Upgrade package:postgres and use a local socket file to communicate with the dev server.

app/lib/database/database.dart

@@ -100,14 +100,21 @@ Future<(String, String?)> _startOrUseLocalPostgresInDocker() async {
     throw StateError('Missing connection URL in Appengine environment.');
   }
 
+  final socketFile = File('/tmp/pub_dev_postgres/run/.s.PGSQL.5432');
+
   // the default connection URL for local server
   final url = Uri(
     scheme: 'postgresql',
-    host: 'localhost',
-    port: 55432,
     path: 'postgres',
     userInfo: 'postgres:postgres',
-    queryParameters: {'sslmode': 'disable'},
+    queryParameters: {
+      // If the socket file is present, let's try to use it, otherwise connect through the port.
+      // Both has benefits:
+      // - (during startup) calling the port is a blocking call and waits until the service is started,
+      // - (while the service is running) the socket file seems to provide a bit faster connection.
+      'host': await socketFile.exists() ? socketFile.path : 'localhost:55432',
+      'sslmode': 'disable',
+    },
   ).toString();
 
   try {
@@ -122,6 +129,9 @@ Future<(String, String?)> _startOrUseLocalPostgresInDocker() async {
         'Unexpect exit code from tool/start-local-postgres.sh\n${pr.stderr}',
       );
     }
+    // The socket file may be present sooner than the server is accepting connections.
+    // This arbitrary wait is probably enough to have a working server at this point.
+    await Future.delayed(Duration(seconds: 2));
   }
   return (url, null);
 }

app/pubspec.yaml

@@ -49,7 +49,7 @@ dependencies:
   pana: '0.23.0'
   # 3rd-party packages with pinned versions
   mailer: '6.5.0'
-  postgres: '3.5.8'
+  postgres: '3.5.9'
   ulid: '2.0.1'
   tar: '2.0.0'
   api_builder:

pubspec.lock

@@ -661,10 +661,10 @@ packages:
     dependency: transitive
     description:
       name: postgres
-      sha256: "96d7f40e079b96cdbfed13d71c64668cfd79c35bc17223c6b3ac0ca63bff72f0"
+      sha256: fefbbfe749c6130e5096588b9c4459173684c695952cd7636ab19be76f255469
       url: "https://pub.dev"
     source: hosted
-    version: "3.5.8"
+    version: "3.5.9"
   protobuf:
     dependency: transitive
     description: