Source: tempfile.go in package os


package os

import "errors"

fastrand provided by runtime. 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.

func fastrand() uint32

func nextRandom() string {
	return uitoa(uint(fastrand()))
}

CreateTemp creates a new temporary file in the directory dir, opens the file for reading and writing, and returns the resulting 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, CreateTemp uses the default directory for temporary files, as returned by TempDir. Multiple programs or goroutines calling CreateTemp simultaneously will not choose the same file. The caller can use the file's Name method to find the pathname of the file. It is the caller's responsibility to remove the file when it is no longer needed.

func CreateTemp(dir, pattern string) (*File, error) {
	if dir == "" {
		dir = TempDir()
	}

	prefix, suffix, err := prefixAndSuffix(pattern)
	if err != nil {
		return nil, &PathError{Op: "createtemp", Path: pattern, Err: err}
	}
	prefix = joinPath(dir, prefix)

	try := 0
	for {
		name := prefix + nextRandom() + suffix
		f, err := OpenFile(name, O_RDWR|O_CREATE|O_EXCL, 0600)
		if IsExist(err) {
			if try++; try < 10000 {
				continue
			}
			return nil, &PathError{Op: "createtemp", Path: dir + string(PathSeparator) + prefix + "*" + suffix, Err: ErrExist}
		}
		return f, err
	}
}

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) {
	for i := 0; i < len(pattern); i++ {
		if IsPathSeparator(pattern[i]) {
			return "", "", errPatternHasSeparator
		}
	}
	if pos := lastIndex(pattern, '*'); pos != -1 {
		prefix, suffix = pattern[:pos], pattern[pos+1:]
	} else {
		prefix = pattern
	}
	return prefix, suffix, nil
}

MkdirTemp creates a new temporary directory in the directory dir and returns the pathname of the new directory. The new directory's name is generated by adding a random string to the end of pattern. If pattern includes a "*", the random string replaces the last "*" instead. If dir is the empty string, MkdirTemp uses the default directory for temporary files, as returned by TempDir. Multiple programs or goroutines calling MkdirTemp simultaneously will not choose the same directory. It is the caller's responsibility to remove the directory when it is no longer needed.

func MkdirTemp(dir, pattern string) (string, error) {
	if dir == "" {
		dir = TempDir()
	}

	prefix, suffix, err := prefixAndSuffix(pattern)
	if err != nil {
		return "", &PathError{Op: "mkdirtemp", Path: pattern, Err: err}
	}
	prefix = joinPath(dir, prefix)

	try := 0
	for {
		name := prefix + nextRandom() + suffix
		err := Mkdir(name, 0700)
		if err == nil {
			return name, nil
		}
		if IsExist(err) {
			if try++; try < 10000 {
				continue
			}
			return "", &PathError{Op: "mkdirtemp", Path: dir + string(PathSeparator) + prefix + "*" + suffix, Err: ErrExist}
		}
		if IsNotExist(err) {
			if _, err := Stat(dir); IsNotExist(err) {
				return "", err
			}
		}
		return "", err
	}
}

func joinPath(dir, name string) string {
	if len(dir) > 0 && IsPathSeparator(dir[len(dir)-1]) {
		return dir + name
	}
	return dir + string(PathSeparator) + name
}

LastIndexByte from the strings package.

func lastIndex(s string, sep byte) int {
	for i := len(s) - 1; i >= 0; i-- {
		if s[i] == sep {
			return i
		}
	}
	return -1