(golang) Stream cancellation behavior?

[Scott Devoid]

Hi,

I have a few questions about how gRPC cancellation works in Golang:

First, what are the conditions under which a request could be
cancelled? I can think of a two but let me know if I am missing some
or incorrect:

- client cancels context.Context passed into request.
- TCP socket closes after a timeout?
- HTTP/2 client/server sends RST_STREAM for...reasons?

Second, if the client cancels the context, is the server notified
about this (assuming no loss of connectivity)? Can I select on
req.Context().Done() and perform some clean-up work after the fact or
does the request handler immediately return?

Third, in one of our bidirectional gRPC methods[1] we see a 'stream
error: code = 1 desc = "context cancelled"' event. However the client
passed in a context.Background() to the request so as far as I can
tell this cancellation has to be happening in grpc internals some
place. Does anyone know what is going on here?

Thanks!

~ Scott Devoid

[1] rpc Foo(stream Req) returns (stream Resp) {}

[Scott Devoid]

Any advice here would be appreciated.

Thanks,
~ Scott Devoid

[Qi Zhao]

On Mon, Jun 6, 2016 at 2:59 PM, Scott Devoid <sde...@gmail.com> wrote:

Hi,

I have a few questions about how gRPC cancellation works in Golang:

First, what are the conditions under which a request could be
cancelled? I can think of a two but let me know if I am missing some
or incorrect:

- client cancels context.Context passed into request.
- TCP socket closes after a timeout?
- HTTP/2 client/server sends RST_STREAM for...reasons?

The 1st and 3rd are the reasons. the 2nd won't cause a cancellation error. 

Second, if the client cancels the context, is the server notified
about this (assuming no loss of connectivity)? Can I select on
req.Context().Done() and perform some clean-up work after the fact or
does the request handler immediately return?

Yes, cancellation will propagate to the server if it is needed.  

Third, in one of our bidirectional gRPC methods[1] we see a 'stream
error: code = 1 desc = "context cancelled"' event. However the client
passed in a context.Background() to the request so as far as I can
tell this cancellation has to be happening in grpc internals some
place. Does anyone know what is going on here?

Not sure, perhaps the server initiated the cancellation. 

Thanks!

~ Scott Devoid

[1] rpc Foo(stream Req) returns (stream Resp) {}

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Thanks,

-Qi