io/ioutil: add TempFile

R=r
CC=golang-dev
https://golang.org/cl/1472042

src/pkg/io/ioutil/Makefile

@@ -7,5 +7,6 @@ include ../../../Make.$(GOARCH)
 TARG=io/ioutil
 GOFILES=\
 	ioutil.go\
+	tempfile.go\
 
 include ../../../Make.pkg

src/pkg/io/ioutil/tempfile.go

+// 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 ioutil
+
+import (
+	"os"
+	"strconv"
+)
+
+// Random number state, accessed without lock; racy but harmless.
+// 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
+
+func reseed() uint32 {
+	sec, nsec, _ := os.Time()
+	return uint32(sec*1e9 + nsec + int64(os.Getpid()))
+}
+
+func nextSuffix() string {
+	r := rand
+	if r == 0 {
+		r = reseed()
+	}
+	r = r*1664525 + 1013904223 // constants from Numerical Recipes
+	rand = r
+	return strconv.Itoa(int(1e9 + r%1e9))[1:]
+}
+
+// TempFile creates a new temporary file in the directory dir
+// with a name beginning with prefix, opens the file for reading
+// and writing, and returns the resulting *os.File.
+// If dir is the empty string, TempFile uses the value of the
+// environment variable $TMPDIR or, if that is empty,/tmp.
+// Multiple programs calling TempFile simultaneously
+// will not choose the same file.  The caller can use f.Name()
+// to find the name of the file.  It is the caller's responsibility to
+// remove the file when no longer needed.
+func TempFile(dir, prefix string) (f *os.File, err os.Error) {
+	if dir == "" {
+		dir = os.Getenv("TMPDIR")
+		if dir == "" {
+			dir = "/tmp"
+		}
+	}
+
+	nconflict := 0
+	for i := 0; i < 10000; i++ {
+		name := dir + "/" + prefix + nextSuffix()
+		f, err = os.Open(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+		if pe, ok := err.(*os.PathError); ok && pe.Error == os.EEXIST {
+			if nconflict++; nconflict > 10 {
+				rand = reseed()
+			}
+			continue
+		}
+		break
+	}
+	return
+}

src/pkg/io/ioutil/tempfile_test.go

+// 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 ioutil_test
+
+import (
+	. "io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestTempFile(t *testing.T) {
+	f, err := TempFile("/_not_exists_", "foo")
+	if f != nil || err == nil {
+		t.Errorf("TempFile(`/_not_exists_`, `foo`) = %v, %v", f, err)
+	}
+
+	f, err = TempFile("/tmp", "ioutil_test")
+	if f == nil || err != nil {
+		t.Errorf("TempFile(`/tmp`, `ioutil_test`) = %v, %v", f, err)
+	}
+	re := testing.MustCompile("^/tmp/ioutil_test[0-9]+$")
+	if !re.MatchString(f.Name()) {
+		t.Fatalf("TempFile(`/tmp`, `ioutil_test`) created bad name %s", f.Name())
+	}
+	os.Remove(f.Name())
+	f.Close()
+}