URL-rewriting PHP proxy, works with Apache's userdir module

proxy.php

<?php

function debug_exit($msg) {
  echo ">{$msg}<";
  exit(200);
}

function readFtpLine($line, $s) {
  if ("\r" == substr($line, -1)) {
    socket_read($s, strlen("\n"), PHP_NORMAL_READ);
  }
  return SENTINEL;
}

function startFtpTransfer($s, $host, $resource) {
  forEachBlockRead($s, 1024, PHP_NORMAL_READ, 'readFtpLine');
  # read: 220 welcome message
  # login: USER anonymous
  # read: 331 pwd required
  # pwd: PASS [email protected]
  # read: 230 logged in
  # passive: PASV
  # read: 227 complied
  # get/post file: 
  return FALSE;
}

function writeReconstructedRequest($s, $protocol, $host, $resource) {
  if ("ftp://" === substr($protocol, 0, strlen("ftp://"))) {
    return startFtpTransfer($s, $host, $resource);
  }
  $verb = $_SERVER['REQUEST_METHOD'];
  $line = "{$verb} {$resource} {$_SERVER['SERVER_PROTOCOL']}\r\n";
  if (FALSE === socket_write($s, $line, strlen($line))) {
    return FALSE;
  }
  $heads = " PHP_AUTH_USER PHP_AUTH_PW CONTENT_TYPE CONTENT_LENGTH";
  foreach ($_SERVER as $key=>$value) {
    if ("HTTP_" === substr($key, 0, strlen("HTTP_")) && "HTTP_HOST" !== $key) {
      $header = substr($key, strlen("HTTP_"));
      if ("CONNECTION" === $header) {
        $value = "close";	// since we'll close socket anyway + don't have to keep track of read amount
      } else if ("REFERER" === $header) {
        $pattern = preg_quote("{$_SERVER['HTTP_HOST']}{$_SERVER['SCRIPT_NAME']}/", "/");
        $value = preg_replace("/{$pattern}/", "", $value);
//      } else if ("USER_AGENT" === $header) {
//        continue;
      }
    } elseif (FALSE === strpos($heads, $key)) {
      continue;
    } elseif ("PHP_AUTH_" === substr($key, 0, strlen("PHP_AUTH_"))) {
      $authorization = "Basic ".base64_encode("{$_SERVER['PHP_AUTH_USER']}:{$_SERVER['PHP_AUTH_PW']}");
      continue;
    }
    $header = str_replace("_", "-", $header);
    $line = "{$header}: {$value}\r\n";
    if (FALSE === socket_write($s, $line, strlen($line))) {
      return FALSE;
    }
  }
  $lines = array("Host: {$host}\r\n", "\r\n");
  if (strlen($authorization) > 0) {
    array_unshift($lines, "Authorization: {$authorization}\r\n");
  }
  foreach ($lines as $line) {
    if (FALSE === socket_write($s, $line, strlen($line))) {
      return FALSE;
    }
  }   // FIXME: no php://input when enctype="multipart/form-data"
  $body = fopen("php://input", "r");
  if (FALSE !== $body) {
    for ($bytes = fread($body, 8192); strlen($bytes) > 0; $bytes = fread($body, 8192)) {
      if (FALSE === socket_write($s, $bytes, strlen($bytes))) {
        return FALSE;
      }
    }
    fclose($body);
  }
  fflush($s);
  return TRUE;
}

define(SENTINEL, "aborts forEachBlockRead loop");

function forEachBlockRead($s, $blockSize, $readKind, $functionPointer) {
  $block = socket_read($s, $blockSize, $readKind);
  for (; strlen($block) > 0; $block = socket_read($s, $blockSize, $readKind)) {
    if (SENTINEL === $functionPointer($block, $s)) {
      break;
    }
  }
}

$postponedContent = "";
$printContent = 'printBlock';

function printHeader($line, $s) {
  if ("\r" == substr($line, -1)) {
    socket_read($s, strlen("\n"), PHP_NORMAL_READ);
    if (strlen($line) == 1) {
      return SENTINEL;	// signal last header
    }
  }
  if ("Connection: " === substr($line, 0, strlen("Connection: ")) || "Upgrade: " === substr($line, 0, strlen("Upgrade: "))) {
    return;	// will be provided by out server
  } 
  $line = substr($line, 0, strlen($line) - 1);
  if ("Content-Length: " === substr($line, 0, strlen("Content-Length: "))) {
    global $postponedContent;
    $postponedContent = $line;
    return;
  } elseif ("Location: " === substr($line, 0, strlen("Location: "))) {
    $doubleSlashPos = strpos($line, "://");
    if (FALSE === $doubleSlashPos) {
      $doubleSlashPos = -strlen("://");
    }
    $protocol = substr($line, 0, strlen("://") + $doubleSlashPos);
    $line = "{$protocol}{$_SERVER['HTTP_HOST']}{$_SERVER['SCRIPT_NAME']}/".substr($line, strlen($protocol));
  }
  header($line);
  global $printContent;
  if ("Content-Type: text/html" === substr($line, 0, strlen("Content-Type: text/html"))) {
    $printContent = 'bufferBlock';
  } else if ("Content-Type: application/javascript" === substr($line, 0, strlen("Content-Type: application/javascript"))) {
    $printContent = 'bufferBlock';
  }
}

function printBlock($bytes, $s) {
  global $postponedContent;
  if (isset($postponedContent)) {
    header($postponedContent);
    $postponedContent = NULL;
  }
  echo $bytes;
}

function bufferBlock($lines, $s) {
  global $postponedContent;
  if ("Content-Length: " === substr($postponedContent, 0, strlen("Content-Length: "))) {
    $postponedContent = "";
  }
  $postponedContent .= $lines;
}

function close_status($s, $status, $msg, $nextHeader = NULL) {
  header("{$_SERVER['SERVER_PROTOCOL']} {$status} {$msg}");
  if (isset($nextHeader)) {
    header($nextHeader);
  }
  header("Content-Type: text/plain");
  echo $msg;
  socket_close($s);
  echo "\n<pre>".print_r($_SERVER, TRUE)."</pre>";
}

function connectAndRelayRequest($s, $address, $protocol, $host, $port, $url) {
  if (FALSE === socket_connect($s, $address, $port)) {
    return close_status($s, 503, "{$host}:{$port} is down");
  } elseif (!writeReconstructedRequest($s, $protocol, $host, $url)) {
    return close_status($s, 502, "{$host}:{$port} rejected request");
  }
  header_remove();
  forEachBlockRead($s, 1024, PHP_NORMAL_READ, 'printHeader');
  global $printContent;
  forEachBlockRead($s, 1280, PHP_BINARY_READ, $printContent);
  global $postponedContent;
  if (isset($postponedContent)) {
    $pattern = preg_quote($host);
    header("X-Original-Content-Length: ".strlen($postponedContent));
    $postponedContent = preg_replace("/{$pattern}/", "{$_SERVER['HTTP_HOST']}{$_SERVER['SCRIPT_NAME']}/\\0", $postponedContent);
    header("Content-Length: ".strlen($postponedContent));
    echo $postponedContent;
  }
  socket_close($s);
}

for ($s = socket_create(AF_INET, SOCK_STREAM, SOL_TCP); FALSE !== $s; ) {
  $protocol = preg_replace(".+", "s", $_SERVER['HTTPS']);
  $protocol = "http{$protocol}://";
  $queryPos = strpos($_SERVER['REQUEST_URI'], '?');
  if (FALSE !== $queryPos) {
    $query = substr($_SERVER['REQUEST_URI'], $queryPos);
  }
  $script = $_SERVER['SCRIPT_NAME'];
  for ($url = substr($_SERVER['PHP_SELF'], strlen($script)); "" === $url || substr($url, 0, 1) === "?"; ) {
    return close_status($s, 200, "Usage: {$protocol}{$_SERVER['HTTP_HOST']}{$script}/[{$protocol}]host[:port][/uri][?query]");
  }     // else starts with /
  $url = substr($url, 1);
  if ("ftp://" === substr($url, 0, strlen("ftp://"))) {
    $protocol = "ftp://";
  }
  $protLen = strlen($protocol);
  if (substr($url, 0, $protLen) === $protocol) {
    $url = substr($url, $protLen);
  }
  if (1 != sscanf($url, "%[^:/?]", $host)) {
    return close_status($s, 400, "{$script}/[{$protocol}]host[:port][/uri][?query] expected instead of {$_SERVER['REQUEST_URI']}");
  }
  $url = substr($url, strlen($host));
  $port = $_SERVER['SERVER_PORT'];
  if (1 == sscanf($url, ":%[0-9]", $port)) {
    $portStr = ":{$port}";
    $url = substr($url, strlen($port) + 1);
  }
  if ("" === $url) {
    return close_status($s, 308, "Trailing / required for relative URLs to work", "Location: {$script}/{$host}{$portStr}/");
  }	// else already starts with /
  $address = $host;
  if (!filter_var($address, FILTER_VALIDATE_IP)) {
    $address = "127.0.0.1";
    if ("localhost" !== $host) {
      // TODO: timeouts via http://pear.php.net/package/Net_DNS
      $address = gethostbyname($host);
    }
  }
//  debug_exit("protocol: {$protocol}, address: {$address}, host: {$host}, port: {$port}, url: {$url}, query: {$query}");
  return connectAndRelayRequest($s, $address, $protocol, $host, $port, $url.$query);
}
header("{$_SERVER['SERVER_PROTOCOL']} 500 Failed to create socket");
?>