Limit log output

Author: gspencergoog

pkgs/dart_mcp_server/lib/src/mixins/flutter_launcher.dart

@@ -8,6 +8,7 @@ library;
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
+import 'dart:math' as math;
 
 import 'package:dart_mcp/server.dart';
 
@@ -171,10 +172,15 @@ base mixin FlutterLauncherSupport
             'Flutter application ${process!.pid} exited with code $exitCode.',
           );
           if (!completer.isCompleted) {
-            final logOutput = _runningApps[process.pid]?.logs.join('\n');
+            final logs = _runningApps[process.pid]?.logs ?? [];
+            // Only output the last 500 lines of logs.
+            final startPos = math.max(0, logs.length - 500);
+            final logOutput = logs.sublist(startPos).join('\n');
             completer.completeError(
               'Flutter application exited with code $exitCode before the DTD '
-              'URI was found, with log output:\n$logOutput',
+              'URI was found, with log output:\n'
+              '''${startPos > 0 ? '[showing only the last 500 lines of a log with ${logs.length} lines]...' : ''}'''
+              '$logOutput',
             );
           }
           _runningApps.remove(process.pid);
@@ -362,6 +368,11 @@ base mixin FlutterLauncherSupport
               'The process ID of the flutter run process running the '
               'application.',
         ),
+        'maxLines': Schema.int(
+          description:
+              'The maximum number of log lines to return from the end of the '
+              'logs. Defaults to 500. If set to -1, all logs will be returned.',
+        ),
       },
       required: ['pid'],
     ),
@@ -378,8 +389,9 @@ base mixin FlutterLauncherSupport
 
   Future<CallToolResult> _getAppLogs(CallToolRequest request) async {
     final pid = request.arguments!['pid'] as int;
+    var maxLines = request.arguments!['maxLines'] as int? ?? 500;
     log(LoggingLevel.info, 'Getting logs for application with PID: $pid');
-    final logs = _runningApps[pid]?.logs;
+    var logs = _runningApps[pid]?.logs;
 
     if (logs == null) {
       log(
@@ -396,6 +408,17 @@ base mixin FlutterLauncherSupport
       );
     }
 
+    if (maxLines == -1) {
+      maxLines = logs.length;
+    }
+    if (maxLines > 0 && maxLines <= logs.length) {
+      final startLine = logs.length - maxLines;
+      logs = [
+        if (startLine > 0) '[skipping $startLine log lines]...',
+        ...logs.sublist(startLine),
+      ];
+    }
+
     return CallToolResult(
       content: [TextContent(text: logs.join('\n'))],
       structuredContent: {'logs': logs},

pkgs/dart_mcp_server/test/tools/flutter_launcher_test.dart

@@ -337,6 +337,83 @@ void main() {
       await client.shutdown();
     });
 
+    test.test('get_app_logs tool respects maxLines', () async {
+      final dtdUri = 'ws://127.0.0.1:12345/abcdefg=';
+      final processPid = 54321;
+      final mockProcessManager = MockProcessManager();
+      mockProcessManager.addCommand(
+        Command(
+          [
+            Platform.isWindows
+                ? r'C:\path\to\flutter\sdk\bin\cache\dart-sdk\bin\dart.exe'
+                : '/path/to/flutter/sdk/bin/cache/dart-sdk/bin/dart',
+            'language-server',
+            '--protocol',
+            'lsp',
+          ],
+          stdout:
+              '''Content-Length: 145\r\n\r\n{"jsonrpc":"2.0","id":0,"result":{"capabilities":{"workspace":{"workspaceFolders":{"supported":true,"changeNotifications":true}},"workspaceSymbolProvider":true}}}''',
+        ),
+      );
+      mockProcessManager.addCommand(
+        Command(
+          [
+            Platform.isWindows
+                ? r'C:\path\to\flutter\sdk\bin\flutter.bat'
+                : '/path/to/flutter/sdk/bin/flutter',
+            'run',
+            '--print-dtd',
+            '--device-id',
+            'test-device',
+          ],
+          stdout:
+              'line 1\nline 2\nline 3\n'
+              'The Dart Tooling Daemon is available at: $dtdUri\n',
+          pid: processPid,
+        ),
+      );
+      final serverAndClient = await createServerAndClient(
+        processManager: mockProcessManager,
+        fileSystem: fileSystem,
+      );
+      final server = serverAndClient.server;
+      final client = serverAndClient.client;
+
+      // Initialize and launch the app
+      await client.initialize(
+        InitializeRequest(
+          protocolVersion: ProtocolVersion.latestSupported,
+          capabilities: ClientCapabilities(),
+          clientInfo: Implementation(name: 'test_client', version: '1.0.0'),
+        ),
+      );
+      client.notifyInitialized();
+      await client.callTool(
+        CallToolRequest(
+          name: 'launch_app',
+          arguments: {'root': projectRoot, 'device': 'test-device'},
+        ),
+      );
+
+      // Get the logs
+      final result = await client.callTool(
+        CallToolRequest(
+          name: 'get_app_logs',
+          arguments: {'pid': processPid, 'maxLines': 2},
+        ),
+      );
+
+      test.expect(result.isError, test.isNot(true));
+      test.expect(result.structuredContent, {
+        'logs': [
+          '[stdout] line 3',
+          '[stdout] The Dart Tooling Daemon is available at: $dtdUri',
+        ],
+      });
+      await server.shutdown();
+      await client.shutdown();
+    });
+
     test.test('list_devices tool returns available devices', () async {
       final mockProcessManager = MockProcessManager();
       mockProcessManager.addCommand(