Heartbeat support

Server should send heartbeat frames to client depending on the
negotiated heartbeat interval.

Probably fixes #140

src/amqproxy/client.cr

@@ -13,6 +13,7 @@ module AMQProxy
     @frame_max : UInt32
     @channel_max : UInt16
     @heartbeat : UInt16
+    @last_heartbeat = Time.monotonic
 
     def initialize(@socket : TCPSocket)
       set_socket_options(@socket)
@@ -27,9 +28,11 @@ module AMQProxy
     def read_loop(channel_pool, socket = @socket) # ameba:disable Metrics/CyclomaticComplexity
       Log.context.set(remote_address: socket.remote_address.to_s)
       Log.debug { "Connected" }
+      socket.read_timeout = (@heartbeat / 2).ceil.seconds if @heartbeat > 0
       loop do
         case frame = AMQ::Protocol::Frame.from_io(socket, IO::ByteFormat::NetworkEndian)
-        when AMQ::Protocol::Frame::Heartbeat           then write frame
+        when AMQ::Protocol::Frame::Heartbeat
+          @last_heartbeat = Time.monotonic
         when AMQ::Protocol::Frame::Connection::CloseOk then return
         when AMQ::Protocol::Frame::Connection::Close
           close_all_upstream_channels
@@ -61,6 +64,15 @@ module AMQProxy
             close_connection(504_u16, "CHANNEL_ERROR - Channel #{frame.channel} not open", frame)
           end
         end
+      rescue IO::TimeoutError
+        time_since_last_heartbeat = (Time.monotonic - @last_heartbeat).total_seconds.to_i # ignore subsecond latency
+        if time_since_last_heartbeat <= 1 + @heartbeat                                    # add 1s grace because of rounding
+          Log.debug { "Sending heartbeat (last heartbeat #{time_since_last_heartbeat}s ago)" }
+          write AMQ::Protocol::Frame::Heartbeat.new
+        else
+          Log.warn { "No heartbeat response in #{time_since_last_heartbeat}s (max #{1 + @heartbeat}s), closing connection" }
+          return
+        end
       end
     rescue ex : IO::EOFError
       Log.debug { "Disconnected" }