Call Interceptor functionality

[adriantabirta]

On client side I need an interceptor, would be great if we do have one like in go

[glbrntt]

@adriantabirta what's your specific use case? It might be something we can solve without interceptors. I agree though, interceptors would be helpful!

[adriantabirta]

I would use Interceptors for:

• auth - (server side check auth token, client side to get a token/refresh)
• metrics - (server side)
• stream filter/validation - (probably most for server side)

[whilesoftware]

@glbrntt is this on the roadmap?

I'd love to take a stab at implementing it. I was thinking of creating a mechanism to specify additional ChannelHandlers per-Server and/or per-CallHandlerProvider to be injected into the Pipeline between GRPCServerRequestRoutingHandler and BaseCallHandler.

The API would look something like:

extension CallHandlerProvider {
  public var prefixedHandlers: [ChannelHandler.Type]? { get }
}

extension Server.Builder {
  @discardableResult
  public func withPrefixHandlers(_ handlers: [ChannelHandler.Type]) -> Self {
    // prefixedHandlers gets added to Server.Configuration
    self.prefixedHandlers = handlers
    return self
  }
}

Does that sound right?

This would work nicely for my needs, where I want to validate JWT on a subset of my GRPC api. I can currently implement that validation inside a CallHandlerProvider, but that gets ugly quick. The JWT validation is an async operation, but I need to respond synchronously with either a FailedFuture or SucceededFuture, so I'm forced to mark every request as Succeeded and move error handling into my proto service/message layer.

[whilesoftware]

Actually now I realize the async part of my JWT auth procedure can be factored out... so I suppose this isn't nearly as dire as I was making out.

Still up for contributing if this approach is sane :)

[glbrntt]

It's certainly on the roadmap. It's not clear to me that a ChannelHandler is the right abstraction here though. We need to explore this space some more before deciding on a solution.

[glbrntt]

This is available as of 1.0.0-alpha.21

[zsmatrix62]

how can I use the ClientInterceptor? any documentations?

[glbrntt]

I have an example/tutorial which needs tidying up, I'll try to post it in the next couple of days. In the meantime I'd suggesting looking at some of the tests as a starting point: https://github.com/grpc/grpc-swift/blob/main/Tests/GRPCTests/InterceptorsTests.swift#L298-#L325

[zsmatrix62]

I have an example/tutorial which needs tidying up, I'll try to post it in the next couple of days. In the meantime I'd suggesting looking at some of the tests as a starting point: https://github.com/grpc/grpc-swift/blob/main/Tests/GRPCTests/InterceptorsTests.swift#L298-#L325

thanks.

[glbrntt]

fyi, there is now a tutorial/example: https://github.com/grpc/grpc-swift/blob/main/docs/interceptors-tutorial.md