ASP.NET Core gRPC–Unary RPC vs Streams

When creating your gRPC implementation you have to be aware about the difference between Unary RPC and Streams.

Unary RPC

This is the simplest type of RPC, where the client sends a single request and gets back a single response. This is the simplest approach and similar to what we know when using WCF.

Streams

With streaming we have to make a difference between server streaming, client streaming and bidirectional streaming.

A server-streaming RPC is most similar to the Unary RPC, the only difference is that the server sends back a stream of responses instead of a single response after getting the client’s request message. After sending back all its responses, the server’s status details (status code and optional status message) and optional trailing metadata are sent back to complete on the server side. The client completes once it has all the server’s responses.

A client-streaming RPC turns things around, the client sends a stream of requests to the server instead of a single request. The server sends back a single response, typically but not necessarily after it has received all the client’s requests, along with its status details and optional trailing metadata.

In a bidirectional streaming RPC, the call is initiated by the client calling the method and the server receiving the client metadata, method name, and deadline. The server can choose to send back its initial metadata or wait for the client to start sending requests. What happens next depends on the application, as the client and server can read and write in any order - the streams operate completely independently.

It is important that you are aware of the difference as it can greatly impact the performance characteristics of your application. Working with streams can help you reduce the memory footprint of your application as you don’t have to buffer the whole response in memory before returning it to the client. Another advantage is that the client can start processing before all data is returned from the server(or the other way around).

More information: https://grpc.io/docs/guides/concepts/

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