Cookbook: streaming RPCs

lean-grpc exposes both low-level duplex (openStream) and batch helpers for the three streaming shapes.

Client helpers

Helper	Shape
Grpc.Channel.serverStream	one request → many responses
Grpc.Channel.clientStream	many requests → one response
Grpc.Channel.bidiStream	many → many (send all, then recv all)
Grpc.Channel.openStream	interactive StreamWriter / StreamReader

-- Server streaming
let (msgs, st) ← Grpc.Channel.serverStream ch "svc" "List" reqBytes
-- Client streaming
let res ← Grpc.Channel.clientStream ch "svc" "Record" reqArray
-- Bidi (batch)
let (echo, st) ← Grpc.Channel.bidiStream ch "svc" "Chat" reqArray

Interactive duplex (send/recv interleaved):

let stream ← Grpc.Channel.openStream ch "svc" "Chat"
Grpc.Stream.StreamWriter.send stream.writer msg1
match ← Grpc.Stream.StreamReader.recv? stream.reader with
| some raw => pure ()
| none => pure ()
Grpc.Stream.StreamWriter.halfClose stream.writer
let rest ← Grpc.Stream.StreamReader.recvAll stream.reader

Server helpers

Raw ByteArray registers still work. Prefer typed adapters when you have codecs:

s := Grpc.Server.registerServerStreamTyped s "svc" "List"
  Req.decode Resp.encode fun req => do
    pure (#[resp1, resp2], .ok)

s := Grpc.Server.registerClientStreamTyped s "svc" "Record"
  Req.decode Resp.encode fun reqs => do
    pure (aggregate reqs, .ok)

s := Grpc.Server.registerBidiTyped s "svc" "Chat"
  Req.decode Resp.encode fun reqs => do
    pure (reqs, .ok)  -- echo

Worked example

Examples/RouteGuide/ — unary + all three streaming shapes on both sides.

Limitations

• Server handlers are still batch (arrays), not callback-driven writers.
• True ping-pong duplex on the server is incremental only for bidi DATA chunks (see Grpc.Server.handlerFor).
• Descriptor codegen emits typed client streaming stubs; streaming server register helpers are the *Typed APIs above.

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Source: docs/cookbook-streaming.md in RileyBetts/lean-grpc. Hosted docs may lag the repository slightly.