bidirectional communication on the same socket?

[dan.b...@huawei.com]

Once establishing a connection from one service (behind a firewall) to another service, 

is it correct that gRPC can now use the established connection to initiate requests on either side?

If there's a pointer to some example demonstrating such bidirectional communication that would be great.

Thanks,

Dan

[robert engels]

If you mean using the ‘streaming’ protocol, you can look at github.com/robaho/keydbr which uses a bi-directional stream and the code is fairly simple.

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[dan.b...@huawei.com]

Not necessarily for streaming. For sending requests and receiving synchronous or asynchronous responses. (unless I completely misunderstand what streaming means)

[robert engels]

It is my understanding - but I may be mistaken here - is that a gRPC “session” is uni directional unless you use streaming (that being said, a server can send unsolicited “responses” - which may be treated like a request to the client- to a client).

My continued confusion is that I believe the standard gRPC session is transient - in that it may close the connection after each request - and it may send a subsequent request to a completely different server, or on a new connection. The only time this is not the case is if the session is in streaming mode.

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[Srini Polavarapu]

I think the OP is asking if server can start a request to client after client (behind a firewall) has established a gRPC connection to the server. The answer is no. See discussion here https://github.com/grpc/grpc/issues/14101. It is possible in gRPC-Go in a convoluted way. See https://github.com/grpc/grpc-go/issues/484

[dan.b...@huawei.com]

This is exactly what I meant, and I understand that the answer.

Is it possible to open two sockets (from behind the firewall to a public IP) and establish one of them as a gRPC connection from behind the firewall out, and the other as a gRPC from the outside into the firewalled system?

(e.g. client->server client<-server)