using grpc for push notification

[Chaitanya Gangwar]

Hi,

I have a requirement, where  multiple clients send (register) a request to server and continue, whenever server have data, server will push the data to clients. it may be possible that server may not have data at present and will keep pushing data whenever it has. Some other thread is providing the data to server.

Can i do this with grpc without blocking the server and client. What i understand from grpc streaming is that client will be waiting for data till server sends out the data and after receiving the data it closes the connection.

please help, if i can do this using grpc and if yes how should i design this.

thanks
Chaitanya

[Josh Humphries]

This is a straight-forward streaming-response style endpoint in GRPC. (Use the "stream" keyword for the response when defining this method in a proto source file.)

The client doesn't necessarily "wait for" data. It receives it asynchronously. A streaming response means that the server can send zero or more messages in reply to the request.

The RPC can remain active for the entire duration that the client is connected, and the server can use the response stream (once initiated by a client -- via the initial request) to send data, as it comes in.

----

Josh Humphries

Manager, Shared Systems  |  Platform Engineering

Atlanta, GA  |  678-400-4867

Square (www.squareup.com)

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[Chaitanya Gangwar]

Thanks josh for the reply. So for this case i need both async server and client. sync rpc will not work. please correct me if i am wrong. also do we have any example which i can look into. i checked async helloworld but that is simple rpc do we have any example for async stream rpc.

[Josh Humphries]

There is an example of streaming, at least in a proto file:

https://github.com/grpc/grpc/blob/master/examples/protos/hellostreamingworld.proto

In this case, the server is expected to just immediately send the requested number of messages.

Assuming you had some "registry" of streams that represent clients to which you forward data:

In your server implementation, you'd just register the StreamObserver (that's what its called in the Java runtime anyway).

Here's example generated code for an endpoint with a streaming response: https://github.com/grpc/grpc-java/blob/master/examples/src/generated/main/grpc/io/grpc/examples/routeguide/RouteGuideGrpc.java#L80

(That's the interface you implement on the server.)

When your server receives data from whatever other source, it can consult this registry of streams and then call onNext to send the client(s) data. Unregister when the stream errors or when you close the stream. You close it via calling onComplete or onError (latter will send error code to the client).

----

Josh Humphries

Manager, Shared Systems  |  Platform Engineering

Atlanta, GA  |  678-400-4867

Square (www.squareup.com)

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[John Coffey]

Josh/Chaitanya, I have a similar application - are there any C++ examples that do this kind of thing?  I just posted a new question to the newsgroup asking and then I found this thread.

John

[chaitanya gangwar]

Hi John,

When i was working on this, there was no example in grpc package to do the same. Actually, what you need here is asynchronous streaming, but in examples, there are 2 variant, one is synchronous stream (routeguide) and normal async rpc (helloworld). You have to understand both the examples and need to implement async stream yourself. I may have some poc code with me where i tested this functionality. Ill check my repo and will post it to you. May be that will be of some help for you.

Thanks

Chaitanya

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[John Coffey]

Chaitanya, 

that would be really useful, thanks, I will look forward to seeing the code.  It is strange that gRPC does not have asynchronous stream support, you would think this kind of listener/observe pattern would be a pretty popular feature.

John

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[chaitanya gangwar]

Hi John,

I have added 2 variant of routeguide example, one for asyn stream with one rpc and other for async stream multiple rpc. You can take a look at the code. this was working with grpc 0_11 version. This will give you a good idea of how to use grpc for asyn stream.

https://drive.google.com/open?id=0B1MMqYKUHgtJQWN4cjB6U25LdTQ

Thanks

Chaitanya

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[pira...@gmail.com]

Hi Chaitanya,

Thank you for you sharing! Can you provide the .proto file with it? It's hard to understand without the .proto file, and I can't change the code and recompile it. 

Thanks

Sean

[chaitanya gangwar]

proto file is in same folder under proto directory.

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[pira...@gmail.com]

Hi Chaitanya,

There are two rar files inside the share, I can't find proto directory or files in both of them. please help me.

Thanks

Sean

[chaitanya gangwar]

Oh i think i missed the grpc proto file. But its the same as present in git repository example folder. This code is modification of example present in grpc source. You just need to make a small change, add "stream" keyword in return argument.

https://github.com/grpc/grpc/blob/master/examples/protos/route_guide.proto

-Chaitanya

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[pira...@gmail.com]

Get it! Thank you for your help. You are wonderful.

 

[rav...@gmail.com]

Hi Chaitanya,

Could you please share async stream code? 

The link seem to be broken now.

thanks.

[mscud...@googlemail.com]

Could you please repost the examples of th c++ async route guide demos,
Would be very helpful.

Thanks, Marco.

[Chaitanya Gangwar]

Hi All,

Previous files got deleted somehow. I am uploading it again. Please use this link :

https://drive.google.com/file/d/1jqviARRz5muVCdsBjw3WPH8xSSGpXrv1/view?usp=sharing

Thanks
Chaitanya

[jonatha...@gmail.com]

Hello everyone,

would anyone have an example in C#/.NET Core?

Thanks,

Jonathan