parse version negotiation packets

public_header.go

@@ -27,7 +27,8 @@ type PublicHeader struct {
 	TruncateConnectionID bool
 	PacketNumberLen      protocol.PacketNumberLen
 	PacketNumber         protocol.PacketNumber
-	VersionNumber        protocol.VersionNumber
+	VersionNumber        protocol.VersionNumber   // VersionNumber sent by the client
+	SupportedVersions    []protocol.VersionNumber // VersionNumbers sent by the server
 	DiversificationNonce []byte
 }
 
@@ -169,13 +170,27 @@ func ParsePublicHeader(b io.ByteReader, packetSentBy protocol.Perspective) (*Pub
 	}
 
 	// Version (optional)
-	if header.VersionFlag && !header.ResetFlag {
-		var versionTag uint32
-		versionTag, err = utils.ReadUint32(b)
-		if err != nil {
-			return nil, err
+	if !header.ResetFlag {
+		if header.VersionFlag {
+			if packetSentBy == protocol.PerspectiveClient {
+				var versionTag uint32
+				versionTag, err = utils.ReadUint32(b)
+				if err != nil {
+					return nil, err
+				}
+				header.VersionNumber = protocol.VersionTagToNumber(versionTag)
+			} else { // parse the version negotiaton packet
+				header.SupportedVersions = make([]protocol.VersionNumber, 0)
+				for {
+					var versionTag uint32
+					versionTag, err = utils.ReadUint32(b)
+					if err != nil {
+						break
+					}
+					header.SupportedVersions = append(header.SupportedVersions, protocol.VersionTagToNumber(versionTag))
+				}
+			}
 		}
-		header.VersionNumber = protocol.VersionTagToNumber(versionTag)
 	}
 
 	// Packet number

public_header_test.go

@@ -18,6 +18,7 @@ var _ = Describe("Public Header", func() {
 			Expect(hdr.ResetFlag).To(BeFalse())
 			Expect(hdr.ConnectionID).To(Equal(protocol.ConnectionID(0x4cfa9f9b668619f6)))
 			Expect(hdr.VersionNumber).To(Equal(protocol.Version34))
+			Expect(hdr.SupportedVersions).To(BeEmpty())
 			Expect(hdr.PacketNumber).To(Equal(protocol.PacketNumber(1)))
 			Expect(b.Len()).To(BeZero())
 		})
@@ -72,6 +73,15 @@ var _ = Describe("Public Header", func() {
 			Expect(err).To(MatchError("diversification nonces should only be sent by servers"))
 		})
 
+		It("parses version negotiation packets sent by the server", func() {
+			data := composeVersionNegotiation(0x1337)
+			hdr, err := ParsePublicHeader(bytes.NewReader(data), protocol.PerspectiveServer)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(hdr.VersionFlag).To(BeTrue())
+			Expect(hdr.VersionNumber).To(BeZero()) // unitialized
+			Expect(hdr.SupportedVersions).To(Equal(protocol.SupportedVersions))
+		})
+
 		Context("Packet Number lengths", func() {
 			It("accepts 1-byte packet numbers", func() {
 				b := bytes.NewReader([]byte{0x08, 0xf6, 0x19, 0x86, 0x66, 0x9b, 0x9f, 0xfa, 0x4c, 0xde})