When remote debugging is turned on, underlying error in promise rejection causes: NSError RCTJSONStringify: Invalid type in JSON write (NSError)

[neilsarkar]

Issue Description

Some native modules such as NSFileManager return an NSError that has an underlying NSError in the userInfo dictionary. React native handles this fine out of the box, but when the remote debugger is turned on, the websocket message sender chokes on attempting to stringify the second NSError into json.

I'm happy to help fix this, first time contributing so any pointers are welcome.

Steps to Reproduce / Code Snippets

I've posted a repository with the minimal reproduction case here https://github.com/superseriouscompany/react-native-error-repro

The steps are: first, turn on remote debugging. Then implement the following code:

// objc
RCT_EXPORT_METHOD(triggerError:(NSString *)foo
                  resolver:(RCTPromiseResolveBlock)resolve
                  rejecter:(RCTPromiseRejectBlock)reject)
{
  NSError *underlyingError = [NSError errorWithDomain:@"underlyingDomain" code:419 userInfo:nil];
  NSError *err = [NSError errorWithDomain:@"domain" code:68 userInfo:@{@"NSUnderlyingError": underlyingError}];

  reject(@"foo", @"bar", err);
}

// js
triggerError('anything').catch(err => { console.log(err)})

Expected Results

error is logged to console, execution continues.

Actual Results

### Additional Information - React Native version: 0.35.0 - Platform(s) (iOS, Android, or both?): iOS - Operating System (macOS, Linux, or Windows?): macOS

[lacker]

By the way I really appreciate that you are just sending a pull request to fix this! So props for that.

[fungilation]

I'm still hitting a similar error:

RCTJSONStringify() encountered the following error: Invalid type in JSON write (NSURL)

With NSURL in brackets instead.

I haven't been hitting this error until I upgraded RN from 0.37 to 0.41.

[miklschmidt]

@fungilation until or since? Because i still have it on 0.41.2.

[fungilation]

Until. I've never seen it on 0.37 and older. But that could just have been me testing less before.

[miklschmidt]

Okay, in my case it seems to be the AppTransportSecurityPolicy (or whatever it's called) that wasn't set to allow insecure connections. I had to hack RTCUtils.m:82 to print the JSON blob instead of the error. It seems like the userInfo object is the cause of the issue.

[fungilation]

In my case, I've already set AppTransportSecurityPolicy allowed insecure connections.

[miklschmidt]

Try doing the same thing, the json blob will tell you what's wrong. It's a workaround for now at least.

[neilsarkar]

You can also disable Remote JS Debugging and read the logs from the XCode console in order to find out what the actual error is.

So I could write the same kind of patch for an NSError containing an NSURL that I did for an NSError containing an NSError, but that feels like playing a game of whack-a-mole...theoretically any object could be returned from an error and we would have to keep special casing in this function to serialize the error.

Anyone with a little more objective c knowledge have a suggestion for a way to generically stringify (or, worst case, strip) any type of object that could be attached to an error?

[neilsarkar]

I was unable to reproduce with the following test:

- (void)testEncodingNSURL
{
  NSURL *url = [[NSURL alloc] initWithString:@"https://www.facebook.com"];
  
  NSError *err = [NSError errorWithDomain:@"domain" code:68 userInfo:@{@"url": url}];
  
  // An assertion on the full object would be too brittle since it contains an iOS stack trace
  // so we are relying on the behavior of RCTJSONParse, which is tested below.
  NSDictionary<NSString *, id> *jsonObject = RCTJSErrorFromNSError(err);
  NSString *jsonString = RCTJSONStringify(jsonObject, NULL);
  NSDictionary<NSString *, id> *json = RCTJSONParse(jsonString, NULL);
  XCTAssertEqualObjects(json[@"code"], @"EDOMAIN68");
  XCTAssertEqualObjects(json[@"message"], @"The operation couldn\u2019t be completed. (domain error 68.)");
  XCTAssertEqualObjects(json[@"domain"], @"domain");
  XCTAssertEqualObjects(json[@"userInfo"][@"url"], @"https://www.facebook.com");
}

so it may be a new or different error. can anyone provide steps for reproduction?