decode record_size_limit extension

clienthello/client_hello_parser.go

@@ -415,6 +415,12 @@ func (m *ClientHelloMsg) Unmarshal(data []byte) bool {
 				extension.Data.CertificateCompressionAlgos = append(
 					extension.Data.CertificateCompressionAlgos, algo)
 			}
+		case extensionRecordSizeLimit:
+			// Record Size Limit
+			// RFC 8449
+			if !extData.ReadUint16(&extension.Data.RecordSizeLimit) {
+				return false
+			}
 		// Draft extensions (not IANA assigned)
 		case extensionApplicationSettings:
 			// Application-Layer Protocol Settings

clienthello/extensions.go

@@ -39,6 +39,7 @@ const (
 	extensionExtendedMasterSecret    uint16 = 23
 	extensionTokenBinding            uint16 = 24
 	extensionCompressCertificate     uint16 = 27
+	extensionRecordSizeLimit         uint16 = 28
 	extensionSessionTicket           uint16 = 35
 	extensionPreSharedKey            uint16 = 41
 	extensionEarlyData               uint16 = 42
@@ -86,6 +87,7 @@ type ExtensionData struct {
 	PSKModes                     []PSKMode         `json:"psk_modes,omitempty"`
 	PSKIdentities                []PSKIdentity     `json:"psk_identities,omitempty"`
 	PSKBinders                   []byteSlice       `json:"psk_binders,omitempty"`
+	RecordSizeLimit              uint16            `json:"record_size_limit,omitempty"`
 	Length                       uint16            `json:"length,omitempty"` // padding
 }