
// The length of time in seconds to allow host to respond
$timeout = 5;

// This will hold the results
$lookups = [];

// Create a reactor
$reactor = (new \Alert\ReactorFactory)->select();

$count = count($addresses);
$completedCount = 0;

$onComplete = function($address, $result)
                  use(&$lookups, &$completedCount, $count, $reactor) {

    // Cancel the watchers for this address
    $reactor->cancel($lookups[$address]['failWatcher']);
    $reactor->cancel($lookups[$address]['writeWatcher']);
    $reactor->cancel($lookups[$address]['readWatcher']);

    // Store the result
    $lookups[$address] = $result;

    // If there's nothing left to do, stop the reactor
    if (++$completedCount == $count) {
        $reactor->stop();
    }
};

foreach ($addresses as $address) {
    // Normalise the address to lower-case, as it will be used as an array key
    $address = strtolower($address);

    if (!isset($lookups[$address])) {
        // Create a socket to connect asynchronously
        $sockAddr = "tcp://{$address}:{$port}";
        $flags = STREAM_CLIENT_ASYNC_CONNECT;
        $socket = stream_socket_client($sockAddr, $errNo, $errStr, 0, $flags);
        stream_set_blocking($socket, 0);

        // Set up a timeout to watch for failed connections
        $failWatcher = function() use($address, $onComplete, $timeout) {
            echo "{$address} connect failed: Connect timed out\n";
            $onComplete($address, false);
        };
        $failWatcherId = $reactor->once($failWatcher, $timeout);

        // Watch for the stream becoming writable (connection success)
        $writeWatcher = function() use($address, $onComplete) {
            echo "{$address} connected successfully\n";
            $onComplete($address, true);
        };
        $writeWatcherId = $reactor->onWritable($socket, $writeWatcher);

        // Watch for the stream becoming readable (success or explicit fail)
        $readWatcher = function() use($address, $onComplete, $socket) {
            if ('' === $data = fread($socket, 1024)) {
                echo "{$address} connect failed: Server refused connection\n";
                $onComplete($address, false);
            } else if ($data === false) {
                echo "{$address} connect failed: Stream read error\n";
                $onComplete($address, false);
            } else {
                echo "{$address} connected successfully\n";
                $onComplete($address, true);
            }
        };
        $readWatcherId = $reactor->onReadable($socket, $readWatcher);

        // Store the watcher IDs so they can be destroyed later
        $lookups[$address] = [
            'failWatcher'  => $failWatcherId,
            'writeWatcher' => $writeWatcherId,
            'readWatcher'  => $readWatcherId,
        ];
    }
}

// Set everything going
$reactor->run();

// $lookups is now an array of booleans indicating whether the address resulted
// in a successful connection

Problem

Original source

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