Privacy Image Cache

diff --git a/privacy_image_cache/README.md b/privacy_image_cache/README.md
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+Once activated, this addon acs as a proxy between the user and external image resources.
+If external images are to be shown, like avatars or embedded images, the server retrieves the image and the local link is sent to the user.
+By using this proxy, the server hosting the original image cannot retrieve personal information of the user like the IP address, User Agent or Cookies.
+However, the remote server will be able to track the IP address of the server hosting the friendica installation.
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diff --git a/privacy_image_cache/privacy_image_cache.php b/privacy_image_cache/privacy_image_cache.php
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+<?php
+
+/**
+ * Name: Privacy Image Cache
+ * Version: 0.1
+ * Author: Tobias Hößl <https://github.com/CatoTH/>
+ */
+
+define("PRIVACY_IMAGE_CACHE_DEFAULT_TIME", 86400); // 1 Day
+
+require_once('include/security.php');
+
+function privacy_image_cache_install() {
+    register_hook('bbcode',       'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_bbcode_hook');
+    register_hook('display_item', 'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_display_item_hook');
+    register_hook('ping_xmlize',  'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_ping_xmlize_hook');
+    register_hook('cron',         'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_cron');
+}
+
+
+function privacy_image_cache_uninstall() {
+    unregister_hook('bbcode',       'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_bbcode_hook');
+    unregister_hook('display_item', 'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_display_item_hook');
+    unregister_hook('ping_xmlize',  'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_ping_xmlize_hook');
+    unregister_hook('cron',         'addon/privacy_image_cache/privacy_image_cache.php', 'privacy_image_cache_cron');
+}
+
+
+function privacy_image_cache_module() {}
+
+
+function privacy_image_cache_init() {
+    $urlhash = 'pic:' . sha1($_REQUEST['url']);
+    $r = q("SELECT * FROM `photo` WHERE `resource-id` = '%s' LIMIT 1", $urlhash );
+    if (count($r)) {
+        $img_str = $r[0]['data'];
+    }
+    else {
+        require_once("Photo.php");
+
+        $img_str = fetch_url($_REQUEST['url'],true);
+        $img = new Photo($img_str);
+        if($img->is_valid()) {
+            $img->store(0, 0, $urlhash, $_REQUEST['url'], '', 100);
+            $img_str = $img->imageString();
+        }
+    }
+
+
+    header("Content-type: image/jpeg");
+    header("Expires: " . gmdate("D, d M Y H:i:s", time() + (3600*24)) . " GMT");
+    header("Cache-Control: max-age=" . (3600*24));
+
+    echo $img_str;
+
+    killme();
+}
+
+/**
+ * @param $url string
+ * @return boolean
+ */
+function privacy_image_cache_is_local_image($url) {
+    if ($url[0] == '/') return true;
+    $baseurl = get_app()->get_baseurl();
+    return (substr($url, 0, strlen($baseurl)) == $baseurl);
+}
+
+/**
+ * @param array $matches
+ * @return string
+ */
+function privacy_image_cache_img_cb($matches) {
+    if (privacy_image_cache_is_local_image($matches[2])) return $matches[2];
+    return $matches[1] . "/privacy_image_cache/?url=" . escape_tags(addslashes($matches[2])) . $matches[3];
+}
+
+/**
+ * @param App $a
+ * @param string $o
+ */
+function privacy_image_cache_bbcode_hook(&$a, &$o) {
+    $o = preg_replace_callback("/(<img [^>]*src *= *[\"'])([^\"']+)([\"'][^>]*>)/siU", "privacy_image_cache_img_cb", $o);
+}
+
+
+/**
+ * @param App $a
+ * @param string $o
+ */
+function privacy_image_cache_display_item_hook(&$a, &$o) {
+    if (isset($o["output"])) {
+        if (isset($o["output"]["thumb"]) && !privacy_image_cache_is_local_image($o["output"]["thumb"]))
+            $o["output"]["thumb"] = "/privacy_image_cache/?url=" . escape_tags(addslashes($o["output"]["thumb"]));
+        if (isset($o["output"]["author-avatar"]) && !privacy_image_cache_is_local_image($o["output"]["author-avatar"]))
+            $o["output"]["author-avatar"] = "/privacy_image_cache/?url=" . escape_tags(addslashes($o["output"]["author-avatar"]));
+    }
+}
+
+
+/**
+ * @param App $a
+ * @param string $o
+ */
+function privacy_image_cache_ping_xmlize_hook(&$a, &$o) {
+    if ($o["photo"] != "" && !privacy_image_cache_is_local_image($o["photo"]))
+        $o["photo"] = "/privacy_image_cache/?url=" . escape_tags(addslashes($o["photo"]));
+}
+
+
+/**
+ * @param App $a
+ * @param null|object $b
+ */
+function privacy_image_cache_cron(&$a, &$b) {
+    $cachetime = get_config('privacy_image_cache','cache_time');
+    if (!$cachetime) $cachetime = PRIVACY_IMAGE_CACHE_DEFAULT_TIME;
+
+    $last = get_config('pi_cache','last_delete');
+    $time = time();
+    if ($time < ($last + 3600)) return;
+
+    logger("Purging old Cache of the Privacy Image Cache", LOGGER_DEBUG);
+    q('DELETE FROM `photo` WHERE `uid` = 0 AND `resource-id` LIKE "pic:%%" AND `created` < NOW() - INTERVAL %d SECOND', $cachetime);
+    set_config('pi_cache', 'last_delete', $time);
+}
+
+
+
+
+/**
+ * @param App $a
+ * @param null|object $o
+ */
+function privacy_image_cache_plugin_admin(&$a, &$o){
+
+
+    $o = '<input type="hidden" name="form_security_token" value="' . get_form_security_token("picsave") . '">';
+
+    $cachetime = get_config('privacy_image_cache','cache_time');
+    if (!$cachetime) $cachetime = PRIVACY_IMAGE_CACHE_DEFAULT_TIME;
+    $cachetime_h = Ceil($cachetime / 3600);
+
+    $o .= '<label for="pic_cachetime">' . t('Lifetime of the cache (in hours)') . '</label>
+        <input id="pic_cachetime" name="cachetime" type="text" value="' . escape_tags($cachetime_h) . '"><br style="clear: both;">';
+
+    $o .= '<input type="submit" name="save" value="' . t('Save') . '">';
+
+    $o .= '<h4>' . t('Cache Statistics') . '</h4>';
+
+    $num = q('SELECT COUNT(*) num, SUM(LENGTH(data)) size FROM `photo` WHERE `uid`=0 AND `contact-id`=0 AND `resource-id` LIKE "pic:%%"');
+    $o .= '<label for="statictics_num">' . t('Number of items') . '</label><input style="color: gray;" id="statistics_num" disabled value="' . escape_tags($num[0]['num']) . '"><br style="clear: both;">';
+    $size = Ceil($num[0]['size'] / (1024 * 1024));
+    $o .= '<label for="statictics_size">' . t('Size of the cache') . '</label><input style="color: gray;" id="statistics_size" disabled value="' . $size . ' MB"><br style="clear: both;">';
+
+    $o .= '<input type="submit" name="delete_all" value="' . t('Delete the whole cache') . '">';
+}
+
+
+/**
+ * @param App $a
+ * @param null|object $o
+ */
+function privacy_image_cache_plugin_admin_post(&$a, &$o){
+    check_form_security_token_redirectOnErr('/admin/plugins/privacy_image_cache', 'picsave');
+
+    if (isset($_REQUEST['save'])) {
+        $cachetime_h = IntVal($_REQUEST['cachetime']);
+        if ($cachetime_h < 1) $cachetime_h = 1;
+        set_config('privacy_image_cache','cache_time', $cachetime_h * 3600);
+    }
+    if (isset($_REQUEST['delete_all'])) {
+        q('DELETE FROM `photo` WHERE `uid` = 0 AND `resource-id` LIKE "pic:%%"');
+    }
+}
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