Refactor compression support, now at message level.

protocol/header.go

@@ -7,9 +7,10 @@ package protocol
 import "github.com/calmh/syncthing/xdr"
 
 type header struct {
-	version int
-	msgID   int
-	msgType int
+	version     int
+	msgID       int
+	msgType     int
+	compression bool
 }
 
 func (h header) encodeXDR(xw *xdr.Writer) (int, error) {
@@ -24,15 +25,21 @@ func (h *header) decodeXDR(xr *xdr.Reader) error {
 }
 
 func encodeHeader(h header) uint32 {
+	var isComp uint32
+	if h.compression {
+		isComp = 1 << 0 // the zeroth bit is the compression bit
+	}
 	return uint32(h.version&0xf)<<28 +
 		uint32(h.msgID&0xfff)<<16 +
-		uint32(h.msgType&0xff)<<8
+		uint32(h.msgType&0xff)<<8 +
+		isComp
 }
 
 func decodeHeader(u uint32) header {
 	return header{
-		version: int(u>>28) & 0xf,
-		msgID:   int(u>>16) & 0xfff,
-		msgType: int(u>>8) & 0xff,
+		version:     int(u>>28) & 0xf,
+		msgID:       int(u>>16) & 0xfff,
+		msgType:     int(u>>8) & 0xff,
+		compression: u&1 == 1,
 	}
 }