How do I respond to multiple gRPC clients?

4
votes

I am building an application which can have multiple gRPC servers and definitely will have multiple gRPC clients, I wanted to know, how to identify on server side that this is the client I am talking to and only send data to that client. I am using bidirectional streaming RPC and right now the data gets broadcasted to every client and I don't want that. What functions in go gRPC make it possible or how can I implement it?

2
godistributed-computinggrpcgrpc-go
you want a stream client interceptor, and google.golang.org/grpc/metadata. This way you can intercept each call and check it's identity based on whatever flow (I agree with the answer, JWT is a nice option) – Robbie Milejczak

2 Answers

1
votes

There are two ways to read this question. One way is to read it as the auth problem as answered before. The second way is how I read it, as a connection/session problem.

When the client connects, the grpc server will invoke a function to implement the call in its own goroutine, and that function will be only talking to the client that initiated that call. So, the struct you registered as your grpc server will be shared among many connections, but each connection will run in its own goroutine, and will only talk to the client that initiated it. That also means you have to make sure the grpc server implementation is thread-safe.

You mentioned data is being broadcasted to every client? There is no broadcast in grpc, are you sure that's what's happening?

0
votes

This sounds like a common authentication/authorization problem that ultimately won't have much to do with gRPC or Go.

You need a way for a client to indicate who they are. Personally I'm a fan of JWTs. In a standard HTTP request, there are authorization headers that can indicate who is making the request. Similarly, gRPC supports meta data attached to each remote call. In my current work project, every call must have a JWT in the meta data or else I don't process the request. Every call except the login endpoint that is.

I haven't looked into how to get details like a gRPC client's IP address or other information about a client's connection but chances are that anything provided by gRPC's generated code is something potentially faked by the client. When architected correctly, JWTs can offer cryptographic confidence that the client is who they claim to be.