Client error message

Summary:
See previous diff in stack for context, serialization can fail and when it does we just send an empty string payload to flipper which is v confusing.

Instead we now do proper error handling

A note about the use of try catch around nsjson serialization i know this is not typical but the previous approach was to use the validator function to see if data could be serialized. this was returning false before but the problem is we have idea what the error is. Unfortunatley despite taking an error parm the NSJSONSerialization dataWithJSONObject function throws an exception so im force to catch it to get a useful error message

Differential Revision: D65605276

fbshipit-source-id: 506ecc48bd0692a622679a8f621fede7d626c122

Author: Luke De Feo

iOS/Plugins/FlipperKitUIDebuggerPlugin/FlipperKitUIDebuggerPlugin/Observer/UIDTreeObserverManager.m

@@ -207,7 +207,37 @@ - (void)sendInit {
   init.frameworkEventMetadata = [_context.frameworkEventManager eventsMetadata];
   init.currentTraversalMode = _traversalMode;
 
-  [_context.connection send:[UIDInitEvent name] withRawParams:UID_toJSON(init)];
+  NSError* error = nil;
+  if (error) {
+    [self sendClientErrorMessage:error step:@"init"];
+    return;
+  }
+  [_context.connection send:[UIDInitEvent name]
+              withRawParams:UID_toJSON(init, &error)];
+}
+
+- (void)sendClientErrorMessage:(NSError*)error step:(NSString*)step {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnullable-to-nonnull-conversion"
+
+  NSDictionary* clientError = @{
+    @"errorMessage" : error.localizedDescription,
+    @"errorType" : error.localizedFailureReason,
+    @"step" : step,
+  };
+
+  NSError* errorMessageSerializeError = nil;
+  NSString* clientErrorEvent =
+      UID_FoundationtoJSON(clientError, &errorMessageSerializeError);
+
+  if (errorMessageSerializeError) {
+    // uh oh...
+    return;
+  }
+
+  [_context.connection send:@"traversalError" withRawParams:clientErrorEvent];
+
+#pragma clang diagnostic pop
 }
 
 - (void)sendMetadataUpdate {
@@ -220,7 +250,12 @@ - (void)sendMetadataUpdate {
   UIDMetadataUpdateEvent* metadataUpdateEvent = [UIDMetadataUpdateEvent new];
   metadataUpdateEvent.attributeMetadata = pendingMetadata;
 
-  id JSON = UID_toJSON(metadataUpdateEvent);
+  NSError* error = nil;
+  id JSON = UID_toJSON(metadataUpdateEvent, &error);
+  if (error) {
+    [self sendClientErrorMessage:error step:@"metadataUpdate"];
+    return;
+  }
 
   [_context.connection send:[UIDMetadataUpdateEvent name] withRawParams:JSON];
 }
@@ -252,7 +287,14 @@ - (void)digest:(nonnull id<UIDUpdate>)update {
 
     uint64_t t3 = UIDPerformanceNow();
 
-    NSString* JSON = UID_FoundationtoJSON(intermediate);
+    NSError* error = nil;
+
+    NSString* JSON = UID_FoundationtoJSON(intermediate, &error);
+    if (error) {
+      [self sendClientErrorMessage:error step:@"serialization"];
+      return;
+    }
+
     uint64_t t4 = UIDPerformanceNow();
     NSUInteger payloadSize = JSON.length;
 
@@ -280,8 +322,12 @@ - (void)digest:(nonnull id<UIDUpdate>)update {
     perfStats.payloadSize = payloadSize;
     perfStats.dynamicMeasures = UIDPerformanceGet();
 
+    NSString* perfStatsMessage = UID_toJSON(perfStats, &error);
+    if (error) {
+      [self sendClientErrorMessage:error step:@"perfStats"];
+    }
     [self->_context.connection send:[UIDPerfStatsEvent name]
-                      withRawParams:UID_toJSON(perfStats)];
+                      withRawParams:perfStatsMessage];
   });
 }
 

iOS/Plugins/FlipperKitUIDebuggerPlugin/FlipperKitUIDebuggerPlugin/Serializers/UIDJSONSerializer.h

@@ -17,8 +17,8 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-extern NSString* UID_toJSON(id obj);
-extern NSString* UID_FoundationtoJSON(id obj);
+extern NSString* UID_toJSON(id obj, NSError** error);
+extern NSString* UID_FoundationtoJSON(id obj, NSError** error);
 extern id UID_toFoundation(id<UIDFoundation> obj);
 #ifdef __cplusplus
 }

iOS/Plugins/FlipperKitUIDebuggerPlugin/FlipperKitUIDebuggerPlugin/Serializers/UIDJSONSerializer.mm

@@ -30,37 +30,55 @@
 id UID_toFoundation(id<UIDFoundation> object) {
   return [object toFoundation];
 }
+NSString* UID_FoundationtoJSON(id object, NSError** error) {
+  uint64_t t0 = UIDPerformanceNow();
 
-NSString* UID_FoundationtoJSON(id object) {
-  NSError* error = NULL;
-  if (![NSJSONSerialization isValidJSONObject:object]) {
-    return @"";
-  }
+  // NSJSONSerialization dataWithJSONObject throws and exception if data not
+  // serializable despite taking an error param hence the try catch
+  @try {
+    uint64_t t1 = UIDPerformanceNow();
 
-  uint64_t t0 = UIDPerformanceNow();
+    NSData* data = [NSJSONSerialization dataWithJSONObject:object
+                                                   options:0
+                                                     error:error];
+
+    if (*error) {
+      return nil;
+    }
 
-  NSData* data = [NSJSONSerialization dataWithJSONObject:object
-                                                 options:0
-                                                   error:&error];
-  uint64_t t1 = UIDPerformanceNow();
+    UIDPerformanceAggregate(
+        @"serialisationBinaryMS",
+        UIDMonotonicTimeConvertMachUnitsToMS(t1 - t0));
 
-  UIDPerformanceAggregate(
-      @"serialisationBinaryMS", UIDMonotonicTimeConvertMachUnitsToMS(t1 - t0));
+    NSString* JSON = [[NSString alloc] initWithData:data
+                                           encoding:NSUTF8StringEncoding];
 
-  NSString* JSON = [[NSString alloc] initWithData:data
-                                         encoding:NSUTF8StringEncoding];
+    uint64_t t2 = UIDPerformanceNow();
 
-  uint64_t t2 = UIDPerformanceNow();
+    UIDPerformanceAggregate(
+        @"serialisationEncodingMS",
+        UIDMonotonicTimeConvertMachUnitsToMS(t2 - t1));
 
-  UIDPerformanceAggregate(
-      @"serialisationEncodingMS",
-      UIDMonotonicTimeConvertMachUnitsToMS(t2 - t1));
+    return JSON;
 
-  return JSON;
+  } @catch (NSException* exception) {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnullable-to-nonnull-conversion"
+    *error = [NSError errorWithDomain:@"com.facebook.flipper.uidebugger"
+                                 code:100
+                             userInfo:@{
+                               NSLocalizedDescriptionKey : exception.reason,
+                               NSLocalizedFailureReasonErrorKey : exception.name
+                             }];
+
+    return nil;
+
+#pragma clang diagnostic pop
+  }
 }
 
-NSString* UID_toJSON(id object) {
-  return UID_FoundationtoJSON(UID_toFoundation(object));
+NSString* UID_toJSON(id object, NSError** error) {
+  return UID_FoundationtoJSON(UID_toFoundation(object), error);
 }
 #ifdef __cplusplus
 }