reduce calls to Debugf when not debugging to reduce slice allocs

ref #129

frames/log.go

@@ -0,0 +1,19 @@
+package frames
+
+import "github.com/lucas-clemente/quic-go/utils"
+
+// LogFrame logs a frame, either sent or received
+func LogFrame(frame Frame, sent bool) {
+	if !utils.Debug() {
+		return
+	}
+	dir := "<-"
+	if sent {
+		dir = "->"
+	}
+	if sf, ok := frame.(*StreamFrame); ok {
+		utils.Debugf("\t%s &frames.StreamFrame{StreamID: %d, FinBit: %t, Offset: 0x%x, Data length: 0x%x, Offset + Data length: 0x%x}", dir, sf.StreamID, sf.FinBit, sf.Offset, sf.DataLen(), sf.Offset+sf.DataLen())
+	} else {
+		utils.Debugf("\t%s %#v", dir, frame)
+	}
+}