package net

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
)

// Configure the ARP cache parameters for the given interface.  This
// makes containers react more quickly to a change in the MAC address
// associated with an IP address.
func configureARPCache(procPath, name string) error {
	if err := sysctl(procPath, fmt.Sprintf("net/ipv4/neigh/%s/base_reachable_time", name), "5"); err != nil {
		return err
	}
	if err := sysctl(procPath, fmt.Sprintf("net/ipv4/neigh/%s/delay_first_probe_time", name), "2"); err != nil {
		return err
	}
	return sysctl(procPath, fmt.Sprintf("net/ipv4/neigh/%s/ucast_solicit", name), "1")
}

func sysctl(procPath, variable, value string) error {
	f, err := os.OpenFile(filepath.Join(procPath, "/sys/", variable), os.O_WRONLY, 0)
	if err != nil {
		return err
	}

	n, err := io.WriteString(f, value)
	if err != nil {
		return err
	}
	if n < len(value) {
		return io.ErrShortWrite
	}

	err = f.Close()
	if err != nil {
		return err
	}

	return nil
}

func sysctlIfExists(procPath, variable, value string) error {
	err := sysctl(procPath, variable, value)
	if err != nil && os.IsNotExist(err) {
		err = nil // ignore 'not found' errors
	}
	return err
}