blob/fileblob: Add an option to avoid using os.TempDir for temp files

blob/fileblob/fileblob.go

@@ -218,6 +218,14 @@ type Options struct {
 	// (using os.MkdirAll).
 	CreateDir bool
 
+	// If true, don't use os.TempDir for temporary files, but instead place them
+	// next to the actual files. This may result in "stranded" temporary files
+	// (e.g., if the application is killed before the file cleanup runs).
+	//
+	// If your bucket directory is on a different mount than os.TempDir, you will
+	// need to set this to true, as os.Rename will fail across mount points.
+	NoTempDir bool
+
 	// Refers to the strategy for how to deal with metadata (such as blob.Attributes).
 	// For supported values please see the Metadata* constants.
 	// If left unchanged, 'MetadataInSidecar' will be used.
@@ -642,7 +650,7 @@ func (r *reader) As(i interface{}) bool {
 	return true
 }
 
-func createTemp(path string) (*os.File, error) {
+func createTemp(path string, noTempDir bool) (*os.File, error) {
 	// Use a custom createTemp function rather than os.CreateTemp() as
 	// os.CreateTemp() sets the permissions of the tempfile to 0600, rather than
 	// 0666, making it inconsistent with the directories and attribute files.
@@ -653,7 +661,13 @@ func createTemp(path string) (*os.File, error) {
 		// between each iteration to make a conflict unlikely. Using the full
 		// time lowers the chance of a collision with a file using a similar
 		// pattern, but has undefined behavior after the year 2262.
-		name := filepath.Join(os.TempDir(), filepath.Base(path)) + "." + strconv.FormatInt(time.Now().UnixNano(), 16) + ".tmp"
+		var name string
+		if noTempDir {
+			name = path
+		} else {
+			name = filepath.Join(os.TempDir(), filepath.Base(path))
+		}
+		name += "." + strconv.FormatInt(time.Now().UnixNano(), 16) + ".tmp"
 		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
 		if os.IsExist(err) {
 			if try++; try < 10000 {
@@ -674,7 +688,7 @@ func (b *bucket) NewTypedWriter(ctx context.Context, key string, contentType str
 	if err := os.MkdirAll(filepath.Dir(path), os.FileMode(0777)); err != nil {
 		return nil, err
 	}
-	f, err := createTemp(path)
+	f, err := createTemp(path, b.opts.NoTempDir)
 	if err != nil {
 		return nil, err
 	}

blob/fileblob/fileblob_test.go

@@ -39,12 +39,13 @@ type harness struct {
 	dir         string
 	prefix      string
 	metadataHow metadataOption
+	noTempDir   bool
 	server      *httptest.Server
 	urlSigner   URLSigner
 	closer      func()
 }
 
-func newHarness(ctx context.Context, t *testing.T, prefix string, metadataHow metadataOption) (drivertest.Harness, error) {
+func newHarness(ctx context.Context, t *testing.T, prefix string, metadataHow metadataOption, noTempDir bool) (drivertest.Harness, error) {
 	if metadataHow == MetadataDontWrite {
 		// Skip tests for if no metadata gets written.
 		// For these it is currently undefined whether any gets read (back).
@@ -64,7 +65,7 @@ func newHarness(ctx context.Context, t *testing.T, prefix string, metadataHow me
 			return nil, err
 		}
 	}
-	h := &harness{dir: dir, prefix: prefix, metadataHow: metadataHow}
+	h := &harness{dir: dir, prefix: prefix, metadataHow: metadataHow, noTempDir: noTempDir}
 
 	localServer := httptest.NewServer(http.HandlerFunc(h.serveSignedURL))
 	h.server = localServer
@@ -148,6 +149,7 @@ func (h *harness) MakeDriver(ctx context.Context) (driver.Bucket, error) {
 	opts := &Options{
 		URLSigner: h.urlSigner,
 		Metadata:  h.metadataHow,
+		NoTempDir: h.noTempDir,
 	}
 	drv, err := openBucket(h.dir, opts)
 	if err != nil {
@@ -171,22 +173,29 @@ func (h *harness) Close() {
 
 func TestConformance(t *testing.T) {
 	newHarnessNoPrefix := func(ctx context.Context, t *testing.T) (drivertest.Harness, error) {
-		return newHarness(ctx, t, "", MetadataInSidecar)
+		return newHarness(ctx, t, "", MetadataInSidecar, false)
 	}
 	drivertest.RunConformanceTests(t, newHarnessNoPrefix, []drivertest.AsTest{verifyAs{}})
 }
 
+func TestConformanceNoTempDir(t *testing.T) {
+	newHarnessNoTmpDir := func(ctx context.Context, t *testing.T) (drivertest.Harness, error) {
+		return newHarness(ctx, t, "", MetadataInSidecar, true)
+	}
+	drivertest.RunConformanceTests(t, newHarnessNoTmpDir, []drivertest.AsTest{verifyAs{}})
+}
+
 func TestConformanceWithPrefix(t *testing.T) {
 	const prefix = "some/prefix/dir/"
 	newHarnessWithPrefix := func(ctx context.Context, t *testing.T) (drivertest.Harness, error) {
-		return newHarness(ctx, t, prefix, MetadataInSidecar)
+		return newHarness(ctx, t, prefix, MetadataInSidecar, false)
 	}
 	drivertest.RunConformanceTests(t, newHarnessWithPrefix, []drivertest.AsTest{verifyAs{prefix: prefix}})
 }
 
 func TestConformanceSkipMetadata(t *testing.T) {
 	newHarnessSkipMetadata := func(ctx context.Context, t *testing.T) (drivertest.Harness, error) {
-		return newHarness(ctx, t, "", MetadataDontWrite)
+		return newHarness(ctx, t, "", MetadataDontWrite, false)
 	}
 	drivertest.RunConformanceTests(t, newHarnessSkipMetadata, []drivertest.AsTest{verifyAs{}})
 }