move blacklist checking into a function

controllers/API.php

@@ -84,6 +84,14 @@ class API {
       ]);
     }
 
+    # Check the blacklist of domains that are known to not accept webmentions
+    if($target && !Telegraph\Webmention::isProbablySupported($target)) {
+      return $this->respond($response, 400, [
+        'error' => 'not_supported',
+        'error_description' => 'The target domain is known to not accept webmentions. If you believe this is in error, please file an issue at https://github.com/aaronpk/Telegraph/issues'
+      ]);
+    }
+
     # Synchronously check the source URL and verify that it actually contains
     # a link to the target. This way we prevent this API from sending known invalid mentions.
     $sourceData = $this->http->get($source);

controllers/Controller.php

@@ -213,16 +213,7 @@ class Controller {
 
     $targetURL = $request->get('target');
 
-    // Reject links that are known to not accept webmentions
-    $host = str_replace('www.','',parse_url($targetURL, PHP_URL_HOST));
-
-    $unsupported = [
-      'twitter.com',
-      'instagram.com',
-      'facebook.com',
-    ];
-
-    if(!$host || in_array($host, $unsupported) || preg_match('/.+\.amazonaws\.com/', $host)) {
+    if(!Telegraph\Webmention::isProbablySupported($targetURL)) {
       $status = 'none';
       $cached = -1;
     } else {

lib/Telegraph/Webmention.php

@@ -7,6 +7,28 @@ class Webmention {
 
   private static $http = false;
 
+  // Returns false if the target URL is known to not accept webmentions
+  public static function isProbablySupported($targetURL) {
+    // Reject links that are known to not accept webmentions
+    $host = str_replace('www.','',parse_url($targetURL, PHP_URL_HOST));
+
+    if(!$host) return false;
+
+    $unsupported = [
+      'twitter.com',
+      'instagram.com',
+      'facebook.com',
+    ];
+
+    if(in_array($host, $unsupported))
+      return false;
+
+    if(preg_match('/.+\.amazonaws\.com/', $host))
+      return false;
+
+    return true;
+  }
+
   private static function updateStatus($webmention, $http_code, $code, $raw=null) {
     $status = ORM::for_table('webmention_status')->create();
     $status->webmention_id = $webmention->id;