internal/lsp/cmd: add a test for client logging

A new test is added to verify that contextual logs are reflected back to
the LSP client. In the future when we are considering servers with
multiple clients, this test will be used to verify that client log
exporting is scoped to the specific client session.

Updates golang/go#34111.

Change-Id: I29044e5355e25b81a759d064929520345230ea82
Reviewed-on: https://go-review.googlesource.com/c/tools/+/215739
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cmd/serve_test.go

@@ -0,0 +1,86 @@
+package cmd
+
+import (
+	"context"
+	"io"
+	"regexp"
+	"testing"
+	"time"
+
+	"golang.org/x/tools/internal/jsonrpc2"
+	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/telemetry/log"
+)
+
+type fakeServer struct {
+	protocol.Server
+	client protocol.Client
+}
+
+func (s *fakeServer) DidOpen(ctx context.Context, params *protocol.DidOpenTextDocumentParams) error {
+	// Our instrumentation should cause this message to be logged back to the LSP
+	// client.
+	log.Print(ctx, "ping")
+	return nil
+}
+
+type fakeClient struct {
+	protocol.Client
+
+	logs chan string
+}
+
+func (c *fakeClient) LogMessage(ctx context.Context, params *protocol.LogMessageParams) error {
+	c.logs <- params.Message
+	return nil
+}
+
+func TestClientLogging(t *testing.T) {
+	server := &fakeServer{}
+	client := &fakeClient{logs: make(chan string)}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// Bind our fake client and server.
+	// sReader and sWriter read from and write to the server. cReader and cWriter
+	// read from and write to the client.
+	sReader, sWriter := io.Pipe()
+	cReader, cWriter := io.Pipe()
+	close := func() {
+		failOnErr := func(err error) {
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+		failOnErr(sReader.Close())
+		failOnErr(cReader.Close())
+		failOnErr(sWriter.Close())
+		failOnErr(cWriter.Close())
+	}
+	defer close()
+	serverStream := jsonrpc2.NewStream(sReader, cWriter)
+	// The returned client dispatches to the client, but it is already stored
+	// in the context by NewServer, so we can ignore it.
+	serverCtx, serverConn, _ := protocol.NewServer(ctx, serverStream, server)
+	serverConn.AddHandler(&handler{})
+	clientStream := jsonrpc2.NewStream(cReader, sWriter)
+	clientCtx, clientConn, serverDispatch := protocol.NewClient(ctx, clientStream, client)
+
+	go clientConn.Run(clientCtx)
+	go serverConn.Run(serverCtx)
+	serverDispatch.DidOpen(ctx, &protocol.DidOpenTextDocumentParams{})
+
+	select {
+	case got := <-client.logs:
+		want := "ping"
+		matched, err := regexp.MatchString(want, got)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !matched {
+			t.Errorf("got log %q, want a log containing %q", got, want)
+		}
+	case <-time.After(1 * time.Second):
+		t.Error("timeout waiting for client log")
+	}
+}