The beginnings of a really simple web server written in PHP.

httpd.php

<?php

error_reporting(-1);
set_time_limit(0);

$host = '0.0.0.0';
$port = 12345;
$max_clients = 10;

// Create the socket.
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if (!is_resource($socket)) {
    throw new Exception(socket_last_error());
}

// Bind the socket to the port.
if (!socket_bind($socket, $host, $port) || !socket_listen($socket)) {
    throw new Exception(socket_last_error($socket));
}

echo 'Waiting for connections...',"\n";

$write  = null;
$except = null;
$tv_sec = null;

$new_client = array('socket' => null, 'address' => null, 'input' => '');
$client = array_fill(0, $max_clients, $new_client);

while (true) {
    $read = array($socket);
    for ($i = 0; $i < $max_clients; ++$i) {
        if ($client[$i]['socket'] !== null) {
            $read[] = $client[$i]['socket'];
        }
    }

    if (socket_select($read, $write, $except, $tv_sec) === 0) {
        continue;
    }

    if (in_array($socket, $read)) {
        for ($i = 0; $i < $max_clients; ++$i) {
            if ($client[$i]['socket'] === null) {
                $client[$i]['socket'] = socket_accept($socket);
                if (socket_getpeername($client[$i]['socket'], $address)) {
                    $client[$i]['address'] = $address;
                }

                echo 'New client connected ',$i,"\n";
                break;
            } else if ($i == $max_clients - 1) {
                echo 'Too many clients...',"\n";
            }
        }
    }

    for ($i = 0; $i < $max_clients; ++$i) {
        if ($client[$i]['socket'] === null || !in_array($client[$i]['socket'], $read)) {
            continue;
        }

        $input = socket_read($client[$i]['socket'], 1024, PHP_BINARY_READ);
        $client[$i]['input'] .= $input;

        if (substr($client[$i]['input'], -4) === "\r\n\r\n") {
            $response = 'HTTP/1.1 200 OK'."\r\n".
                'Date: '.date('r')."\r\n".
                'Content-Type: text/html; charset=UTF-8'."\r\n\r\n".
                '<h1>Hello, World!</h1>'."\r\n";
            socket_write($client[$i]['socket'], $response, strlen($response));
            socket_close($client[$i]['socket']);
            echo '>>> ',$client[$i]['address'],"\n",rtrim($client[$i]['input'], "\r\n"),"\n\n";
            $client[$i] = $new_client;
        }
    }
}

// Close primary socket.
socket_close($socket);

echo 'Socket terminated',"\n";