<?php
###############################################################################
# Image Proxy - plugin for Gregarius
# Copyright (C) 2006  Dwayne C. Litzenberger <dlitz@dlitz.net>
###############################################################################
# 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, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
###############################################################################

/// Name: Image Proxy
/// Author: Dwayne C. Litzenberger
/// Description: This plugin proxies images that might otherwise be protected by a "referer check".
/// Configuration: __imageproxy_config
/// Version: 0.9
define('IMAGEPROXY_VERSION', '0.9');

define('IMAGEPROXY_CONFIG_HASHKEY', 'imageproxy.hash_key');
define('IMAGEPROXY_HASHKEY_LENGTH', 16);        # 128 bits

function __imageproxy_urlencode_cb($m)
{
    return rawurlencode($m[1]);
}

function __imageproxy_urlencode($s)
{
    // cURL doesn't do _any_ URL encoding, so URLs like
    // "http://example.com/big image.jpg" get sent in the request as
    // "GET /big image.jpg HTTP/1.1", which obviously doesn't work.
    // RFC 2396 section 2.4.3 lists some "Excluded US-ASCII Characters", which
    // we escape here.
    return preg_replace_callback(
        '#([\x00-\x1f\x7f <>"{}|\\^+\[\]`])#s',
        '__imageproxy_urlencode_cb', $s);
}

function __imageproxy_gregarius_version_is_at_least($minver)
{
    $ver = explode('.', _VERSION_);
    $min = explode('.', $minver);
    for ($i = 0; $i < min(count($ver), count($min)); $i++) {
        if ($ver[$i] < $min[$i]) {
            return false;
        }
    }
    return true;
}

function __imageproxy_random($bytes)
{
    # Generate random bits
    _pf("__imageproxy_random");
    if (function_exists("mcrypt_create_iv")) {
        _pf("... using mcrypt_create_iv to generate key");
        $data = mcrypt_create_iv($bytes, MCRYPT_DEV_URANDOM);
        if (!$data) {
            // SECURITY: This is insecure
            _pf("... Warning: generating insecure key using MCRYPT_RAND");
            srand();
            $data = mcrypt_create_iv($bytes, MCRYPT_RAND);
        } else {
            _pf("... key generated using MCRYPT_DEV_URANDOM");
        }
    } else {
        // SECURITY: This is insecure
        _pf("... Warning: generating insecure key using mt_rand");
        mt_srand();
        $data = "";
        for($i = 0; $i < $bytes; $i++) {
            $data .= chr(mt_rand(0, 255));
        }
    }
    if (!isset($data) or !$data or strlen($data) != $bytes) {
        _pf("... error");
        die("Internal error while generating random data");
    }
    return $data;
}

function __imageproxy_make_hash($url, $hash_key=null)
{
    # Hash format:
    #   url = *OCTET
    #   key = 16OCTET           ; the hash key
    #   url-length = 1*DIGIT    ; length of the url
    #   unique = "36:6338dc36-5add-11db-8783-001617467794,"
    #   key-ns = "16:" key ","
    #   url-ns = url-length ":" url ","
    #   hash-data = unique key-ns url-ns
    #   hash = BIN2HEX( SHA1( SHA1( hash-data ) ) )
    # Test vector:
    #   key = "ABCDEFGHIJKLMNOP"  (hex: 4142434445464748494a4b4c4d4e4f50)
    #   url = "about:blank"
    #   hash-data = "36:6338dc36-5add-11db-8783-001617467794,16:ABCDEFGHIJKLMNOP,11:about:blank,"
    #   hash = "1d6f8564bc3555f00ebda1a6b1a349741688d4e6"

    if (!__imageproxy_is_valid_key($hash_key)) {
        $hash_key = __imageproxy_get_key();
    }
    $binary_hash_key = pack('H*', $hash_key);

    $uuid = "6338dc36-5add-11db-8783-001617467794";
    $hash = sha1(sha1(
        strlen($uuid) . ":" . $uuid . "," .
        strlen($binary_hash_key) . ":" . $binary_hash_key . "," .
        strlen($url) . ":" . $url . ",", true));
    return $hash;
}

function __imageproxy_config()
{
    $encoding = (getConfig('rss.output.encoding') ? getConfig('rss.output.encoding') : DEFAULT_OUTPUT_ENCODING);
    $hash_key = __imageproxy_get_key();
    if (rss_plugins_is_submit()) {
        $hash_key = $_REQUEST['hash_key'];
        if (!__imageproxy_is_valid_key($hash_key)) {
            // The specified key is invalid.  Generate a new one.
            $hash_key = __imageproxy_generate_key();
        } else {
            // Normalize the key
            $hash_key = bin2hex(pack('H*', $hash_key));
        }
        // Save the key in the database
        rss_plugins_add_option(IMAGEPROXY_CONFIG_HASHKEY, $hash_key, 'string', 'x');
        return;
    }

    print "<fieldset>\n";
    print "  <legend>" .  rss_htmlspecialchars(__('Security')) . "</legend>\n";
    print "  <p><label for=\"hash_key\">" . rss_htmlspecialchars(__('Hash key (hexadecimal):')) . "</label><br />\n";
    print "  <input id=\"hash_key\" name=\"hash_key\" type=\"text\""
            . " size=\"".intval(IMAGEPROXY_HASHKEY_LENGTH * 2.5)."\""
            . " maxlength=\"".(IMAGEPROXY_HASHKEY_LENGTH * 2)."\""
            . " value=\"" . htmlspecialchars($hash_key, ENT_COMPAT, $encoding) . "\"/></p>";
    print "  <p>" . rss_htmlspecialchars(__('Required length (in hexadecimal digits):')) . " " . (IMAGEPROXY_HASHKEY_LENGTH * 2) . "</p>\n";
    print "  <p>" . rss_htmlspecialchars(__('Entering a blank or invalid key will cause a new key to be generated.')) . "</p>\n";
    print "</fieldset>\n";
}

function __imageproxy_generate_key()
{
    return bin2hex(__imageproxy_random(IMAGEPROXY_HASHKEY_LENGTH));
}

function __imageproxy_get_key()
{
    $hash_key = rss_plugins_get_option(IMAGEPROXY_CONFIG_HASHKEY);
    if (!__imageproxy_is_valid_key($hash_key)) {
        $hash_key = __imageproxy_generate_key();
        rss_plugins_add_option(IMAGEPROXY_CONFIG_HASHKEY, $hash_key, 'string', 'x');
    }
    return $hash_key;
}

function __imageproxy_is_valid_key($hash_key)
{
    if (empty($hash_key)) {
        return false;
    }
    $tmp = @pack('H*', $hash_key);
    if (empty($tmp) or strlen($tmp) != IMAGEPROXY_HASHKEY_LENGTH) {
        return false;
    }
    return true;
}

function __imageproxy_changeSrc__cb($m)
{
    $pre = $m[1];
    $src = $m[2];
    $post = $m[3];
    
    $encoding = (getConfig('rss.output.encoding') ? getConfig('rss.output.encoding') : DEFAULT_OUTPUT_ENCODING);
    
    $q = substr($src, 0, 1);
    $q2 = substr($src, strlen($src)-1, 1);
    if ($q === $q2 and ($q === "'" or $q === '"')) {
        $url = html_entity_decode(substr($src, 1, strlen($src)-2), ENT_QUOTES, $encoding);
    } else {
        $url = html_entity_decode($src, ENT_QUOTES, $encoding);
    }
    
    $hash = __imageproxy_make_hash($url);
    $url = rss_plugins_get_plugins_http_path() . "imageproxy.php?do_proxy=1&hash=".urlencode($hash)."&url=" . urlencode($url);

    return $pre . '"' . htmlspecialchars($url, ENT_COMPAT, $encoding) . '"' . $post;
}


function __imageproxy_filter($item)
{
    if (!array_key_exists('description', $item)) {
        return $item;
    }
    $content = $item->description;
    $content = preg_replace_callback(
        '#(<img\s[^<>]*(?<=\s)src=)("[^<>"]*"|\'[^<>\']*\'|[^<>\s]*)(?=[>\s])([^<>]*>)#is',
        '__imageproxy_changeSrc__cb',
        $content);
    $item->description = $content;
    return $item;
}

function __imageproxy_send_badimage()
{
    $data = base64_decode('R0lGODlhBQAFAIABAP8AAP///ywAAAAABQAFAAACB0RueWHIjwoAOw==');
    header('HTTP/1.0 403 Forbidden');
    header('Content-Type: image/gif');
    header('Content-Length: ' . strlen($data));
    print $data;
    exit;
}

function __imageproxy_do_proxy()
{
    $url = $_REQUEST['url'];
    $hash = $_REQUEST['hash'];
    $referer = @$_SERVER['HTTP_REFERER'];

    // Hash check
    $real_hash = __imageproxy_make_hash($url);
    if ($hash !== $real_hash) {
        header("x-plugin: Invalid hash");
        __imageproxy_send_badimage();
        return;
    }

    // Referer check
    if (!empty($referer)) {
        $u = parse_url($referer);
        if ($u['host'] !== $_SERVER['HTTP_HOST']) {
            header('x-plugin: Illegal referer');
            __imageproxy_send_badimage();
            return;
        }
    }

    // HACK - See the comments on __imageproxy_urlencode above.
    $url = __imageproxy_urlencode($url);

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_HEADER, false);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
    curl_setopt($ch, CURLOPT_MAXREDIRS, 5);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array('X-Forwarded-For: '.$_SERVER['REMOTE_ADDR']));
    curl_setopt($ch, CURLOPT_USERAGENT, "Gregarius-Plugin-ImageProxy/".IMAGEPROXY_VERSION);
    ob_start();
    curl_exec($ch);
    $data = ob_get_clean();
    if (curl_errno($ch) != 0) {
        die("curl fetch failed on url '$url': " . curl_error($ch));
    }
    $content_type = preg_replace('#[\\r\\n]#s', ' ', curl_getinfo($ch, CURLINFO_CONTENT_TYPE));
    curl_close($ch);
    header("Content-Type: " . $content_type);
    header("Content-Length: " . strlen($data));
    print $data;
    exit;
}

if (isset($_REQUEST['do_proxy'])) {
    require_once "../init.php";
    __imageproxy_do_proxy();
}

if (!function_exists("__") and !__imageproxy_gregarius_version_is_at_least("0.5.5")) {
    // Old versions of gregarius don't have localization.  Declare a dummy function.
    function __($s) { return $s; }
}

rss_set_hook('rss.plugins.items.beforerender', '__imageproxy_filter');

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