add a handshake test for post-quantum-size ClientHellos (#3759)

Post-quantum ClientHellos typically are larger than 1 MTU and will
therefore need to be split across multiple packets.

internal/wire/transport_parameter_test.go

@@ -125,6 +125,22 @@ var _ = Describe("Transport Parameters", func() {
 		Expect(p.MaxDatagramFrameSize).To(Equal(params.MaxDatagramFrameSize))
 	})
 
+	It("marshals additional transport parameters (used for testing large ClientHellos)", func() {
+		origAdditionalTransportParametersClient := AdditionalTransportParametersClient
+		defer func() {
+			AdditionalTransportParametersClient = origAdditionalTransportParametersClient
+		}()
+		AdditionalTransportParametersClient = map[uint64][]byte{1337: []byte("foobar")}
+
+		result := quicvarint.Append([]byte{}, 1337)
+		result = quicvarint.Append(result, 6)
+		result = append(result, []byte("foobar")...)
+
+		params := &TransportParameters{}
+		Expect(bytes.Contains(params.Marshal(protocol.PerspectiveClient), result)).To(BeTrue())
+		Expect(bytes.Contains(params.Marshal(protocol.PerspectiveServer), result)).To(BeFalse())
+	})
+
 	It("doesn't marshal a retry_source_connection_id, if no Retry was performed", func() {
 		data := (&TransportParameters{
 			StatelessResetToken:     &protocol.StatelessResetToken{},

internal/wire/transport_parameters.go

@@ -17,6 +17,12 @@ import (
 	"github.com/quic-go/quic-go/quicvarint"
 )
 
+// AdditionalTransportParametersClient are additional transport parameters that will be added
+// to the client's transport parameters.
+// This is not intended for production use, but _only_ to increase the size of the ClientHello beyond
+// the usual size of less than 1 MTU.
+var AdditionalTransportParametersClient map[uint64][]byte
+
 const transportParameterMarshalingVersion = 1
 
 func init() {
@@ -402,6 +408,15 @@ func (p *TransportParameters) Marshal(pers protocol.Perspective) []byte {
 	if p.MaxDatagramFrameSize != protocol.InvalidByteCount {
 		b = p.marshalVarintParam(b, maxDatagramFrameSizeParameterID, uint64(p.MaxDatagramFrameSize))
 	}
+
+	if pers == protocol.PerspectiveClient && len(AdditionalTransportParametersClient) > 0 {
+		for k, v := range AdditionalTransportParametersClient {
+			b = quicvarint.Append(b, k)
+			b = quicvarint.Append(b, uint64(len(v)))
+			b = append(b, v...)
+		}
+	}
+
 	return b
 }