Cannot catch SocketException thrown when sending GRPC request

[engelen]

When my GRPC server is unavailable, a SocketException is thrown in the http2_connection.dart file when I make a GRPC call; I appear to be unable to catch the error.

grpc-dart: 2.7.0

Repro steps

1. Start the GRPC server
2. Open a client channel
3. Start a client
4. Stop the GRPC server
5. Run a GRPC call

import 'package:grpc/grpc.dart';

import 'package:mypackage/api/v1/myservice.pbgrpc.dart' as grpc;

var channel = ClientChannel(
  serverIP,
  port: serverPort,
  options: ChannelOptions(
    credentials: ChannelCredentials.insecure(),
    idleTimeout: Duration(seconds: 10),
  ),
);

var client = grpc.MyClient(channel);

client.myCall().then((response) {
  print('success');
}, onError: (error) {
  print('onError');
}).catchError((error) {
  print('catchError');
});

Expected result: printing 'onError'

Actual result:

Exception has occurred.
SocketException (SocketException: OS Error: Connection refused, errno = 111, address = 10.0.2.2, port = 43316)

on this line:

grpc-dart/lib/src/client/http2_connection.dart

Line 311 in 5b3a125

_socket = await Socket.connect(_host, _port);

Thanks for your help!

[mraleph]

I don't seem to be able to reproduce this. I see error correctly propagate. I have tried reproducing this using helloworld example doing two different things:

• Run client without server. Got

  Caught error: gRPC Error (code: 14, codeName: UNAVAILABLE, message: Error connecting: SocketException: OS Error: Connection refused, errno = 61, address = localhost, port = 62017, details: null)
  

• Add loop repeating the call every 10s and killed server after the first successful call. Got

  Greeter client received: Hello, world!
  Caught error: gRPC Error (code: 14, codeName: UNAVAILABLE, message: Error connecting: SocketException: OS Error: Connection refused, errno = 61, address = localhost, port = 62066, details: null)
  

Could you provide the full runnable reproduction for the problem?

[engelen]

@mraleph Thanks a lot for your help. I'm sorry for not responding earlier; it turns out I had email notifications turned off.

I've downloaded the hello world example and tried to reproduce it, and it turns out the issue does not occur when I run dart from the command line directly, but it does occur when I run dart using VS code. In VS Code, if I untick the checkbox Uncaught Exceptions in the Breakpoints settings screen, the problem does not occur anymore, and the error is nicely caught. (if the checkbox is ticked, I get the problem I described in the issue description)

It seems like VS Code is marking this as an "Uncaught exception", although it is clearly caught. Could this issue be due to the way grpc-dart handles errors, or should I contact VS Code?

[engelen]

It looks a problem in VS Code / Dart itself:
flutter/flutter#33427
Dart-Code/Dart-Code#2063

[mraleph]

Thanks for the context! I would imagine that even when "Uncaught Exceptions" check box is ticked you should be able to resume execution - after which exception should be caught in the right place.

I have pinged dart-lang/sdk#37953 (which is the upstream Dart bug tracking improvements in "pause on unhandled exceptions" functionality). Let's see what we can do about it.

[engelen]

Excellent, thanks a lot!