add a function to distinguish between short and long header packets

internal/wire/header.go

@@ -10,6 +10,11 @@ import (
 	"github.com/lucas-clemente/quic-go/internal/utils"
 )
 
+// IsLongHeader says if a packet is a long header packet.
+func IsLongHeader(firstByte byte) bool {
+	return firstByte&0x80 > 0
+}
+
 // ParseConnectionID parses the destination connection ID of a packet.
 // It uses the data slice for the connection ID.
 // That means that the connection ID must not be used after the packet buffer is released.

internal/wire/header_test.go

@@ -18,6 +18,11 @@ var _ = Describe("Header Parsing", func() {
 		return data
 	}
 
+	It("distinguishes between long and short header packets", func() {
+		Expect(IsLongHeader(0b10101011)).To(BeTrue())
+		Expect(IsLongHeader(0b00101011)).To(BeFalse())
+	})
+
 	Context("Parsing the Connection ID", func() {
 		It("parses the connection ID of a long header packet", func() {
 			buf := &bytes.Buffer{}