Flutter iOS: Connection was disconnected after changing network state between wifi <> cellular (grpc-dart - version 3.0.2)

[ThanhDat-Vo]

Stream stops receiving messages after changing network state

grpc-dart version: 3.0.2

Repro steps

1. start the unary grpc request from Flutter iOS app
2. switching between wifi <> cellular
3. the request was hang forever

Expected result: connection should be kept after changing network state

Actual result: connection was disconnect. After long period of time, an UNAVAILABLE grpc error code returned.

Related problems:

• Stream stops receiving messages after changing connection from Wifi to Cellular grpc-swift#337
• https://grpc.github.io/grpc/objc/md_src_objective-c__network_transition_behavior.html

Please help!

Thanks

[mraleph]

By default grpc-dart uses package:http2 which uses dart:io underneath which uses BSD sockets, so the behaviour you are seeing is expected.

Right now the best solution you can come up with is to implement some code on the side to monitor network state changes and manually drop old connection and reconnect when network state changes.

As noted in the linked doc a possible solution to this problem would be to connect over CFStream - but currently we don't have a networking stack implementation that could do it. /cc @brianquinlan