AckingProtocolV1 only ever sends one ACK

[rdharrison2]

A while ago I wrote a Python lumberjack client for logstash-1.4.2 which uses ruby-lumberjack version 0.0.22. I recently upgraded to logstash-2.3.2 and this pulled in version 0.0.26 which seems to no longer send more than one ACK.

I've debugged it and have found that there is a bug in the AckingProtocolV1 logic which means it will only ever send one ACK. AckingProtocolV1 sets the sequence number for the next ACK as @next_ack in method ack? but this is only set on the first time when @next_ack is nil, and not updated when the server has sent an ACK. The only time it would be updated would be if the client sent another window_size frame (which mine doesn't).

[nhjm449]

I just started using the lumberjack logstash input plugin and was surprised to run into this issue.

But a simple patch helps:

--- lib/lumberjack/server.rb       2016-06-09 12:26:04.825827010 -0500
+++ lib/lumberjack/server.rb       2016-06-09 12:31:21.257811427 -0500
@@ -392,7 +392,12 @@
       # The first encoded event will contain the sequence number 
       # this is needed to know when we should ack.
       @next_ack = compute_next_ack(sequence) if @next_ack.nil?
-      sequence == @next_ack
+      if sequence == @next_ack
+        @next_ack = compute_next_ack(sequence + 1)
+        true
+      else
+        false
+      end
     end

     def ack_frame(sequence)