Source: tempfile.go in package io/ioutil


package ioutil

import (
	"errors"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"
)

Random number state. We generate random temporary file names so that there's a good chance the file doesn't exist yet - keeps the number of tries in TempFile to a minimum.

var rand uint32
var randmu sync.Mutex

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

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

TempFile creates a new temporary file in the directory dir, opens the file for reading and writing, and returns the resulting *os.File. The filename is generated by taking pattern and adding a random string to the end. If pattern includes a "*", the random string replaces the last "*". If dir is the empty string, TempFile uses the default directory for temporary files (see os.TempDir). Multiple programs calling TempFile simultaneously will not choose the same file. The caller can use f.Name() to find the pathname of the file. It is the caller's responsibility to remove the file when no longer needed.

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

	prefix, suffix, err := prefixAndSuffix(pattern)
	if err != nil {
		return
	}

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

var errPatternHasSeparator = errors.New("pattern contains path separator")

prefixAndSuffix splits pattern by the last wildcard "*", if applicable, returning prefix as the part before "*" and suffix as the part after "*".

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

TempDir creates a new temporary directory in the directory dir. The directory name is generated by taking pattern and applying a random string to the end. If pattern includes a "*", the random string replaces the last "*". TempDir returns the name of the new directory. If dir is the empty string, TempDir uses the default directory for temporary files (see os.TempDir). Multiple programs calling TempDir simultaneously will not choose the same directory. It is the caller's responsibility to remove the directory when no longer needed.

func TempDir(dir, pattern string) (name string, err error) {
	if dir == "" {
		dir = os.TempDir()
	}

	prefix, suffix, err := prefixAndSuffix(pattern)
	if err != nil {
		return
	}

	nconflict := 0
	for i := 0; i < 10000; i++ {
		try := filepath.Join(dir, prefix+nextRandom()+suffix)
		err = os.Mkdir(try, 0700)
		if os.IsExist(err) {
			if nconflict++; nconflict > 10 {
				randmu.Lock()
				rand = reseed()
				randmu.Unlock()
			}
			continue
		}
		if os.IsNotExist(err) {
			if _, err := os.Stat(dir); os.IsNotExist(err) {
				return "", err
			}
		}
		if err == nil {
			name = try
		}
		break
	}
	return