<?php

/**
 * I was having trouble with socket connections timing out reliably. Sometimes,
 * my timeout would be reached. Other times, the connect would fail after three
 * to six seconds. I finally figured out it had to do with trying to connect to
 * a routable, non-localhost address. It seems the socket_connect call would
 * not fail immediately for those connections. This function is what I finally
 * ended up with that reliably connects to a working server, fails quickly for
 * a server that has an address/port that is not reachable and will reach the
 * timeout for routable addresses that are not up.
 *
 * Copyright (c) 2015, Brian Moon of DealNews.com, Inc. 
 * All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met: 
 * 
 *  * Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 *  * Redistributions in binary form must reproduce the above 
 *    copyright notice, this list of conditions and the following 
 *    disclaimer in the documentation and/or other materials provided 
 *    with the distribution. 
 *  * Neither the name of DealNews.com Inc. nor the names of its 
 *    contributors may be used to endorse or promote products derived 
 *    from this software without specific prior written permission. 
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 
 * OF THE POSSIBILITY OF SUCH DAMAGE. 
 *  
 */

/**
 * Example:
 *
 * Assuming these hosts are valid for your setup, this example would produce
 * something like this:
 *
 * Trying: Good host...
 * resource(10) of type (Socket)
 * 
 * Trying: Routable, but not up...
 * Failed to connect to 10.1.2.30:4730. (timed out after 102.1051ms)
 * NULL
 * 
 * Trying: Up but not listening...
 * Failed to connect to 127.0.0.1:7676. (111: Connection refused; after 0.051ms)
 * NULL
 *
 * =====
 * 
 * $timeout = 100;
 * 
 * $hosts = array(
 *     array(
 *         "desc" => "Good host",
 *         "host" => "127.0.0.1",
 *         "port" => "4730"
 *     ),
 *     array(
 *         "desc" => "Routable, but not up",
 *         "host" => "10.1.2.30",
 *         "port" => "4730"
 *     ),
 *     array(
 *         "desc" => "Up but not listening",
 *         "host" => "127.0.0.1",
 *         "port" => "7676"
 *     ),
 * );
 * 
 * foreach($hosts as $host){
 * 
 *     echo "Trying: $host[desc]...\n";
 * 
 *     try{
 *         $socket = socket_connect_timeout($host["host"], $host["port"], $timeout);
 *     } catch(Exception $e){
 *         echo $e->getMessage()."\n";
 *         $socket = null;
 *     }
 * 
 *     var_dump($socket);
 * 
 *     echo "\n";
 * 
 * }
 *
 */

 function socket_connect_timeout($host, $port, $timeout=100){

    $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);

    /**
     * Set the send and receive timeouts super low so that socket_connect
     * will return to us quickly. We then loop and check the real timeout
     * and check the socket error to decide if its conected yet or not.
     */
    $connect_timeval = array(
        "sec"=>0,
        "usec" => 100
    );
    socket_set_option(
        $socket,
        SOL_SOCKET,
        SO_SNDTIMEO,
        $connect_timeval
    );
    socket_set_option(
        $socket,
        SOL_SOCKET,
        SO_RCVTIMEO,
        $connect_timeval
    );

    $now = microtime(true);

    /**
     * Loop calling socket_connect. As long as the error is 115 (in progress)
     * or 114 (already called) and our timeout has not been reached, keep
     * trying.
     */
    $err = null;
    $socket_connected = false;
    do{
        socket_clear_error($socket);
        $socket_connected = @socket_connect($socket, $host, $port);
        $err = socket_last_error($socket);
        $elapsed = (microtime(true) - $now) * 1000;
    }
    while (($err === 115 || $err === 114) && $elapsed < $timeout);

    /**
     * For some reason, socket_connect can return true even when it is
     * not connected. Make sure it returned true the last error is zero
     */
    $socket_connected = $socket_connected && $err === 0;

    if($socket_connected){

        /**
         * Set keep alive on so the other side does not drop us
         */
        socket_set_option($socket, SOL_SOCKET, SO_KEEPALIVE, 1);

        /**
         * set the real send/receive timeouts here now that we are connected
         */
        $timeval = array(
            "sec" => 0,
            "usec" => 0
        );
        if($timeout >= 1000){
            $ts_seconds = $timeout / 1000;
            $timval["sec"] = floor($ts_seconds);
            $timval["usec"] = ($ts_seconds - $tv_sec) * 1000000;
        } else {
            $timval["usec"] = $timeout * 1000;
        }
        socket_set_option(
            $socket,
            SOL_SOCKET,
            SO_SNDTIMEO,
            $timeval
        );
        socket_set_option(
            $socket,
            SOL_SOCKET,
            SO_RCVTIMEO,
            $timeval
        );

    } else {

        $elapsed = round($elapsed, 4);

        if(!is_null($err) && $err !== 0 && $err !== 114 && $err !== 115){
            $message = "Failed to connect to $host:$port. ($err: ".socket_strerror($err)."; after {$elapsed}ms)";
        } else {
            $message = "Failed to connect to $host:$port. (timed out after {$elapsed}ms)";
        }

        throw new Exception($message);

    }

    return $socket;

}