internal.go

package main

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"io/ioutil"
	"log"
	"math/big"
	"os"
	"os/exec"
	"strings"
	"time"
	"unicode"
)

const alphanum string = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

var (
	TimeoutErr = errors.New("Command timed out.")

	NotImplementedError = errors.New("not implemented yet")
)

// ReadLines reads contents from a file and splits them by new lines.
// A convenience wrapper to ReadLinesOffsetN(filename, 0, -1).
func ReadLines(filename string) ([]string, error) {
	return ReadLinesOffsetN(filename, 0, -1)
}

// ReadLines reads contents from file and splits them by new line.
// The offset tells at which line number to start.
// The count determines the number of lines to read (starting from offset):
//   n >= 0: at most n lines
//   n < 0: whole file
func ReadLinesOffsetN(filename string, offset uint, n int) ([]string, error) {
	f, err := os.Open(filename)
	if err != nil {
		return []string{""}, err
	}
	defer f.Close()

	var ret []string

	r := bufio.NewReader(f)
	for i := 0; i < n+int(offset) || n < 0; i++ {
		line, err := r.ReadString('\n')
		if err != nil {
			break
		}
		if i < int(offset) {
			continue
		}
		ret = append(ret, strings.Trim(line, "\n"))
	}

	return ret, nil
}

// RandomString returns a random string of alpha-numeric characters
func RandomString(n int) string {
	var bytes = make([]byte, n)
	rand.Read(bytes)
	for i, b := range bytes {
		bytes[i] = alphanum[b%byte(len(alphanum))]
	}
	return string(bytes)
}

// GetTLSConfig gets a tls.Config object from the given certs, key, and CA files.
// you must give the full path to the files.
// If all files are blank and InsecureSkipVerify=false, returns a nil pointer.
func GetTLSConfig(
	SSLCert, SSLKey, SSLCA string,
	InsecureSkipVerify bool,
) (*tls.Config, error) {
	if SSLCert == "" && SSLKey == "" && SSLCA == "" && !InsecureSkipVerify {
		return nil, nil
	}

	t := &tls.Config{
		InsecureSkipVerify: InsecureSkipVerify,
	}

	if SSLCA != "" {
		caCert, err := ioutil.ReadFile(SSLCA)
		if err != nil {
			return nil, errors.New(fmt.Sprintf("Could not load TLS CA: %s",
				err))
		}

		caCertPool := x509.NewCertPool()
		caCertPool.AppendCertsFromPEM(caCert)
		t.RootCAs = caCertPool
	}

	if SSLCert != "" && SSLKey != "" {
		cert, err := tls.LoadX509KeyPair(SSLCert, SSLKey)
		if err != nil {
			return nil, errors.New(fmt.Sprintf(
				"Could not load TLS client key/certificate from %s:%s: %s",
				SSLKey, SSLCert, err))
		}

		t.Certificates = []tls.Certificate{cert}
		t.BuildNameToCertificate()
	}

	// will be nil by default if nothing is provided
	return t, nil
}

// SnakeCase converts the given string to snake case following the Golang format:
// acronyms are converted to lower-case and preceded by an underscore.
func SnakeCase(in string) string {
	runes := []rune(in)
	length := len(runes)

	var out []rune
	for i := 0; i < length; i++ {
		if i > 0 && unicode.IsUpper(runes[i]) && ((i+1 < length && unicode.IsLower(runes[i+1])) || unicode.IsLower(runes[i-1])) {
			out = append(out, '_')
		}
		out = append(out, unicode.ToLower(runes[i]))
	}

	return string(out)
}

// CombinedOutputTimeout runs the given command with the given timeout and
// returns the combined output of stdout and stderr.
// If the command times out, it attempts to kill the process.
func CombinedOutputTimeout(c *exec.Cmd, timeout time.Duration) ([]byte, error) {
	var b bytes.Buffer
	c.Stdout = &b
	c.Stderr = &b
	if err := c.Start(); err != nil {
		return nil, err
	}
	err := WaitTimeout(c, timeout)
	return b.Bytes(), err
}

// RunTimeout runs the given command with the given timeout.
// If the command times out, it attempts to kill the process.
func RunTimeout(c *exec.Cmd, timeout time.Duration) error {
	if err := c.Start(); err != nil {
		return err
	}
	return WaitTimeout(c, timeout)
}

// WaitTimeout waits for the given command to finish with a timeout.
// It assumes the command has already been started.
// If the command times out, it attempts to kill the process.
func WaitTimeout(c *exec.Cmd, timeout time.Duration) error {
	timer := time.NewTimer(timeout)
	done := make(chan error)
	go func() { done <- c.Wait() }()
	select {
	case err := <-done:
		timer.Stop()
		return err
	case <-timer.C:
		if err := c.Process.Kill(); err != nil {
			log.Printf("E! FATAL error killing process: %s", err)
			return err
		}
		// wait for the command to return after killing it
		<-done
		return TimeoutErr
	}
}

// RandomSleep will sleep for a random amount of time up to max.
// If the shutdown channel is closed, it will return before it has finished
// sleeping.
func RandomSleep(max time.Duration, shutdown chan struct{}) {
	if max == 0 {
		return
	}
	maxSleep := big.NewInt(max.Nanoseconds())

	var sleepns int64
	if j, err := rand.Int(rand.Reader, maxSleep); err == nil {
		sleepns = j.Int64()
	}

	t := time.NewTimer(time.Nanosecond * time.Duration(sleepns))
	select {
	case <-t.C:
		return
	case <-shutdown:
		t.Stop()
		return
	}
}