util.go

package corral

import (
	"bufio"
	"encoding/base64"
	"fmt"
	"net"
	"os"
	"strings"
)

func readUptime() string {
	file, err := os.Open("/proc/uptime")
	if err != nil {
		return ""
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		text := scanner.Text()
		parts := strings.Split(text, " ")
		return base64.StdEncoding.EncodeToString([]byte(parts[0]))
	}
	return ""
}

const letterBytes = "abcdef0123456789-_"
const (
	letterIdxBits = 6                    // 6 bits to represent a letter index
	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
)

func randomName() string {
	sb := strings.Builder{}
	sb.Grow(10)
	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
	for i, cache, remain := 9, src.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = src.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			sb.WriteByte(letterBytes[idx])
			i--
		}
		cache >>= letterIdxBits
		remain--
	}

	return sb.String()
}

func selectIP() (string, error) {
	addrs, err := net.InterfaceAddrs()
	if err != nil {
		fmt.Printf("Unable to get interface addresses: %v", err)
		return "", err
	}

	for _, a := range addrs {
		if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
			if ipnet.IP.To4() != nil {
				return ipnet.IP.String(), nil
			}
		}
	}

	return "", fmt.Errorf("failed to find valid ip")
}