Make max datagram frame size configurable

config.go

@@ -101,6 +101,10 @@ func populateConfig(config *Config) *Config {
 	} else if maxIncomingUniStreams < 0 {
 		maxIncomingUniStreams = 0
 	}
+	maxDatagrameFrameSize := config.MaxDatagramFrameSize
+	if maxDatagrameFrameSize == 0 {
+		maxDatagrameFrameSize = int64(protocol.DefaultMaxDatagramFrameSize)
+	}
 
 	return &Config{
 		GetConfigForClient:               config.GetConfigForClient,
@@ -120,6 +124,7 @@ func populateConfig(config *Config) *Config {
 		MaxIncomingUniStreams:            maxIncomingUniStreams,
 		TokenStore:                       config.TokenStore,
 		EnableDatagrams:                  config.EnableDatagrams,
+		MaxDatagramFrameSize:             maxDatagrameFrameSize,
 		DisablePathMTUDiscovery:          config.DisablePathMTUDiscovery,
 		DisableVersionNegotiationPackets: config.DisableVersionNegotiationPackets,
 		Allow0RTT:                        config.Allow0RTT,

config_test.go

@@ -83,6 +83,8 @@ var _ = Describe("Config", func() {
 				f.Set(reflect.ValueOf(time.Second))
 			case "EnableDatagrams":
 				f.Set(reflect.ValueOf(true))
+			case "MaxDatagramFrameSize":
+				f.Set(reflect.ValueOf(int64(1200)))
 			case "DisableVersionNegotiationPackets":
 				f.Set(reflect.ValueOf(true))
 			case "DisablePathMTUDiscovery":
@@ -175,6 +177,7 @@ var _ = Describe("Config", func() {
 			Expect(c.MaxIncomingUniStreams).To(BeEquivalentTo(protocol.DefaultMaxIncomingUniStreams))
 			Expect(c.DisableVersionNegotiationPackets).To(BeFalse())
 			Expect(c.DisablePathMTUDiscovery).To(BeFalse())
+			Expect(c.MaxDatagramFrameSize).To(BeEquivalentTo(protocol.DefaultMaxDatagramFrameSize))
 			Expect(c.GetConfigForClient).To(BeNil())
 		})
 

connection.go

@@ -317,7 +317,7 @@ var newConnection = func(
 		RetrySourceConnectionID:         retrySrcConnID,
 	}
 	if s.config.EnableDatagrams {
-		params.MaxDatagramFrameSize = protocol.MaxDatagramFrameSize
+		params.MaxDatagramFrameSize = protocol.ByteCount(s.config.MaxDatagramFrameSize)
 	} else {
 		params.MaxDatagramFrameSize = protocol.InvalidByteCount
 	}
@@ -430,7 +430,7 @@ var newClientConnection = func(
 		InitialSourceConnectionID:      srcConnID,
 	}
 	if s.config.EnableDatagrams {
-		params.MaxDatagramFrameSize = protocol.MaxDatagramFrameSize
+		params.MaxDatagramFrameSize = protocol.ByteCount(s.config.MaxDatagramFrameSize)
 	} else {
 		params.MaxDatagramFrameSize = protocol.InvalidByteCount
 	}
@@ -1493,7 +1493,7 @@ func (s *connection) handleAckFrame(frame *wire.AckFrame, encLevel protocol.Encr
 }
 
 func (s *connection) handleDatagramFrame(f *wire.DatagramFrame) error {
-	if f.Length(s.version) > protocol.MaxDatagramFrameSize {
+	if f.Length(s.version) > protocol.ByteCount(s.config.MaxDatagramFrameSize) {
 		return &qerr.TransportError{
 			ErrorCode:    qerr.ProtocolViolation,
 			ErrorMessage: "DATAGRAM frame too large",

interface.go

@@ -322,7 +322,9 @@ type Config struct {
 	Allow0RTT bool
 	// Enable QUIC datagram support (RFC 9221).
 	EnableDatagrams bool
-	Tracer          func(context.Context, logging.Perspective, ConnectionID) logging.ConnectionTracer
+	// Maximum size of QUIC datagram frames (RFC 9221).
+	MaxDatagramFrameSize int64
+	Tracer               func(context.Context, logging.Perspective, ConnectionID) logging.ConnectionTracer
 }
 
 type ClientHelloInfo struct {

internal/protocol/params.go

@@ -132,9 +132,9 @@ const MaxPostHandshakeCryptoFrameSize = 1000
 // but must ensure that a maximum size ACK frame fits into one packet.
 const MaxAckFrameSize ByteCount = 1000
 
-// MaxDatagramFrameSize is the maximum size of a DATAGRAM frame (RFC 9221).
+// DefaultMaxDatagramFrameSize is the maximum size of a DATAGRAM frame (RFC 9221).
 // The size is chosen such that a DATAGRAM frame fits into a QUIC packet.
-const MaxDatagramFrameSize ByteCount = 1200
+const DefaultMaxDatagramFrameSize ByteCount = 1200
 
 // DatagramRcvQueueLen is the length of the receive queue for DATAGRAM frames (RFC 9221)
 const DatagramRcvQueueLen = 128