restore Windows compatibility (#860) (#861)

pkg/readbuffer/read_buffer.go

@@ -0,0 +1,13 @@
+// Package readbuffer contains a function to get the read buffer size of a socket.
+package readbuffer
+
+import (
+	"net"
+	"syscall"
+)
+
+// PacketConn is a packet connection.
+type PacketConn interface {
+	net.PacketConn
+	SyscallConn() (syscall.RawConn, error)
+}

pkg/readbuffer/read_buffer_lin.go

@@ -0,0 +1,31 @@
+//go:build linux
+
+package readbuffer
+
+import (
+	"syscall"
+)
+
+// ReadBuffer returns the read buffer size.
+func ReadBuffer(pc PacketConn) (int, error) {
+	rawConn, err := pc.SyscallConn()
+	if err != nil {
+		panic(err)
+	}
+
+	var v int
+	var err2 error
+
+	err = rawConn.Control(func(fd uintptr) {
+		v, err2 = syscall.GetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
+	})
+	if err != nil {
+		return 0, err
+	}
+
+	if err2 != nil {
+		return 0, err2
+	}
+
+	return v / 2, nil
+}

pkg/readbuffer/read_buffer_other.go

@@ -0,0 +1,10 @@
+//go:build !linux && !windows
+
+package readbuffer
+
+import "fmt"
+
+// ReadBuffer returns the read buffer size.
+func ReadBuffer(pc PacketConn) (int, error) {
+	return 0, fmt.Errorf("read buffer size is unimplemented on the current operating system")
+}

pkg/readbuffer/read_buffer_win.go

@@ -0,0 +1,29 @@
+//go:build windows
+
+package readbuffer
+
+import "syscall"
+
+// ReadBuffer returns the read buffer size.
+func ReadBuffer(pc PacketConn) (int, error) {
+	rawConn, err := pc.SyscallConn()
+	if err != nil {
+		panic(err)
+	}
+
+	var v int
+	var err2 error
+
+	err = rawConn.Control(func(fd uintptr) {
+		v, err2 = syscall.GetsockoptInt(syscall.Handle(fd), syscall.SOL_SOCKET, syscall.SO_RCVBUF)
+	})
+	if err != nil {
+		return 0, err
+	}
+
+	if err2 != nil {
+		return 0, err2
+	}
+
+	return v, nil
+}