internal/jsonrpc2_v2: an updated jsonrpc2 library

Change-Id: I609173baa6842d33068a7e9596d54f03d89c5401
Reviewed-on: https://go-review.googlesource.com/c/tools/+/292169
Run-TryBot: Ian Cottrell <iancottrell@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Ian Cottrell <iancottrell@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

internal/jsonrpc2/jsonrpc2.go

@@ -0,0 +1,84 @@
+// Copyright 2018 The Go MCP SDK Authors. All rights reserved.
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+// Package jsonrpc2 is a minimal implementation of the JSON RPC 2 spec.
+// https://www.jsonrpc.org/specification
+// It is intended to be compatible with other implementations at the wire level.
+package jsonrpc2
+
+import (
+	"context"
+	"errors"
+)
+
+var (
+	// ErrIdleTimeout is returned when serving timed out waiting for new connections.
+	ErrIdleTimeout = errors.New("timed out waiting for new connections")
+	// ErrNotHandled is returned from a handler to indicate it did not handle the
+	// message.
+	ErrNotHandled = errors.New("JSON RPC not handled")
+	// ErrAsyncResponse is returned from a handler to indicate it will generate a
+	// response asynchronously.
+	ErrAsyncResponse = errors.New("JSON RPC asynchronous response")
+)
+
+// Preempter handles messages on a connection before they are queued to the main
+// handler.
+// Primarily this is used for cancel handlers or notifications for which out of
+// order processing is not an issue.
+type Preempter interface {
+	// Preempt is invoked for each incoming request before it is queued.
+	// If the request is a call, it must return a value or an error for the reply.
+	// Preempt should not block or start any new messages on the connection.
+	Preempt(ctx context.Context, req *Request) (interface{}, error)
+}
+
+// Handler handles messages on a connection.
+type Handler interface {
+	// Handle is invoked for each incoming request.
+	// If the request is a call, it must return a value or an error for the reply.
+	Handle(ctx context.Context, req *Request) (interface{}, error)
+}
+
+type defaultHandler struct{}
+
+func (defaultHandler) Preempt(context.Context, *Request) (interface{}, error) {
+	return nil, ErrNotHandled
+}
+
+func (defaultHandler) Handle(context.Context, *Request) (interface{}, error) {
+	return nil, ErrNotHandled
+}
+
+// async is a small helper for things with an asynchronous result that you can
+// wait for.
+type async struct {
+	ready  chan struct{}
+	errBox chan error
+}
+
+func (a *async) init() {
+	a.ready = make(chan struct{})
+	a.errBox = make(chan error, 1)
+	a.errBox <- nil
+}
+
+func (a *async) done() {
+	close(a.ready)
+}
+
+func (a *async) wait() error {
+	<-a.ready
+	err := <-a.errBox
+	a.errBox <- err
+	return err
+}
+
+func (a *async) setError(err error) {
+	storedErr := <-a.errBox
+	if storedErr == nil {
+		storedErr = err
+	}
+	a.errBox <- storedErr
+}