Fix high memory usage due to Deflater buffering

When support for ZipCrypto was added, an internal StringIO buffer was
added to Deflater, in order to fix a decryption bug. While this worked,
it caused unlimited memory growth when compressing large files. The
proper fix is to writer the encryption header in init_next_entry instead
of finalize_current_entry, so the headers are written before any
encrypted data. Because of this fix we can remove the buffering in
Deflater, which keeps memory usage low and allows to stream compressed
data while it is written.

This should fix issue #233.

lib/zip/deflater.rb

@@ -7,18 +7,21 @@ def initialize(output_stream, level = Zip.default_compression, encrypter = NullE
       @size          = 0
       @crc           = ::Zlib.crc32
       @encrypter     = encrypter
-      @buffer_stream = ::StringIO.new('')
     end
 
     def <<(data)
       val   = data.to_s
       @crc  = Zlib.crc32(val, @crc)
       @size += val.bytesize
-      @buffer_stream << @zlib_deflater.deflate(data)
+      buffer = @zlib_deflater.deflate(data)
+      if buffer.empty?
+        @output_stream
+      else
+        @output_stream << @encrypter.encrypt(buffer)
+      end
     end
 
     def finish
-      @output_stream << @encrypter.encrypt(@buffer_stream.string)
       @output_stream << @encrypter.encrypt(@zlib_deflater.finish) until @zlib_deflater.finished?
     end
 

lib/zip/output_stream.rb

@@ -123,7 +123,6 @@ def copy_raw_entry(entry)
 
     def finalize_current_entry
       return unless @current_entry
-      @output_stream << @encrypter.header(@current_entry.mtime)
       finish
       @current_entry.compressed_size = @output_stream.tell - @current_entry.local_header_offset - @current_entry.calculate_local_header_size
       @current_entry.size = @compressor.size
@@ -139,6 +138,7 @@ def init_next_entry(entry, level = Zip.default_compression)
       @entry_set << entry
       entry.write_local_entry(@output_stream)
       @encrypter.reset!
+      @output_stream << @encrypter.header(entry.mtime)
       @compressor = get_compressor(entry, level)
     end