fix: update atomic fs writer to delay tmp creation until Write

Signed-off-by: Evan Baker <[email protected]>

Author: rbtr

internal/fs/atomic.go

@@ -5,13 +5,16 @@ import (
 	"io/fs"
 	"os"
 	"path"
+	"sync"
 
 	"github.com/pkg/errors"
 )
 
 type AtomicWriter struct {
 	filename string
 	tempFile *os.File
+
+	lock sync.Mutex
 }
 
 var _ io.WriteCloser = &AtomicWriter{}
@@ -52,29 +55,39 @@ func NewAtomicWriter(filename string) (*AtomicWriter, error) {
 		}
 	}
 
-	tempFile, err := os.CreateTemp(path.Dir(filename), path.Base(filename)+"*.tmp")
-	if err != nil {
-		return nil, errors.Wrap(err, "unable to create temporary file")
-	}
-
-	return &AtomicWriter{filename: filename, tempFile: tempFile}, nil
+	return &AtomicWriter{filename: filename}, nil
 }
 
-// Close closes the temp file handle and moves the temp file to the final destination
+// Close closes the temp file handle and moves the temp file to the final destination.
+// Multiple calls to Close will have no effect after the first success.
 func (a *AtomicWriter) Close() error {
-	if err := a.tempFile.Close(); err != nil {
+	a.lock.Lock()
+	defer a.lock.Unlock()
+	if a.tempFile == nil {
+		return nil
+	}
+	if err := a.tempFile.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
 		return errors.Wrapf(err, "unable to close temp file %s", a.tempFile.Name())
 	}
-
 	if err := os.Rename(a.tempFile.Name(), a.filename); err != nil {
 		return errors.Wrapf(err, "unable to move temp file %s to destination %s", a.tempFile.Name(), a.filename)
 	}
-
+	a.tempFile = nil
 	return nil
 }
 
-// Write writes the buffer to the temp file. You must call Close() to complete the move from temp file to dest file
+// Write writes the buffer to the temp file. You must call Close() to complete the move from temp file to dest file.
+// Multiple calls to Write will append to the temp file.
 func (a *AtomicWriter) Write(p []byte) (int, error) {
+	a.lock.Lock()
+	defer a.lock.Unlock()
+	if a.tempFile == nil {
+		tempFile, err := os.CreateTemp("", path.Base(a.filename)+"*.tmp")
+		if err != nil {
+			return 0, errors.Wrap(err, "unable to create temporary file")
+		}
+		a.tempFile = tempFile
+	}
 	bs, err := a.tempFile.Write(p)
 	return bs, errors.Wrap(err, "unable to write to temp file")
 }