Abstract out making a cancel message

connection.go

@@ -355,12 +355,7 @@ func (cn *connection) fillWriteBuffer(msg func(pp.Message) bool) {
 		for r := range cn.requests {
 			cn.deleteRequest(r)
 			// log.Printf("%p: cancelling request: %v", cn, r)
-			if !msg(pp.Message{
-				Type:   pp.Cancel,
-				Index:  r.Index,
-				Begin:  r.Begin,
-				Length: r.Length,
-			}) {
+			if !msg(makeCancelMessage(r)) {
 				return
 			}
 		}

peer_protocol/protocol.go

@@ -261,3 +261,12 @@ func marshalBitfield(bf []bool) (b []byte) {
 	}
 	return
 }
+
+func MakeCancelMessage(piece, offset, length Integer) Message {
+	return Message{
+		Type:   Cancel,
+		Index:  piece,
+		Begin:  offset,
+		Length: length,
+	}
+}

protocol.go

@@ -0,0 +1,9 @@
+package torrent
+
+import (
+	pp "github.com/anacrolix/torrent/peer_protocol"
+)
+
+func makeCancelMessage(r request) pp.Message {
+	return pp.MakeCancelMessage(r.Index, r.Begin, r.Length)
+}