Add safe rename functions at fs level

pkg/fs/fs_test.go

@@ -0,0 +1,130 @@
+package fs_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/influxdata/influxdb/pkg/fs"
+)
+
+func TestRenameFileWithReplacement(t *testing.T) {
+	t.Run("exists", func(t *testing.T) {
+		oldpath := MustCreateTempFile()
+		newpath := MustCreateTempFile()
+		defer MustRemoveAll(oldpath)
+		defer MustRemoveAll(newpath)
+
+		oldContents := MustReadAllFile(oldpath)
+		newContents := MustReadAllFile(newpath)
+
+		if got, exp := oldContents, oldpath; got != exp {
+			t.Fatalf("got contents %q, expected %q", got, exp)
+		} else if got, exp := newContents, newpath; got != exp {
+			t.Fatalf("got contents %q, expected %q", got, exp)
+		}
+
+		if err := fs.RenameFileWithReplacement(oldpath, newpath); err != nil {
+			t.Fatalf("ReplaceFileIfExists returned an error: %s", err)
+		}
+
+		if err := fs.SyncDir(filepath.Dir(oldpath)); err != nil {
+			panic(err)
+		}
+
+		// Contents of newpath will now be equivalent to oldpath' contents.
+		newContents = MustReadAllFile(newpath)
+		if newContents != oldContents {
+			t.Fatalf("contents for files differ: %q versus %q", newContents, oldContents)
+		}
+
+		// oldpath will be removed.
+		if MustFileExists(oldpath) {
+			t.Fatalf("file %q still exists, but it shouldn't", oldpath)
+		}
+	})
+
+	t.Run("not exists", func(t *testing.T) {
+		oldpath := MustCreateTempFile()
+		defer MustRemoveAll(oldpath)
+
+		oldContents := MustReadAllFile(oldpath)
+		if got, exp := oldContents, oldpath; got != exp {
+			t.Fatalf("got contents %q, expected %q", got, exp)
+		}
+
+		root := filepath.Dir(oldpath)
+		newpath := filepath.Join(root, "foo")
+		if err := fs.RenameFileWithReplacement(oldpath, newpath); err != nil {
+			t.Fatalf("ReplaceFileIfExists returned an error: %s", err)
+		}
+
+		if err := fs.SyncDir(filepath.Dir(oldpath)); err != nil {
+			panic(err)
+		}
+
+		// Contents of newpath will now be equivalent to oldpath's contents.
+		newContents := MustReadAllFile(newpath)
+		if newContents != oldContents {
+			t.Fatalf("contents for files differ: %q versus %q", newContents, oldContents)
+		}
+
+		// oldpath will be removed.
+		if MustFileExists(oldpath) {
+			t.Fatalf("file %q still exists, but it shouldn't", oldpath)
+		}
+	})
+}
+
+// MustCreateTempFile creates a temporary file returning the path to the file.
+//
+// MustCreateTempFile writes the absolute path to the file into the file itself.
+// It panics if there is an error.
+func MustCreateTempFile() string {
+	f, err := ioutil.TempFile("", "fs-test")
+	if err != nil {
+		panic(fmt.Sprintf("failed to create temp file: %v", err))
+	}
+
+	name := f.Name()
+	f.WriteString(name)
+	if err := f.Close(); err != nil {
+		panic(err)
+	}
+	return name
+}
+
+func MustRemoveAll(path string) {
+	if err := os.RemoveAll(path); err != nil {
+		panic(err)
+	}
+}
+
+// MustFileExists determines if a file exists, panicking if any error
+// (other than one associated with the file not existing) is returned.
+func MustFileExists(path string) bool {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true
+	} else if os.IsNotExist(err) {
+		return false
+	}
+	panic(err)
+}
+
+// MustReadAllFile reads the contents of path, panicking if there is an error.
+func MustReadAllFile(path string) string {
+	fd, err := os.Open(path)
+	if err != nil {
+		panic(err)
+	}
+	defer fd.Close()
+
+	data, err := ioutil.ReadAll(fd)
+	if err != nil {
+		panic(err)
+	}
+	return string(data)
+}

pkg/fs/fs_unix.go

@@ -3,10 +3,25 @@
 package fs
 
 import (
+	"fmt"
 	"os"
 	"syscall"
 )
 
+// A FileExistsError is returned when an operation cannot be completed due to a
+// file already existing.
+type FileExistsError struct {
+	path string
+}
+
+func newFileExistsError(path string) FileExistsError {
+	return FileExistsError{path: path}
+}
+
+func (e FileExistsError) Error() string {
+	return fmt.Sprintf("operation not allowed, file %q exists", e.path)
+}
+
 // SyncDir flushes any file renames to the filesystem.
 func SyncDir(dirName string) error {
 	// fsync the dir to flush the rename
@@ -39,3 +54,14 @@ func SyncDir(dirName string) error {
 func RenameFileWithReplacement(oldpath, newpath string) error {
 	return os.Rename(oldpath, newpath)
 }
+
+// RenameFile renames oldpath to newpath, returning an error if newpath already
+// exists. If this function returns successfully, the contents of newpath will
+// be identical to oldpath, and oldpath will be removed.
+func RenameFile(oldpath, newpath string) error {
+	if _, err := os.Stat(newpath); err == nil {
+		return newFileExistsError(newpath)
+	}
+
+	return os.Rename(oldpath, newpath)
+}

pkg/fs/fs_windows.go

@@ -21,3 +21,16 @@ func RenameFileWithReplacement(oldpath, newpath string) error {
 
 	return os.Rename(oldpath, newpath)
 }
+
+// RenameFile renames oldpath to newpath, returning an error if newpath already
+// exists. If this function returns successfully, the contents of newpath will
+// be identical to oldpath, and oldpath will be removed.
+func RenameFile(oldpath, newpath string) error {
+	if _, err := os.Stat(newpath); err == nil {
+		// os.Rename on Windows will return an error if the file exists, but it's
+		// preferable to keep the errors the same across platforms.
+		return newFileExistsError(newpath)
+	}
+
+	return os.Rename(oldpath, newpath)
+}