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// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package lsprpc
import (
jsonrpc2_v2 ""
// Metadata holds arbitrary data transferred between jsonrpc2 peers.
type Metadata map[string]interface{}
// PeerInfo holds information about a peering between jsonrpc2 servers.
type PeerInfo struct {
// RemoteID is the identity of the current server on its peer.
RemoteID int64
// LocalID is the identity of the peer on the server.
LocalID int64
// IsClient reports whether the peer is a client. If false, the peer is a
// server.
IsClient bool
// Metadata holds arbitrary information provided by the peer.
Metadata Metadata
// Handshaker handles both server and client handshaking over jsonrpc2. To
// instrument server-side handshaking, use Handshaker.Middleware. To instrument
// client-side handshaking, call Handshaker.ClientHandshake for any new
// client-side connections.
type Handshaker struct {
// Metadata will be shared with peers via handshaking.
Metadata Metadata
mu sync.Mutex
prevID int64
peers map[int64]PeerInfo
// Peers returns the peer info this handshaker knows about by way of either the
// server-side handshake middleware, or client-side handshakes.
func (h *Handshaker) Peers() []PeerInfo {
var c []PeerInfo
for _, v := range h.peers {
c = append(c, v)
return c
// Middleware is a jsonrpc2 middleware function to augment connection binding
// to handle the handshake method, and record disconnections.
func (h *Handshaker) Middleware(inner jsonrpc2_v2.Binder) jsonrpc2_v2.Binder {
return BinderFunc(func(ctx context.Context, conn *jsonrpc2_v2.Connection) jsonrpc2_v2.ConnectionOptions {
opts := inner.Bind(ctx, conn)
localID := h.nextID()
info := &PeerInfo{
RemoteID: localID,
Metadata: h.Metadata,
// Wrap the delegated handler to accept the handshake.
delegate := opts.Handler
opts.Handler = jsonrpc2_v2.HandlerFunc(func(ctx context.Context, req *jsonrpc2_v2.Request) (interface{}, error) {
if req.Method == handshakeMethod {
var peerInfo PeerInfo
if err := json.Unmarshal(req.Params, &peerInfo); err != nil {
return nil, fmt.Errorf("%w: unmarshaling client info: %v", jsonrpc2_v2.ErrInvalidParams, err)
peerInfo.LocalID = localID
peerInfo.IsClient = true
return info, nil
return delegate.Handle(ctx, req)
// Record the dropped client.
go h.cleanupAtDisconnect(conn, localID)
return opts
// ClientHandshake performs a client-side handshake with the server at the
// other end of conn, recording the server's peer info and watching for conn's
// disconnection.
func (h *Handshaker) ClientHandshake(ctx context.Context, conn *jsonrpc2_v2.Connection) {
localID := h.nextID()
info := &PeerInfo{
RemoteID: localID,
Metadata: h.Metadata,
call := conn.Call(ctx, handshakeMethod, info)
var serverInfo PeerInfo
if err := call.Await(ctx, &serverInfo); err != nil {
event.Error(ctx, "performing handshake", err)
serverInfo.LocalID = localID
go h.cleanupAtDisconnect(conn, localID)
func (h *Handshaker) nextID() int64 {
return h.prevID
func (h *Handshaker) cleanupAtDisconnect(conn *jsonrpc2_v2.Connection, peerID int64) {
delete(h.peers, peerID)
func (h *Handshaker) recordPeer(info PeerInfo) {
if h.peers == nil {
h.peers = make(map[int64]PeerInfo)
h.peers[info.LocalID] = info