os: add ReadFile, WriteFile, CreateTemp (was TempFile), MkdirTemp (was TempDir) from io/ioutil

io/ioutil was a poorly defined collection of helpers.
Proposal #40025 moved out the generic I/O helpers to io.
This CL for proposal #42026 moves the OS-specific helpers to os,
making the entire io/ioutil package deprecated.

For #42026.

Change-Id: I018bcb2115ef2ff1bc7ca36a9247eda429af21ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/266364
Trust: Russ Cox <rsc@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>

1 files changed, 118 insertions, 0 deletions

diff --git a/src/os/tempfile.go b/src/os/tempfile.go
new file mode 100644
index 0000000000..2728485c32
--- /dev/null
+++ b/src/os/tempfile.go
@@ -0,0 +1,118 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"errors"
+	"strings"
+)
+
+// 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, TempFile 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 := strings.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, TempFile 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
+}