Merge pull request #129 from loadhigh/master

Speed up Deflater sysread speed when number_of_bytes is small and @output_buffer is large

lib/zip/inflater.rb

@@ -4,26 +4,42 @@ module Zip
       super
       @zlib_inflater           = ::Zlib::Inflate.new(-Zlib::MAX_WBITS)
       @output_buffer           = ''
+      @output_buffer_pos       = 0
       @has_returned_empty_string = false
     end
 
     def sysread(number_of_bytes = nil, buf = '')
+      buf ||= ''
+      buf.clear
       readEverything = number_of_bytes.nil?
-      while readEverything || @output_buffer.bytesize < number_of_bytes
-        break if internal_input_finished?
-        @output_buffer << internal_produce_input(buf)
+      if readEverything
+        buf << @output_buffer[@output_buffer_pos...@output_buffer.bytesize]
+
+        move_output_buffer_pos(buf.bytesize)
+      else
+        buf << @output_buffer[@output_buffer_pos, number_of_bytes]
+
+        move_output_buffer_pos(buf.bytesize)
+
+        if buf.bytesize == number_of_bytes
+          return buf
+        end
       end
-      return value_when_finished if @output_buffer.bytesize == 0 && input_finished?
-      end_index = number_of_bytes.nil? ? @output_buffer.bytesize : number_of_bytes
-      @output_buffer.slice!(0...end_index)
+      while readEverything || buf.bytesize + @output_buffer.bytesize < number_of_bytes
+        break if internal_input_finished?
+        @output_buffer << internal_produce_input
+      end
+      return value_when_finished(number_of_bytes, buf) if @output_buffer.bytesize == 0 && input_finished?
+      end_index = (number_of_bytes.nil? ? @output_buffer.bytesize : number_of_bytes) - buf.bytesize
+      data = @output_buffer[0...end_index]
+
+      move_output_buffer_pos(data.bytesize)
+
+      buf << data
     end
 
     def produce_input
-      if (@output_buffer.empty?)
-        internal_produce_input
-      else
-        @output_buffer.slice!(0...(@output_buffer.length))
-      end
+      sysread()
     end
 
     # to be used with produce_input, not read (as read may still have more data cached)
@@ -37,7 +53,16 @@ module Zip
 
     private
 
-    def internal_produce_input(buf = '')
+    def move_output_buffer_pos(inc)
+      @output_buffer_pos += inc
+      if @output_buffer_pos == @output_buffer.bytesize
+        @output_buffer.clear
+        @output_buffer_pos = 0
+      end
+    end
+
+    def internal_produce_input
+      buf = ''
       retried = 0
       begin
         @zlib_inflater.inflate(@input_stream.read(Decompressor::CHUNK_SIZE, buf))
@@ -52,10 +77,14 @@ module Zip
       @zlib_inflater.finished?
     end
 
-    def value_when_finished # mimic behaviour of ruby File object.
-      return if @has_returned_empty_string
-      @has_returned_empty_string = true
-      ''
+    def value_when_finished(number_of_bytes, buf) # mimic behaviour of ruby File object.
+      if number_of_bytes.nil?
+        buf
+      elsif buf.bytesize == 0
+        nil
+      else
+        buf
+      end
     end
   end
 end