util_windows.go

// +build windows

package flatfs

import (
	"bytes"
	"io/ioutil"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	goissue34681 "github.com/alexbrainman/goissue34681"
)

var tmpRand uint32
var randmu sync.Mutex

func reseed() uint32 {
	return uint32(time.Now().UnixNano() + int64(os.Getpid()))
}

func nextRandom() string {
	randmu.Lock()
	r := tmpRand
	if r == 0 {
		r = reseed()
	}
	r = r*1664525 + 1013904223 // constants from Numerical Recipes
	tmpRand = r
	randmu.Unlock()
	return strconv.Itoa(int(1e9 + r%1e9))[1:]
}

func prefixAndSuffix(pattern string) (prefix, suffix string) {
	if pos := strings.LastIndex(pattern, "*"); pos != -1 {
		prefix, suffix = pattern[:pos], pattern[pos+1:]
	} else {
		prefix = pattern
	}
	return
}

func tempFile(dir, pattern string) (f *os.File, err error) {
	if dir == "" {
		dir = os.TempDir()
	}

	prefix, suffix := prefixAndSuffix(pattern)

	nconflict := 0
	for i := 0; i < 10000; i++ {
		name := filepath.Join(dir, prefix+nextRandom()+suffix)
		f, err = goissue34681.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
		if os.IsExist(err) {
			if nconflict++; nconflict > 10 {
				randmu.Lock()
				tmpRand = reseed()
				randmu.Unlock()
			}
			continue
		}
		break
	}
	return
}

func readFile(filename string) ([]byte, error) {
	f, err := goissue34681.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	// It's a good but not certain bet that FileInfo will tell us exactly how much to
	// read, so let's try it but be prepared for the answer to be wrong.
	var n int64 = bytes.MinRead

	if fi, err := f.Stat(); err == nil {
		// As initial capacity for readAll, use Size + a little extra in case Size
		// is zero, and to avoid another allocation after Read has filled the
		// buffer. The readAll call will read into its allocated internal buffer
		// cheaply. If the size was wrong, we'll either waste some space off the end
		// or reallocate as needed, but in the overwhelmingly common case we'll get
		// it just right.
		if size := fi.Size() + bytes.MinRead; size > n {
			n = size
		}
	}

	return ioutil.ReadAll(f)
}