The two tiers

godot-grpc exposes the same transport through two layers. Both run over the identical channel/runtime/bridge; they differ only in how messages are represented on the GDScript side.

Tier 1 — raw bytes

The lowest level. You hand GrpcChannel an already-encoded request and receive encoded response bytes; you decode them yourself (e.g. with a generated prost type on the Rust side, or a GDScript protobuf library).

var channel := GrpcChannel.tcp("http://127.0.0.1:50051")
var call := channel.unary_call("/greeter.Greeter/SayHello", request_bytes)
call.completed.connect(func(bytes: PackedByteArray): ...)  # decode yourself

The method path is /<package>.<Service>/<Method>. Streaming uses server_stream_call, client_stream_call, and bidi_call.

Tier 2 — runtime descriptors

Load a FileDescriptorSet into a GrpcDescriptorPool and call services by name with Dictionary requests; responses come back as GrpcMessage objects with get_field / set_field / to_dict.

var pool := GrpcDescriptorPool.new()
pool.load_file("res://greeter.descriptor.bin")
var channel := GrpcChannel.tcp("http://127.0.0.1:50051")
var stub := pool.service("greeter.Greeter").client(channel)
var call := stub.unary("SayHello", { "name": "world" })
call.completed.connect(func(reply): print(reply.get_field("message")))

GrpcServiceStub methods: unary, server_stream, client_stream, bidi (named unary — not call — because Object.call is a Godot built-in).

The result of either is a GrpcCall

Every call returns a GrpcCall with these signals:

• completed(response) — success (unary) or end-of-stream.
• stream_item(message) — one server-/bidi-stream message.
• failed(status: GrpcStatus) — a gRPC or transport error.
• cancelled().

In tier 1 the payloads are PackedByteArray; in tier 2 they are GrpcMessage.