implement basic public header writing

public_header.go

@@ -72,3 +72,11 @@ func ParsePublicHeader(b io.ByteReader) (*PublicHeader, error) {
 
 	return header, nil
 }
+
+// WritePublicHeader writes a public header
+func WritePublicHeader(b *bytes.Buffer, h *PublicHeader) {
+	publicFlagByte := uint8(0x0C | 0x20)
+	b.WriteByte(publicFlagByte)
+	utils.WriteUint64(b, h.ConnectionID)         // TODO: Send shorter connection id if possible
+	utils.WriteUint32(b, uint32(h.PacketNumber)) // TODO: Send shorter packet number if possible
+}

public_header_test.go

@@ -72,4 +72,15 @@ var _ = Describe("Public Header", func() {
 			Expect(b.Len()).To(BeZero())
 		})
 	})
+
+	Context("when writing", func() {
+		It("writes a sample header", func() {
+			b := &bytes.Buffer{}
+			WritePublicHeader(b, &PublicHeader{
+				ConnectionID: 1,
+				PacketNumber: 2,
+			})
+			Expect(b.Bytes()).To(Equal([]byte{0x2c, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0}))
+		})
+	})
 })