Add NIP-01 compliant client code

spec/support/echo_server.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'puma'
+require 'puma/binder'
+require 'puma/events'
+
+class EchoServer
+  def call(env)
+    @socket = Faye::WebSocket.new(env, ['echo'])
+
+    @socket.onmessage = lambda do |event|
+      @socket.send(event.data)
+    end
+
+    @socket.rack_response
+  end
+
+  def send(message)
+    @socket.send(message)
+  end
+
+  def close(code, reason)
+    @socket.close(code, reason)
+  end
+
+  def log(*args); end
+
+  def listen(port)
+    events = Puma::Events.new(StringIO.new, StringIO.new)
+    binder = Puma::Binder.new(events)
+    binder.parse(["tcp://0.0.0.0:#{port}"], self)
+    @server = Puma::Server.new(self, events)
+    @server.binder = binder
+    @server.run
+  end
+
+  def stop
+    case @server
+    when Puma::Server then @server.stop(true)
+    else @server.stop
+    end
+  end
+end