You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: route.go
    path of file: ./repos/gccrs/libgo/go/golang.org/x/net/route
    
    the code of the file until where you have to start completion: // Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build darwin || dragonfly || freebsd || netbsd || openbsd
// +build darwin dragonfly freebsd netbsd openbsd

// Package route provides basic functions for the manipulation of
// packet routing facilities on BSD variants.
//
// The package supports any version of Darwin, any version of
// DragonFly BSD, FreeBSD 7 and above, NetBSD 6 and above, and OpenBSD
//
    
func FetchRIB(af int, typ RIBType, arg int) ([]byte, error) {
	try := 0
	for {
		try++
		mib := [6]int32{sysCTL_NET, sysAF_ROUTE, 0, int32(af), int32(typ), int32(arg)}
		n := uintptr(0)
		if err := sysctl(mib[:], nil, &n, nil, 0); err != nil {
			return nil, os.NewSyscallError("sysctl", err)
		}
		if n == 0 {
			return nil, nil
		}
		b := make([]byte, n)
		if err := sysctl(mib[:], &b[0], &n, nil, 0); err != nil {
			// If the sysctl failed because the data got larger
			// between the two sysctl calls, try a few times
			// before failing. (golang.org/issue/45736).
			const maxTries = 3
			if err == syscall.ENOMEM && try < maxTries {
				continue
			}
			return nil, os.NewSyscallError("sysctl", err)
		}
		return b[:n], nil
	}
}