internal/jsonrpc2_v2: update for go1.16+

Change-Id: If70bb4b7ab236ae921ff23d123cb38d476cfa665
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676516
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/jsonrpc2/net.go

@@ -100,14 +100,14 @@ func (l *netPiper) Accept(context.Context) (io.ReadWriteCloser, error) {
 	// preferring the latter if already closed at the start of Accept.
 	select {
 	case <-l.done:
-		return nil, errClosed
+		return nil, net.ErrClosed
 	default:
 	}
 	select {
 	case rwc := <-l.dialed:
 		return rwc, nil
 	case <-l.done:
-		return nil, errClosed
+		return nil, net.ErrClosed
 	}
 }
 
@@ -133,6 +133,6 @@ func (l *netPiper) Dial(ctx context.Context) (io.ReadWriteCloser, error) {
 	case <-l.done:
 		client.Close()
 		server.Close()
-		return nil, errClosed
+		return nil, net.ErrClosed
 	}
 }

internal/jsonrpc2/serve_go116.go

@@ -1,13 +0,0 @@
-// Copyright 2022 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.
-
-//go:build go1.16
-
-package jsonrpc2
-
-import (
-	"net"
-)
-
-var errClosed = net.ErrClosed

internal/jsonrpc2/serve_pre116.go

@@ -1,15 +0,0 @@
-// Copyright 2020 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.
-
-//go:build !go1.16
-
-package jsonrpc2
-
-import (
-	"errors"
-)
-
-// errClosed is an error with the same string as net.ErrClosed,
-// which was added in Go 1.16.
-var errClosed = errors.New("use of closed network connection")