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/messages.go

@@ -0,0 +1,181 @@
+// 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
+
+import (
+	"encoding/json"
+
+	errors "golang.org/x/xerrors"
+)
+
+// ID is a Request identifier.
+type ID struct {
+	value interface{}
+}
+
+// Message is the interface to all jsonrpc2 message types.
+// They share no common functionality, but are a closed set of concrete types
+// that are allowed to implement this interface. The message types are *Request
+// and *Response.
+type Message interface {
+	// marshal builds the wire form from the API form.
+	// It is private, which makes the set of Message implementations closed.
+	marshal(to *wireCombined)
+}
+
+// Request is a Message sent to a peer to request behavior.
+// If it has an ID it is a call, otherwise it is a notification.
+type Request struct {
+	// ID of this request, used to tie the Response back to the request.
+	// This will be nil for notifications.
+	ID ID
+	// Method is a string containing the method name to invoke.
+	Method string
+	// Params is either a struct or an array with the parameters of the method.
+	Params json.RawMessage
+}
+
+// Response is a Message used as a reply to a call Request.
+// It will have the same ID as the call it is a response to.
+type Response struct {
+	// result is the content of the response.
+	Result json.RawMessage
+	// err is set only if the call failed.
+	Error error
+	// id of the request this is a response to.
+	ID ID
+}
+
+// StringID creates a new string request identifier.
+func StringID(s string) ID { return ID{value: s} }
+
+// Int64ID creates a new integer request identifier.
+func Int64ID(i int64) ID { return ID{value: i} }
+
+// IsValid returns true if the ID is a valid identifier.
+// The default value for ID will return false.
+func (id ID) IsValid() bool { return id.value != nil }
+
+// Raw returns the underlying value of the ID.
+func (id ID) Raw() interface{} { return id.value }
+
+// NewNotification constructs a new Notification message for the supplied
+// method and parameters.
+func NewNotification(method string, params interface{}) (*Request, error) {
+	p, merr := marshalToRaw(params)
+	return &Request{Method: method, Params: p}, merr
+}
+
+// NewCall constructs a new Call message for the supplied ID, method and
+// parameters.
+func NewCall(id ID, method string, params interface{}) (*Request, error) {
+	p, merr := marshalToRaw(params)
+	return &Request{ID: id, Method: method, Params: p}, merr
+}
+
+func (msg *Request) IsCall() bool { return msg.ID.IsValid() }
+
+func (msg *Request) marshal(to *wireCombined) {
+	to.ID = msg.ID.value
+	to.Method = msg.Method
+	to.Params = msg.Params
+}
+
+// NewResponse constructs a new Response message that is a reply to the
+// supplied. If err is set result may be ignored.
+func NewResponse(id ID, result interface{}, rerr error) (*Response, error) {
+	r, merr := marshalToRaw(result)
+	return &Response{ID: id, Result: r, Error: rerr}, merr
+}
+
+func (msg *Response) marshal(to *wireCombined) {
+	to.ID = msg.ID.value
+	to.Error = toWireError(msg.Error)
+	to.Result = msg.Result
+}
+
+func toWireError(err error) *wireError {
+	if err == nil {
+		// no error, the response is complete
+		return nil
+	}
+	if err, ok := err.(*wireError); ok {
+		// already a wire error, just use it
+		return err
+	}
+	result := &wireError{Message: err.Error()}
+	var wrapped *wireError
+	if errors.As(err, &wrapped) {
+		// if we wrapped a wire error, keep the code from the wrapped error
+		// but the message from the outer error
+		result.Code = wrapped.Code
+	}
+	return result
+}
+
+func EncodeMessage(msg Message) ([]byte, error) {
+	wire := wireCombined{VersionTag: wireVersion}
+	msg.marshal(&wire)
+	data, err := json.Marshal(&wire)
+	if err != nil {
+		return data, errors.Errorf("marshaling jsonrpc message: %w", err)
+	}
+	return data, nil
+}
+
+func DecodeMessage(data []byte) (Message, error) {
+	msg := wireCombined{}
+	if err := json.Unmarshal(data, &msg); err != nil {
+		return nil, errors.Errorf("unmarshaling jsonrpc message: %w", err)
+	}
+	if msg.VersionTag != wireVersion {
+		return nil, errors.Errorf("invalid message version tag %s expected %s", msg.VersionTag, wireVersion)
+	}
+	id := ID{}
+	switch v := msg.ID.(type) {
+	case nil:
+	case float64:
+		// coerce the id type to int64 if it is float64, the spec does not allow fractional parts
+		id = Int64ID(int64(v))
+	case int64:
+		id = Int64ID(v)
+	case string:
+		id = StringID(v)
+	default:
+		return nil, errors.Errorf("invalid message id type <%T>%v", v, v)
+	}
+	if msg.Method != "" {
+		// has a method, must be a call
+		return &Request{
+			Method: msg.Method,
+			ID:     id,
+			Params: msg.Params,
+		}, nil
+	}
+	// no method, should be a response
+	if !id.IsValid() {
+		return nil, ErrInvalidRequest
+	}
+	resp := &Response{
+		ID:     id,
+		Result: msg.Result,
+	}
+	// we have to check if msg.Error is nil to avoid a typed error
+	if msg.Error != nil {
+		resp.Error = msg.Error
+	}
+	return resp, nil
+}
+
+func marshalToRaw(obj interface{}) (json.RawMessage, error) {
+	if obj == nil {
+		return nil, nil
+	}
+	data, err := json.Marshal(obj)
+	if err != nil {
+		return nil, err
+	}
+	return json.RawMessage(data), nil
+}