Butler stream servers can generate client address.

logdog/client/butler/streamserver/streamserver.go

Index: logdog/client/butler/streamserver/streamserver.go
diff --git a/logdog/client/butler/streamserver/streamserver.go b/logdog/client/butler/streamserver/streamserver.go
index e63f5c35bfc4835de97a59d2093f641a52696d8f..c940cb533adc4fe79215a4637c8c3cdedc2f7bc9 100644
--- a/logdog/client/butler/streamserver/streamserver.go
+++ b/logdog/client/butler/streamserver/streamserver.go
@@ -15,9 +15,20 @@ import (
 type StreamServer interface {
 	// Performs initial connection and setup, entering a listening state.
 	Listen() error
+
+	// Address returns a string that can be used by the "streamclient" package to
+	// return a client for this StreamServer.
+	//
+	// Full package is:
+	// github.com/luci/luci-go/logdog/butlerlib/streamclient
+	//
+	// Address may only be called while the StreamServer is actively listening.
+	Address() string
+
 	// Blocks, returning a new Stream when one is available. If the stream server
 	// has closed, this will return nil.
 	Next() (io.ReadCloser, *streamproto.Properties)
+
 	// Closes the stream server, cleaning up resources.
 	Close()
 }