Improve error handling for serving static DevTools assets.

Change-Id: I2b62461a64ef6aa8b544b4ace894d7b5ded0912e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/343000
Reviewed-by: Derek Xu <derekx@google.com>
Commit-Queue: Kenzie Davisson <kenzieschmoll@google.com>

pkg/dds/CHANGELOG.md

@@ -1,3 +1,7 @@
+# 3.1.2
+- Improved error handling for serving static DevTools assets.
+- Updated `devtools_shared` constraint to ^6.0.3.
+
 # 3.1.1
 - Updated `vm_service` constraint to ^14.0.0.
 

pkg/dds/README.md

@@ -37,3 +37,26 @@ void main() {
 
 [dds-protocol]: dds_protocol.md
 [service-protocol]: https://github.com/dart-lang/sdk/blob/main/runtime/vm/service/service.md
+
+# Debugging DDS
+
+One way to get stdout from files in DDS while debugging is to log messages to a file. You can add a method such as:
+
+```dart
+void _fileLog(String message) {
+  final file = File('/tmp/dds.log');
+  if (!file.existsSync()) {
+    file.createSync();
+  }
+  file.writeAsStringSync(
+'''
+$message
+''',
+    mode: FileMode.append,
+  );
+}
+```
+
+Then you can call `_fileLog('some print debugging message')`, and the log message will be written to a temp file.
+
+To get logging output in real time, run `tail -f /tmp/dds.log`.

pkg/dds/lib/src/devtools/handler.dart

@@ -71,11 +71,12 @@ FutureOr<Handler> defaultHandler({
           path.joinAll(pathSegments),
         );
         final contentType = lookupMimeType(extensionAssetPath) ?? 'text/html';
+        final baseHref = '$appRoot$extensionRequestPath/$extensionName/';
         return _serveStaticFile(
           request,
           File(extensionAssetPath),
           contentType,
-          baseHref: '$appRoot$extensionRequestPath/$extensionName/',
+          baseHref: baseHref,
         );
       }
     }
@@ -174,12 +175,22 @@ Future<Response> _serveStaticFile(
       // between a static file being served and accessed. See
       // https://github.com/flutter/devtools/issues/6365.
       await Future.delayed(Duration(milliseconds: 500));
-      fileBytes = file.readAsBytesSync();
+      try {
+        fileBytes = file.readAsBytesSync();
+      } catch (e) {
+        return Response.notFound('could not read file as bytes: ${file.path}');
+      }
     }
     return Response.ok(fileBytes, headers: headers);
   }
 
-  var contents = file.readAsStringSync();
+  late String contents;
+  try {
+    contents = file.readAsStringSync();
+  } catch (e) {
+    return Response.notFound('could not read file as String: ${file.path}');
+  }
+
   if (baseHref != null) {
     assert(baseHref.startsWith('/'));
     assert(baseHref.endsWith('/'));

pkg/dds/pubspec.yaml

@@ -1,5 +1,5 @@
 name: dds
-version: 3.1.1
+version: 3.1.2
 description: >-
   A library used to spawn the Dart Developer Service, used to communicate with
   a Dart VM Service instance.