fix: preserve files only on client

packages/conform-dom/formdata.ts

@@ -165,22 +165,28 @@ export function isFile(obj: unknown): obj is File {
  * Normalize value by removing empty object or array, empty string and null values
  */
 export function normalize<Type extends Record<string, unknown>>(
-	value: Type | null,
-): Type | null | undefined;
+	value: Type,
+	acceptFile?: boolean,
+): Type | undefined;
 export function normalize<Type extends Array<unknown>>(
-	value: Type | null,
-): Type | null | undefined;
-export function normalize(value: unknown): unknown | undefined;
+	value: Type,
+	acceptFile?: boolean,
+): Type | undefined;
+export function normalize(
+	value: unknown,
+	acceptFile?: boolean,
+): unknown | undefined;
 export function normalize<
 	Type extends Record<string, unknown> | Array<unknown>,
 >(
-	value: Type | null,
-): Record<string, unknown> | Array<unknown> | null | undefined {
+	value: Type,
+	acceptFile = true,
+): Record<string, unknown> | Array<unknown> | undefined {
 	if (isPlainObject(value)) {
 		const obj = Object.keys(value)
 			.sort()
 			.reduce<Record<string, unknown>>((result, key) => {
-				const data = normalize(value[key]);
+				const data = normalize(value[key], acceptFile);
 
 				if (typeof data !== 'undefined') {
 					result[key] = data;
@@ -201,26 +207,17 @@ export function normalize<
 			return undefined;
 		}
 
-		return value.map(normalize);
+		return value.map((item) => normalize(item, acceptFile));
 	}
 
 	if (
 		(typeof value === 'string' && value === '') ||
 		value === null ||
-		(isFile(value) && value.size === 0)
+		(isFile(value) && (!acceptFile || value.size === 0))
 	) {
 		return;
 	}
 
-	// We will skip serializing file if the result is sent to the client
-	if (isFile(value)) {
-		return Object.assign(value, {
-			toJSON() {
-				return;
-			},
-		});
-	}
-
 	return value;
 }
 

packages/conform-dom/submission.ts

@@ -278,7 +278,12 @@ export function replySubmission<FormError>(
 	return {
 		status: context.intent ? undefined : error ? 'error' : 'success',
 		intent: context.intent ? context.intent : undefined,
-		initialValue: normalize(context.payload) ?? {},
+		initialValue:
+			normalize(
+				context.payload,
+				// We can't serialize the file and send it back from the server, but we can preserve it in the client
+				typeof document !== 'undefined',
+			) ?? {},
 		error,
 		state: context.state,
 		fields: Array.from(context.fields),

playground/app/routes/metadata.tsx

@@ -27,8 +27,33 @@ const schema = z.object({
 				bookmarks.length,
 			'Bookmark URLs are repeated',
 		),
+	file: z.instanceof(File, { message: 'File is required' }),
+	files: z
+		.instanceof(File)
+		.array()
+		.min(1, 'At least 1 file is required')
+		.refine(
+			(files) => files.every((file) => file.type === 'application/json'),
+			'Only JSON file is accepted',
+		),
 });
 
+const getPrintableValue = (value: unknown) => {
+	if (typeof value === 'undefined') {
+		return;
+	}
+
+	return JSON.parse(
+		JSON.stringify(value, (key, value) => {
+			if (value instanceof File) {
+				return `${value.name} (${value.size} bytes)`;
+			}
+
+			return value;
+		}),
+	);
+};
+
 export async function loader({ request }: LoaderArgs) {
 	const url = new URL(request.url);
 
@@ -62,14 +87,14 @@ export default function Example() {
 	const bookmarks = fields.bookmarks.getFieldList();
 
 	return (
-		<Form method="post" {...getFormProps(form)}>
+		<Form method="post" {...getFormProps(form)} encType="multipart/form-data">
 			<Playground
 				title="Metadata"
 				result={{
 					form: {
 						status: form.status,
 						initialValue: form.initialValue,
-						value: form.value,
+						value: getPrintableValue(form.value),
 						dirty: form.dirty,
 						valid: form.valid,
 						errors: form.errors,
@@ -107,6 +132,22 @@ export default function Example() {
 						errors: bookmarks[1]?.errors,
 						allErrors: bookmarks[1]?.allErrors,
 					},
+					file: {
+						initialValue: fields.file.initialValue,
+						value: getPrintableValue(fields.file.value),
+						dirty: fields.file.dirty,
+						valid: fields.file.valid,
+						errors: fields.file.errors,
+						allErrors: fields.file.allErrors,
+					},
+					files: {
+						initialValue: fields.files.initialValue,
+						value: getPrintableValue(fields.files.value),
+						dirty: fields.files.dirty,
+						valid: fields.files.valid,
+						errors: fields.files.errors,
+						allErrors: fields.files.allErrors,
+					},
 				}}
 			>
 				<Field label="Title" meta={fields.title}>
@@ -128,6 +169,12 @@ export default function Example() {
 						</fieldset>
 					);
 				})}
+				<Field label="File" meta={fields.file}>
+					<input {...getInputProps(fields.file, { type: 'file' })} />
+				</Field>
+				<Field label="Files" meta={fields.files}>
+					<input {...getInputProps(fields.files, { type: 'file' })} multiple />
+				</Field>
 			</Playground>
 		</Form>
 	);