set the UDP receive buffer size on Windows

conn_generic.go

@@ -1,4 +1,4 @@
-// +build !darwin,!linux
+// +build !darwin,!linux,!windows
 
 package quic
 

conn_windows.go

@@ -0,0 +1,37 @@
+// +build windows
+
+package quic
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+func newConn(c net.PacketConn) (connection, error) {
+	return &basicConn{PacketConn: c}, nil
+}
+
+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 = windows.GetsockoptInt(windows.Handle(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
+	}); err != nil {
+		return 0, err
+	}
+	return size, serr
+}

go.mod

@@ -17,6 +17,7 @@ require (
 	golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9
 	golang.org/x/net v0.0.0-20200707034311-ab3426394381
 	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
+	golang.org/x/sys v0.0.0-20200519105757-fe76b779f299
 	google.golang.org/protobuf v1.23.0
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 )