chore: Improve error messages in SaveFileToStorage

ctx.go

@@ -517,9 +517,13 @@
 
 // SaveFileToStorage saves any multipart file to an external storage system.
 func (c *DefaultCtx) SaveFileToStorage(fileheader *multipart.FileHeader, path string, storage Storage) error {
+	if fileheader == nil {
+		return ErrFileHeaderNil
+	}
+
 	file, err := fileheader.Open()
 	if err != nil {
-		return fmt.Errorf("failed to open: %w", err)
+		return fmt.Errorf("%w: %q: %v", ErrFileOpen, fileheader.Filename, err)
 	}
 	defer file.Close() //nolint:errcheck // not needed
 
@@ -529,25 +533,25 @@
 	}
 
 	if fileheader.Size > 0 && fileheader.Size > int64(maxUploadSize) {
-		return fmt.Errorf("failed to read: %w", fasthttp.ErrBodyTooLarge)
+		return fmt.Errorf("%w: %q: %v", ErrFileRead, fileheader.Filename, fasthttp.ErrBodyTooLarge)
 	}
 
 	buf := bytebufferpool.Get()
 	defer bytebufferpool.Put(buf)
 
 	limitedReader := io.LimitReader(file, int64(maxUploadSize)+1)
 	if _, err = buf.ReadFrom(limitedReader); err != nil {
-		return fmt.Errorf("failed to read: %w", err)
+		return fmt.Errorf("%w: %q: %v", ErrFileRead, fileheader.Filename, err)
 	}
 
 	if buf.Len() > maxUploadSize {
-		return fmt.Errorf("failed to read: %w", fasthttp.ErrBodyTooLarge)
+		return fmt.Errorf("%w: %q: %v", ErrFileRead, fileheader.Filename, fasthttp.ErrBodyTooLarge)
 	}
 
 	data := append([]byte(nil), buf.Bytes()...)
 
 	if err := storage.SetWithContext(c.Context(), path, data, 0); err != nil {
-		return fmt.Errorf("failed to store: %w", err)
+		return fmt.Errorf("%w: %q to %q: %v", ErrFileStore, fileheader.Filename, path, err)
 	}
 
 	return nil

ctx_test.go

@@ -5105,6 +5105,42 @@ func (s *mockContextAwareStorage) Close() error {
 	return nil
 }
 
+func Test_Ctx_SaveFileToStorage_NilFileHeader(t *testing.T) {
+	t.Parallel()
+
+	app := New()
+	storage := memory.New()
+
+	ctx := app.AcquireCtx(&fasthttp.RequestCtx{})
+	defer app.ReleaseCtx(ctx)
+
+	err := ctx.SaveFileToStorage(nil, "test", storage)
+
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrFileHeaderNil)
+}
+
+func Test_Ctx_SaveFileToStorage_ErrorMessageContainsFilename(t *testing.T) {
+	t.Parallel()
+
+	app := New(Config{BodyLimit: 10}) // small limit to force error
+	storage := memory.New()
+
+	ctx := app.AcquireCtx(&fasthttp.RequestCtx{})
+	defer app.ReleaseCtx(ctx)
+
+	fileHeader := createMultipartFileHeader(
+		t,
+		"test-file.png",
+		bytes.Repeat([]byte{'a'}, 100), // bigger than limit
+	)
+
+	err := ctx.SaveFileToStorage(fileHeader, "test-path", storage)
+
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "test-file.png")
+}
+
 // go test -run Test_Ctx_SaveFileToStorage_ContextPropagation
 func Test_Ctx_SaveFileToStorage_ContextPropagation(t *testing.T) {
 	t.Parallel()

error.go

@@ -80,3 +80,11 @@ type (
 	// UnsupportedValueError exposes json.UnsupportedValueError to describe unsupported values encountered during encoding.
 	UnsupportedValueError = json.UnsupportedValueError
 )
+
+// File errors
+var (
+	ErrFileHeaderNil = errors.New("file: file header is nil")
+	ErrFileOpen      = errors.New("file: failed to open file")
+	ErrFileRead      = errors.New("file: failed to read file")
+	ErrFileStore     = errors.New("file: failed to store file")
+)