proxy.php

<?php

/**
 *
 * PHP PROXY
 *
 * ------------------------------------------------------------------------
 *
 * Copyright (c) 2014 Dan Cotora
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>
 *
 * ------------------------------------------------------------------------
 *
 * The proxy endpoint URL should be specified in the GET or POST parameters as endpoint=http://...
 *
 * The proxy forwards the original request to the endpoint URL
 * and returns the response back to the original caller
 *
 * Currently only GET and POST requests are supported. On HEAD, PUT, or DELETE requests,
 * the proxy will return a "400 Bad Request" response
 *
 * If a request fails because of a CURL error (endpoint unavailable, network is down, etc.)
 * the proxy responds with a 502 Bad Gateway status
 *
 */

// Set error reporting level
error_reporting(E_ALL ^ E_NOTICE);

set_time_limit(0);

// ================================
// ===== FUNCTION DEFINITIONS =====
// ================================

/**
 * Get the original request headers
 *
 * Returns an array of headers
 */
function getRequestHeaders()
{
 // Initialize the headers list
 $headers = array();

 // Go trough all the $_SERVER values and extract the request headers
 foreach ($_SERVER as $key => $value) {
 if (substr($key, 0, 5) === "HTTP_") {
 $key = str_replace('_', ' ', substr($key, 5));
 $key = str_replace(' ', '-', ucwords(strtolower($key)));
 $headers[$key] = $value;
 }
 }

 // Return the headers
 return $headers;
}

/**
 * Proxy a request to the specified URL (using CURL)
 *
 * $url - The endpoint URL
 * $method - The HTTP method
 * $headers - An array with the headers that should be sent with the request
 * $data - The GET or POST data that should be included with the request
 *
 * Returns and array with the request & response headers and response body
 *
 * Throws an exception if a CURL error occurs
 */
function sendProxyRequest($url, $method, $headers, $data = array())
{

 // Transform the headers array from the key => value format in the one CURL expects
 $curlHeaders = array();
 foreach ($headers as $key => $value) {
 array_push($curlHeaders, $key . ': ' . $value);
 }

 // Initialize the curl request
 $ch = curl_init();

 // If this is a GET request, append the data to the URL
 if ($method === 'GET') {
 // Add the ? symbol at the end of the URL if the URL doesn't contain any other parameters
 if (strpos($url, '?') === false) {
 $url .= '?';
 } else {
 $url .= '&';
 }

 // Add the get parameters
 foreach($data as $key => $value) {
 $url .= rawurlencode($key) . '=' . rawurlencode($value) . '&';
 }

 // Trim the trailing extra & from the url
 $url = rtrim($url, '&');
 }

	// Set the endpoint URL
 curl_setopt($ch, CURLOPT_URL, $url);

 // Forward the specified headers
 curl_setopt($ch, CURLOPT_HTTPHEADER, $curlHeaders);

 // Configure CURL to return the transfer
 curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

 // Configure CURL to return the response headers
 curl_setopt($ch, CURLOPT_HEADER, 1);

 // Uncomment the following line to always force HTTP 1.0 and prevent chunked transfers
 // Force HTTP 1.0 to prevent chunked transfers
 // curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_0);

 // Configure CURL to return the original request headers so we can log them
 curl_setopt($ch, CURLINFO_HEADER_OUT, 1);

 // Configure the CURL connection timeout to 120 seconds
 curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 120);

 // If this is a POST request, include the post fields with the request
 if ($method === 'POST') {
 curl_setopt($ch, CURLOPT_POST, 1);
 curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
 }

 // Execute the CURL request
 $response = curl_exec($ch);

 // Get the original request headers
 $requestHeders = curl_getinfo($ch, CURLINFO_HEADER_OUT);

 // If an invalid response was received, throw an exception
 if ($response === false) {
 // Get the curl error message and error code
 $message = curl_error($ch);
 $code = curl_errno($ch);

 // Close the curl handle
 curl_close($ch);

 // Throw the exception
 throw new Exception($message, $code);
 }

 // Close the curl handle
 curl_close($ch);

 // If the received response contains 100 Continue, remove it from the response
 if (0 === strpos($response, "HTTP/1.1 100 Continue\r\n\r\n")) {
 $response = substr($response, 25);
 }

 // Get the response headers and body
 list($responseHeaders, $responseBody) = explode("\r\n\r\n", $response, 2);

 // Trim extra new lines from the response headers
 $requestHeders = rtrim($requestHeders);

 // Return the response
 return array(
 'requestHeders' => $requestHeders,
 'responseHeaders' => $responseHeaders,
 'responseBody' => $responseBody
 );
}

// =====================
// ===== MAIN CODE =====
// =====================

// Get the HTTP request method
if (isset($_SERVER['REQUEST_METHOD'])) {
 $requestMethod = strtoupper($_SERVER['REQUEST_METHOD']);
} else {
 echo "Please run this script under a web server" . PHP_EOL;
 exit -1;
}

// Get the original requester's IP address
$senderIP = "Unknown";
if (isset($_SERVER["REMOTE_ADDR"])) {
 $senderIP = $_SERVER["REMOTE_ADDR"];
}

// If this isn't a GET or POST request return the appropriate response
if (!in_array($requestMethod, array('GET', 'POST'))) {
 // Return a 400 Bad Request response and exit
 header('HTTP/1.1 400 Bad Request');
 die();
}

// Get the endpoint URL
$url = $_GET['endpoint'] ? $_GET['endpoint'] : $_POST['endpoint'];

// If the URL is empty or is invalid, return the appropriate response
$isURLEmpty = empty($url);
$isURLValid = filter_var($url, FILTER_VALIDATE_URL) !== false;

if ($isURLEmpty || !$isURLValid) {
 // Return a 400 Bad Request response and exit
 header('HTTP/1.1 400 Bad Request');
 die();
}

// Get the original request headers
$requestHeders = getRequestHeaders();

// Unset the headers that should not be forwarded by the proxy
unset($requestHeders['Host']);
unset($requestHeders['Content-Length']);
unset($requestHeders['Connection']);

// Add the Content-Type header based on the original content type
if (isset($_SERVER['CONTENT_TYPE'])) {
 $requestHeders['Content-Type'] = $_SERVER['CONTENT_TYPE'];
}

// Add the X-Forwarded-For header
$requestHeders['X-Forwarded-For'] = isset($requestHeders['X-Forwarded-For']) ? $senderIP . ',' . $requestHeders['X-Forwarded-For'] : $senderIP;

// Initialize the data that should be forwarded
$data = array();

if ($requestMethod === 'GET') {
 // Get the original parameters sent via GET
 $data = $_GET;

 // Unset the parameters that are used internally by the proxy
 unset($data['endpoint']);

} elseif ($requestMethod === 'POST') {
 // If this is a multipart/form-data request, just use the parsed data
 // (PHP insists to parse this and it doesn't offer access to the raw POST data)
 if (preg_match('/^multipart\/form\-data/', $requestHeders['Content-Type'])) {
 $data = $_POST;

 // Set the correct content type (override the previous one)
 $requestHeders['Content-Type'] = 'multipart/form-data';

 // Unset the parameters that are used internally by the proxy
 unset($data['endpoint']);
 } else {
 // Use the raw POST data and keep the original content type
 $data = file_get_contents('php://input');
 }
}

try {
 // Proxy the request to the specified endpoint
 $result = sendProxyRequest($url, $requestMethod, $requestHeders, $data);

} catch (Exception $ex) {
 // Return a 502 Bad Gateway and exit
 header('HTTP/1.1 502 Bad Gateway');
 die();
}

// Send out the response headers, but skip any "Transfer-Encoding" headers
// Also identify any Content-Type & Content-Encoding headers in the response to determine if the content is binary or not
$responseHeaders = explode("\n", $result['responseHeaders']);
$contentType = null;
$contentEncoding = null;

foreach ($responseHeaders as $header) {
 if (!preg_match('/^Transfer-Encoding/i', $header)) {
 header($header);
 }

 // Extract the Content-Type header's value
 if (preg_match('/^Content-Type:/i', $header)) {
 $contentType = strtolower(trim(substr($header, strpos($header, ':') + 1)));
 if ($pos = strpos($contentType, ';')) $contentType = substr($contentType, 0, $pos);
 }

 // Extract the Content-Encoding header's value
 if (preg_match('/^Content-Encoding:/i', $header)) {
 $contentEncoding = strtolower(trim(substr($header, strpos($header, ':') + 1)));
 }
}

// Send out the response body
echo $result['responseBody'];