compressable.rb lost some data on decompression

[komeda-shinji]

When sender fluend enable compress gzip, reciever fluend lost some data.

I put logging code to lib/fluent/plugin/compressable.rb, debug messages show unused is nil, but input stream is not EOF.
unused.nil? does not show end of stream.

--- compressable.rb-	2018-10-11 12:11:31.000000000 +0900
+++ compressable.rb	2019-08-08 13:26:25.589042228 +0900
@@ -64,6 +64,7 @@
           unused = gz.unused
           gz.finish
 
+          $log.debug "string_decompress", unused: (unused.nil? ? "nil" : "defined"), eof: (io.eof ? "EOF" : "not")
           break if unused.nil?
           adjust = unused.length
           io.pos -= adjust

2019-08-08 13:19:16 +0900 [debug]: #0 string_decompress unused="defined" eof="not"
2019-08-08 13:19:16 +0900 [debug]: #0 string_decompress unused="defined" eof="not"
2019-08-08 13:19:16 +0900 [debug]: #0 string_decompress unused="nil" eof="not"

I change check eof, then is works fine.

--- a/lib/fluent/plugin/compressable.rb
+++ b/lib/fluent/plugin/compressable.rb
@@ -64,9 +64,11 @@ module Fluent
           unused = gz.unused
           gz.finish
 
-          break if unused.nil?
-          adjust = unused.length
-          io.pos -= adjust
+          unless unused.nil?
+            adjust = unused.length
+            input.pos -= adjust
+          end
+          break if io.eof?
         end
 
         out