allow configuring the local port ditto listens on

src/config.ts

@@ -39,6 +39,11 @@ class Conf {
       ['sign', 'verify'],
     );
   }
+
+  static get localPort() {
+    return parseInt(Deno.env.get('DITTO_LISTEN_ON') || '8000');
+  }
+
   static get relay(): `wss://${string}` | `ws://${string}` {
     const { protocol, host } = Conf.url;
     return `${protocol === 'https:' ? 'wss:' : 'ws:'}//${host}/relay`;

src/server.ts

@@ -1,5 +1,6 @@
 import '@/precheck.ts';
 import '@/sentry.ts';
 import app from '@/app.ts';
+import { Conf } from '@/config.ts';
 
-Deno.serve(app.fetch);
+Deno.serve({ port: Conf.localPort }, app.fetch);