Butler stream servers can generate client address.

logdog/client/cmd/logdog_butler/main_windows.go

Index: logdog/client/cmd/logdog_butler/main_windows.go
diff --git a/logdog/client/cmd/logdog_butler/main_windows.go b/logdog/client/cmd/logdog_butler/main_windows.go
index a9de4f18b01c376d984973e6caa66e2cc7b81425..9d38a244aaace0e6f1dfe38fe08a50b61f65ce4b 100644
--- a/logdog/client/cmd/logdog_butler/main_windows.go
+++ b/logdog/client/cmd/logdog_butler/main_windows.go
@@ -6,7 +6,6 @@ package main
 
 import (
 	"errors"
-	"fmt"
 	"os"
 
 	"github.com/luci/luci-go/logdog/client/butler/streamserver"
@@ -47,10 +46,10 @@ func (u streamServerURI) Validate() error {
 }
 
 // Create a Windows stream server.
-func createStreamServer(ctx context.Context, uri streamServerURI) streamserver.StreamServer {
+func createStreamServer(ctx context.Context, uri streamServerURI) (streamserver.StreamServer, error) {
 	name, err := uri.Parse()
 	if err != nil {
 		panic("Failed to parse stream server URI.")
 	}
-	return streamserver.NewNamedPipeServer(ctx, fmt.Sprintf(`\\.\pipe\%s`, name))
+	return streamserver.NewNamedPipeServer(ctx, name)
 }