Merge pull request #44 from Shopify/compression_mask_magic

Get rid of a magic value of the compression codec mask

message.go

@@ -10,6 +10,9 @@ import (
 // CompressionCodec represents the various compression codecs recognized by Kafka in messages.
 type CompressionCodec int8
 
+// only the last three bits are really used
+const compressionCodecMask int8 = 0x07
+
 const (
 	CompressionNone   CompressionCodec = 0
 	CompressionGZIP   CompressionCodec = 1
@@ -33,7 +36,7 @@ func (m *Message) encode(pe packetEncoder) error {
 
 	pe.putInt8(messageFormat)
 
-	attributes := int8(m.Codec) & 0x07
+	attributes := int8(m.Codec) & compressionCodecMask
 	pe.putInt8(attributes)
 
 	err := pe.putBytes(m.Key)
@@ -95,7 +98,7 @@ func (m *Message) decode(pd packetDecoder) (err error) {
 	if err != nil {
 		return err
 	}
-	m.Codec = CompressionCodec(attribute & 0x07)
+	m.Codec = CompressionCodec(attribute & compressionCodecMask)
 
 	m.Key, err = pd.getBytes()
 	if err != nil {