increase UDP receive buffer size

conn_notwindows.go

@@ -0,0 +1,31 @@
+// +build !windows
+
+package quic
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"syscall"
+)
+
+func inspectReadBuffer(c net.PacketConn) (int, error) {
+	conn, ok := c.(interface {
+		SyscallConn() (syscall.RawConn, error)
+	})
+	if !ok {
+		return 0, errors.New("doesn't have a SyscallConn")
+	}
+	rawConn, err := conn.SyscallConn()
+	if err != nil {
+		return 0, fmt.Errorf("couldn't get syscall.RawConn: %w", err)
+	}
+	var size int
+	var serr error
+	if err := rawConn.Control(func(fd uintptr) {
+		size, serr = syscall.GetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
+	}); err != nil {
+		return 0, err
+	}
+	return size, serr
+}

conn_windows.go

@@ -7,3 +7,7 @@ import "net"
 func newConn(c net.PacketConn) (connection, error) {
 	return &basicConn{PacketConn: c}, nil
 }
+
+func inspectReadBuffer(net.PacketConn) (int, error) {
+	return 0, nil
+}

internal/protocol/params.go

@@ -2,6 +2,9 @@ package protocol
 
 import "time"
 
+// DesiredReceiveBufferSize is the kernel UDP receive buffer size that we'd like to use.
+const DesiredReceiveBufferSize = (1 << 20) * 2 // 2 MB
+
 // MaxPacketSizeIPv4 is the maximum packet size that we use for sending IPv4 packets.
 const MaxPacketSizeIPv4 = 1252
 

packet_handler_map.go

@@ -6,6 +6,7 @@ import (
 	"crypto/sha256"
 	"fmt"
 	"hash"
+	"log"
 	"net"
 	"sync"
 	"time"
@@ -53,6 +54,40 @@ type packetHandlerMap struct {
 
 var _ packetHandlerManager = &packetHandlerMap{}
 
+func setReceiveBuffer(c net.PacketConn, logger utils.Logger) {
+	conn, ok := c.(interface{ SetReadBuffer(int) error })
+	if !ok {
+		logger.Debugf("Connection doesn't allow setting of receive buffer size")
+		return
+	}
+	size, err := inspectReadBuffer(c)
+	if err != nil {
+		log.Printf("Failed to determine receive buffer size: %s", err)
+		return
+	}
+	if size >= protocol.DesiredReceiveBufferSize {
+		logger.Debugf("Conn has receive buffer of %d kiB (wanted: at least %d kiB)", size/1024, protocol.DesiredReceiveBufferSize/1024)
+	}
+	if err := conn.SetReadBuffer(protocol.DesiredReceiveBufferSize); err != nil {
+		log.Printf("Failed to increase receive buffer size: %s\n", err)
+		return
+	}
+	newSize, err := inspectReadBuffer(c)
+	if err != nil {
+		log.Printf("Failed to determine receive buffer size: %s", err)
+		return
+	}
+	if newSize == size {
+		log.Printf("Failed to determine receive buffer size: %s", err)
+		return
+	}
+	if newSize < protocol.DesiredReceiveBufferSize {
+		log.Printf("Failed to sufficiently increase receive buffer size. Was: %d kiB, wanted: %d kiB, got: %d kiB.", size/1024, protocol.DesiredReceiveBufferSize/1024, newSize/1024)
+		return
+	}
+	logger.Debugf("Increased receive buffer size to %d kiB", newSize/1024)
+}
+
 func newPacketHandlerMap(
 	c net.PacketConn,
 	connIDLen int,
@@ -60,6 +95,7 @@ func newPacketHandlerMap(
 	tracer logging.Tracer,
 	logger utils.Logger,
 ) (packetHandlerManager, error) {
+	setReceiveBuffer(c, logger)
 	conn, err := wrapConn(c)
 	if err != nil {
 		return nil, err
@@ -81,7 +117,6 @@ func newPacketHandlerMap(
 	if logger.Debug() {
 		go m.logUsage()
 	}
-
 	return m, nil
 }