Add a stackFrameFilter argument to SentryClient's capture (#30)

This allows filtering sensitive frames on the client or applying
custom truncation logic.

Author: tom95

lib/sentry.dart

@@ -164,7 +164,8 @@ class SentryClient {
       '${dsnUri.scheme}://${dsnUri.host}/api/$projectId/store/';
 
   /// Reports an [event] to Sentry.io.
-  Future<SentryResponse> capture({@required Event event}) async {
+  Future<SentryResponse> capture(
+      {@required Event event, StackFrameFilter stackFrameFilter}) async {
     final DateTime now = _clock();
     String authHeader = 'Sentry sentry_version=6, sentry_client=$sentryClient, '
         'sentry_timestamp=${now.millisecondsSinceEpoch}, sentry_key=$publicKey';
@@ -192,7 +193,8 @@ class SentryClient {
     if (userContext != null) {
       mergeAttributes({'user': userContext.toJson()}, into: data);
     }
-    mergeAttributes(event.toJson(), into: data);
+    mergeAttributes(event.toJson(stackFrameFilter: stackFrameFilter),
+        into: data);
 
     List<int> body = utf8.encode(json.encode(data));
     if (compressPayload) {
@@ -216,15 +218,19 @@ class SentryClient {
   }
 
   /// Reports the [exception] and optionally its [stackTrace] to Sentry.io.
+  ///
+  /// Optionally allows specifying a [stackFrameFilter] that receives the
+  /// list of stack frames just before sending to allow modifying it.
   Future<SentryResponse> captureException({
     @required dynamic exception,
     dynamic stackTrace,
+    StackFrameFilter stackFrameFilter,
   }) {
     final Event event = new Event(
       exception: exception,
       stackTrace: stackTrace,
     );
-    return capture(event: event);
+    return capture(event: event, stackFrameFilter: stackFrameFilter);
   }
 
   Future<Null> close() async {
@@ -376,7 +382,7 @@ class Event {
   final List<String> fingerprint;
 
   /// Serializes this event to JSON.
-  Map<String, dynamic> toJson() {
+  Map<String, dynamic> toJson({StackFrameFilter stackFrameFilter}) {
     final Map<String, dynamic> json = <String, dynamic>{
       'platform': sdkPlatform,
       'sdk': {
@@ -406,7 +412,8 @@ class Event {
 
     if (stackTrace != null) {
       json['stacktrace'] = <String, dynamic>{
-        'frames': encodeStackTrace(stackTrace),
+        'frames':
+            encodeStackTrace(stackTrace, stackFrameFilter: stackFrameFilter),
       };
     }
 

lib/src/stack_trace.dart

@@ -4,6 +4,11 @@
 
 import 'package:stack_trace/stack_trace.dart';
 
+/// Used to filter or modify stack frames before sending stack trace. The stack
+/// frames are in the Sentry.io format.
+typedef StackFrameFilter = List<Map<String, dynamic>> Function(
+    List<Map<String, dynamic>>);
+
 /// Sentry.io JSON encoding of a stack frame for the asynchronous suspension,
 /// which is the gap between asynchronous calls.
 const Map<String, dynamic> asynchronousGapFrameJson = const <String, dynamic>{
@@ -13,7 +18,8 @@ const Map<String, dynamic> asynchronousGapFrameJson = const <String, dynamic>{
 /// Encodes [stackTrace] as JSON in the Sentry.io format.
 ///
 /// [stackTrace] must be [String] or [StackTrace].
-List<Map<String, dynamic>> encodeStackTrace(dynamic stackTrace) {
+List<Map<String, dynamic>> encodeStackTrace(dynamic stackTrace,
+    {StackFrameFilter stackFrameFilter}) {
   assert(stackTrace is String || stackTrace is StackTrace);
   final Chain chain = stackTrace is StackTrace
       ? new Chain.forTrace(stackTrace)
@@ -24,7 +30,9 @@ List<Map<String, dynamic>> encodeStackTrace(dynamic stackTrace) {
     frames.addAll(chain.traces[t].frames.map(encodeStackTraceFrame));
     if (t < chain.traces.length - 1) frames.add(asynchronousGapFrameJson);
   }
-  return frames.reversed.toList();
+
+  final jsonFrames = frames.reversed.toList();
+  return stackFrameFilter != null ? stackFrameFilter(jsonFrames) : jsonFrames;
 }
 
 Map<String, dynamic> encodeStackTraceFrame(Frame frame) {

test/stack_trace_test.dart

@@ -74,5 +74,23 @@ void main() {
         },
       ]);
     });
+
+    test('allows changing the stack frame list before sending', () {
+      StackFrameFilter filter =
+          (list) => list.where((f) => f['abs_path'] != 'secret.dart').toList();
+
+      expect(encodeStackTrace('''
+#0      baz (file:///pathto/test.dart:50:3)
+#1      bar (file:///pathto/secret.dart:46:9)
+      ''', stackFrameFilter: filter), [
+        {
+          'abs_path': 'test.dart',
+          'function': 'baz',
+          'lineno': 50,
+          'in_app': true,
+          'filename': 'test.dart'
+        },
+      ]);
+    });
   });
 }