io/ioutil: support predictable prefix,suffix for TempDir with *

Allow TempDir to create directories with predictable
prefixes and suffixes, separated by the last "*", for example:
    "prefix*suffix"
will now expand to
    "prefix" + <RANDOM_VALUE> + "suffix"

RELNOTE=yes

Fixes #33805.

Change-Id: I85fa73ae6a684ce820d1810c82a60765eb9c4a42
Reviewed-on: https://go-review.googlesource.com/c/go/+/198488
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/io/ioutil/example_test.go

@@ -53,6 +53,29 @@ func ExampleTempDir() {
 	}
 }
 
+func ExampleTempDir_suffix() {
+	parentDir := os.TempDir()
+	logsDir, err := ioutil.TempDir(parentDir, "*-logs")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer os.RemoveAll(logsDir) // clean up
+
+	// Logs can be cleaned out earlier if needed by searching
+	// for all directories whose suffix ends in *-logs.
+	globPattern := filepath.Join(parentDir, "*-logs")
+	matches, err := filepath.Glob(globPattern)
+	if err != nil {
+		log.Fatalf("Failed to match %q: %v", globPattern, err)
+	}
+
+	for _, match := range matches {
+		if err := os.RemoveAll(match); err != nil {
+			log.Printf("Failed to remove %q: %v", match, err)
+		}
+	}
+}
+
 func ExampleTempFile() {
 	content := []byte("temporary file's content")
 	tmpfile, err := ioutil.TempFile("", "example")

src/io/ioutil/tempfile.go

@@ -52,12 +52,7 @@ func TempFile(dir, pattern string) (f *os.File, err error) {
 		dir = os.TempDir()
 	}
 
-	var prefix, suffix string
-	if pos := strings.LastIndex(pattern, "*"); pos != -1 {
-		prefix, suffix = pattern[:pos], pattern[pos+1:]
-	} else {
-		prefix = pattern
-	}
+	prefix, suffix := prefixAndSuffix(pattern)
 
 	nconflict := 0
 	for i := 0; i < 10000; i++ {
@@ -76,21 +71,36 @@ func TempFile(dir, pattern string) (f *os.File, err error) {
 	return
 }
 
-// TempDir creates a new temporary directory in the directory dir
-// with a name beginning with prefix and returns the path of the
-// new directory. If dir is the empty string, TempDir uses the
+// 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) {
+	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, prefix string) (name string, err error) {
+func TempDir(dir, pattern string) (name string, err error) {
 	if dir == "" {
 		dir = os.TempDir()
 	}
 
+	prefix, suffix := prefixAndSuffix(pattern)
+
 	nconflict := 0
 	for i := 0; i < 10000; i++ {
-		try := filepath.Join(dir, prefix+nextRandom())
+		try := filepath.Join(dir, prefix+nextRandom()+suffix)
 		err = os.Mkdir(try, 0700)
 		if os.IsExist(err) {
 			if nconflict++; nconflict > 10 {

src/io/ioutil/tempfile_test.go

@@ -54,18 +54,47 @@ func TestTempDir(t *testing.T) {
 		t.Errorf("TempDir(`/_not_exists_`, `foo`) = %v, %v", name, err)
 	}
 
-	dir := os.TempDir()
-	name, err = TempDir(dir, "ioutil_test")
-	if name == "" || err != nil {
-		t.Errorf("TempDir(dir, `ioutil_test`) = %v, %v", name, err)
+	tests := []struct {
+		pattern                string
+		wantPrefix, wantSuffix string
+	}{
+		{"ioutil_test", "ioutil_test", ""},
+		{"ioutil_test*", "ioutil_test", ""},
+		{"ioutil_test*xyz", "ioutil_test", "xyz"},
 	}
-	if name != "" {
-		os.Remove(name)
-		re := regexp.MustCompile("^" + regexp.QuoteMeta(filepath.Join(dir, "ioutil_test")) + "[0-9]+$")
+
+	dir := os.TempDir()
+
+	runTestTempDir := func(t *testing.T, pattern, wantRePat string) {
+		name, err := TempDir(dir, pattern)
+		if name == "" || err != nil {
+			t.Fatalf("TempDir(dir, `ioutil_test`) = %v, %v", name, err)
+		}
+		defer os.Remove(name)
+
+		re := regexp.MustCompile(wantRePat)
 		if !re.MatchString(name) {
-			t.Errorf("TempDir(`"+dir+"`, `ioutil_test`) created bad name %s", name)
+			t.Errorf("TempDir(%q, %q) created bad name\n\t%q\ndid not match pattern\n\t%q", dir, pattern, name, wantRePat)
 		}
 	}
+
+	for _, tt := range tests {
+		t.Run(tt.pattern, func(t *testing.T) {
+			wantRePat := "^" + regexp.QuoteMeta(filepath.Join(dir, tt.wantPrefix)) + "[0-9]+" + regexp.QuoteMeta(tt.wantSuffix) + "$"
+			runTestTempDir(t, tt.pattern, wantRePat)
+		})
+	}
+
+	// Separately testing "*xyz" (which has no prefix). That is when constructing the
+	// pattern to assert on, as in the previous loop, using filepath.Join for an empty
+	// prefix filepath.Join(dir, ""), produces the pattern:
+	//     ^<DIR>[0-9]+xyz$
+	// yet we just want to match
+	//     "^<DIR>/[0-9]+xyz"
+	t.Run("*xyz", func(t *testing.T) {
+		wantRePat := "^" + regexp.QuoteMeta(filepath.Join(dir)) + regexp.QuoteMeta(string(filepath.Separator)) + "[0-9]+xyz$"
+		runTestTempDir(t, "*xyz", wantRePat)
+	})
 }
 
 // test that we return a nice error message if the dir argument to TempDir doesn't