From 0f401b0b3785399fd40f5a9c3b40092ca8e3b950 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Sat, 10 Mar 2018 14:14:09 +0700
Subject: [PATCH] parse the max_packet_size in the TLS transport parameters

---
 internal/handshake/transport_parameter_test.go | 14 ++++++++++++++
 internal/handshake/transport_parameters.go     | 11 +++++++++++
 2 files changed, 25 insertions(+)

diff --git a/internal/handshake/transport_parameter_test.go b/internal/handshake/transport_parameter_test.go
index 87a3c888..431da748 100644
--- a/internal/handshake/transport_parameter_test.go
+++ b/internal/handshake/transport_parameter_test.go
@@ -132,6 +132,7 @@ var _ = Describe("Transport Parameters", func() {
 					initialMaxStreamIDBiDiParameterID: {0x33, 0x44, 0x55, 0x66},
 					initialMaxStreamIDUniParameterID:  {0x44, 0x55, 0x66, 0x77},
 					idleTimeoutParameterID:            {0x13, 0x37},
+					maxPacketSizeParameterID:          {0x73, 0x31},
 				}
 			})
 			It("reads parameters", func() {
@@ -143,6 +144,7 @@ var _ = Describe("Transport Parameters", func() {
 				Expect(params.MaxUniStreamID).To(Equal(protocol.StreamID(0x44556677)))
 				Expect(params.IdleTimeout).To(Equal(0x1337 * time.Second))
 				Expect(params.OmitConnectionID).To(BeFalse())
+				Expect(params.MaxPacketSize).To(Equal(protocol.ByteCount(0x7331)))
 			})
 
 			It("saves if it should omit the connection ID", func() {
@@ -215,6 +217,18 @@ var _ = Describe("Transport Parameters", func() {
 				Expect(err).To(MatchError("wrong length for omit_connection_id: 1 (expected empty)"))
 			})
 
+			It("rejects the parameters if max_packet_size has the wrong length", func() {
+				parameters[maxPacketSizeParameterID] = []byte{0x11} // should be 2 bytes
+				_, err := readTransportParamters(paramsMapToList(parameters))
+				Expect(err).To(MatchError("wrong length for max_packet_size: 1 (expected 2)"))
+			})
+
+			It("rejects max_packet_sizes smaller than 1200 bytes", func() {
+				parameters[maxPacketSizeParameterID] = []byte{0x4, 0xaf} // 0x4af = 1199
+				_, err := readTransportParamters(paramsMapToList(parameters))
+				Expect(err).To(MatchError("invalid value for max_packet_size: 1199 (minimum 1200)"))
+			})
+
 			It("ignores unknown parameters", func() {
 				parameters[1337] = []byte{42}
 				_, err := readTransportParamters(paramsMapToList(parameters))
diff --git a/internal/handshake/transport_parameters.go b/internal/handshake/transport_parameters.go
index 22614375..8cd451a1 100644
--- a/internal/handshake/transport_parameters.go
+++ b/internal/handshake/transport_parameters.go
@@ -20,6 +20,8 @@ type TransportParameters struct {
 	StreamFlowControlWindow     protocol.ByteCount
 	ConnectionFlowControlWindow protocol.ByteCount
 
+	MaxPacketSize protocol.ByteCount
+
 	MaxBidiStreamID protocol.StreamID // only used for IETF QUIC
 	MaxUniStreamID  protocol.StreamID // only used for IETF QUIC
 	MaxStreams      uint32            // only used for gQUIC
@@ -137,6 +139,15 @@ func readTransportParamters(paramsList []transportParameter) (*TransportParamete
 				return nil, fmt.Errorf("wrong length for omit_connection_id: %d (expected empty)", len(p.Value))
 			}
 			params.OmitConnectionID = true
+		case maxPacketSizeParameterID:
+			if len(p.Value) != 2 {
+				return nil, fmt.Errorf("wrong length for max_packet_size: %d (expected 2)", len(p.Value))
+			}
+			maxPacketSize := protocol.ByteCount(binary.BigEndian.Uint16(p.Value))
+			if maxPacketSize < 1200 {
+				return nil, fmt.Errorf("invalid value for max_packet_size: %d (minimum 1200)", maxPacketSize)
+			}
+			params.MaxPacketSize = maxPacketSize
 		}
 	}