retransmit Initial packets as Initial packets

internal/ackhandler/packet.go

@@ -11,6 +11,7 @@ import (
 // +gen linkedlist
 type Packet struct {
 	PacketNumber    protocol.PacketNumber
+	PacketType      protocol.PacketType
 	Frames          []wire.Frame
 	Length          protocol.ByteCount
 	EncryptionLevel protocol.EncryptionLevel

packet_packer.go

@@ -108,6 +108,10 @@ func (p *packetPacker) PackHandshakeRetransmission(packet *ackhandler.Packet) (*
 	if err != nil {
 		return nil, err
 	}
+	// make sure that the retransmission for an Initial packet is sent as an Initial packet
+	if packet.PacketType == protocol.PacketTypeInitial {
+		p.hasSentPacket = false
+	}
 	header := p.getHeader(packet.EncryptionLevel)
 	var frames []wire.Frame
 	if !p.version.UsesIETFFrameFormat() { // for gQUIC: pack a STOP_WAITING first

packet_packer_test.go

@@ -703,6 +703,21 @@ var _ = Describe("Packet packer", func() {
 			Expect(sf.DataLenPresent).To(BeTrue())
 		})
 
+		It("packs a retransmission for an Initial packet", func() {
+			packer.version = versionIETFFrames
+			packer.perspective = protocol.PerspectiveClient
+			packet := &ackhandler.Packet{
+				PacketType:      protocol.PacketTypeInitial,
+				EncryptionLevel: protocol.EncryptionUnencrypted,
+				Frames:          []wire.Frame{sf},
+			}
+			p, err := packer.PackHandshakeRetransmission(packet)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(p.frames).To(Equal([]wire.Frame{sf}))
+			Expect(p.encryptionLevel).To(Equal(protocol.EncryptionUnencrypted))
+			Expect(p.header.Type).To(Equal(protocol.PacketTypeInitial))
+		})
+
 		It("refuses to retransmit packets that were sent with forward-secure encryption", func() {
 			p := &ackhandler.Packet{
 				EncryptionLevel: protocol.EncryptionForwardSecure,