pick a random port for tunnel if none are available

Change-Id: I65b49019ad67091c554adbaaf1401b5d92e1cb00

lib/cli/commands/services.rb

@@ -114,9 +114,6 @@ def tunnel(service=nil, client_name=nil)
 
       err "Unknown service '#{service}'" unless info
 
-      # TODO: rather than default to a particular port, we should get
-      # the defaults based on the service name.. i.e. known services should
-      # have known local default ports for this side of the tunnel.
       port = pick_tunnel_port(@options[:port] || 10000)
 
       raise VMC::Client::AuthError unless client.logged_in?

lib/cli/tunnel_helper.rb

@@ -210,12 +210,21 @@ def pick_tunnel_port(port)
         begin
           TCPSocket.open('localhost', port)
           port += 1
-        rescue => e
+        rescue
           return port
         end
       end
 
-      err "Could not pick a port between #{original} and #{original + PORT_RANGE - 1}"
+      grab_ephemeral_port
+    end
+
+    def grab_ephemeral_port
+      socket = TCPServer.new('0.0.0.0', 0)
+      socket.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEADDR, true)
+      Socket.do_not_reverse_lookup = true
+      port = socket.addr[1]
+      socket.close
+      return port
     end
 
     def wait_for_tunnel_start(port)