What is the behaviour of grpc::ServerContext::IsCancelled()

[Okke Hendriks]

Hello,

I am using the sync grpc C++ API v1.10.0.

Could someone explain to me what the exact behaviour of IsCancelled() is?

Does it evaluate to true if and only if the client sends a TryCancel() which was received by the server? 

Or also if a call/stream closed due to another reason (socket closed, OS error, etc.)?

If it is NOT the case that it only returns true when a client cancelled, is there a way to find the reason of the cancellation, aka the status?

Kind regards,

Okke Hendriks

[ncte...@google.com]

Taking a look at the C API, it looks like IsCancelled() will be true "if the call failed in any way". See here.

There is not an API method to determine more info about error, but that should be available by examining logs. (setting GRPC_VERBOSITY=debug and GRPC_TRACE=all)

[Okke Hendriks]

Thank you,

Indeed it seems to be the case that it is more like IsFailed() instead of IsCanceled().

If i examine the grpc_call struct, (accessible through the c++ API, but using it will require including non-public core lib headers? Which i do not want to do.) it has an grpc_call_final_info member defined here. 

Which includes a grpc_status_code  and error message, I do not know if these are set on the server side, but this might be something to expose on the C/C++ API?

[Noah Eisen]

Can you give a little more info about your use case? What exact information do you need, and in what situations?

I agree that digging into the non-public structs is a bad idea, since we maybe change those from time to time. If you present a use case that is lacking from our public API, we can add some new methods to ServerContext to expose more details

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[Okke Hendriks]

Our use case was that we had a RPC call 'FollowPath'.

This call instructs a robot to, you guessed it, follow a path. In case a client does a TryCancel() on the 'FollowPath' the robot must stop following the previously given path.

In case the WiFi connection fails and the RPC is 'aborted' the robot must continue following the path it was given.

So basically we want to know the difference between a failed call/stream and an actively canceled (by the client) call/stream.