Don't panic on unknown token_id in gRPC callbacks.

[erikness-doordash]

Sometimes Dispatcher.on_grpc_receive_initial_metadata() will get an invalid stream ID, and then panic. Dispatcher.on_grpc_receive_trailing_metadata() as well.

This is a quick fix that will turn a panic!() call into a trace!() call. The broader issue/bug is out of scope here, though as far as I know it's benign other than this panic.

NOTE: there may be a more concise way to write this Rust code. (thanks Piotr)
NOTE: adding this change to on_grpc_receive() as well, just to be safe, even though I haven't seen this panic get triggered myself.

See:

1. Issue with more details: Panic when there are no remote hosts #206
2. Issue tracking why these two methods get an invalid token number at all: gRPC callbacks are reentrant, defer them proxy-wasm-cpp-host#373

[erikness-doordash]

Just tested this, no more crash after scaling a remote service to 0

[PiotrSikora]

I think this could be written as:

let context_id = match self.grpc_streams.borrow_mut().get(&token_id) {

[erikness-doordash]

For some reason I thought the rust compiler would stop me. Checked again though, it works fine, thanks for the tip

[PiotrSikora]

Could you fix DCO?

[erikness-doordash]

Code search to support patching on_grpc_receive() as well

I went looking through the host code; I couldn't find where exactly Envoy calls these methods in the unhappy path (can't init stream), it may be pretty low level.

But looking at this call stack, I suspect on_grpc_receive() needs this too:

1. (proxy-wasm-cpp-host) ContextBase::onGrpcReceiveInitialMetadata
2. (envoy) Context::onGrpcReceiveInitialMetadataWrapper()
3. (envoy) GrpcStreamClientHandler::onReceiveInitialMetadata()
   1. AsyncStreamImpl::onHeaders()
      1. AsyncStreamImpl::encodeHeaders()
      2. ???
   2. GoogleAsyncStreamImpl::handleOpCompletion()
      • This has a branch for 2 methods on the "callbacks_" object: onReceiveInitialMetadata() and onReceiveMessageRaw()

(similar for trailing metadata)

Though I have not seen on_grpc_receive() calls triggered in our own code in this circumstance (see: #206).

[PiotrSikora]

LGTM, sans the nit.

[erikness-doordash]

LGTM, sans the nit.

@PiotrSikora can you merge it?

[PiotrSikora]

Thanks!