[Fizz] Fallback to client replaying actions if we're trying to serialize a Blob

packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js

@@ -1019,12 +1019,7 @@ function pushAdditionalFormField(
 ): void {
   const target: Array<Chunk | PrecomputedChunk> = this;
   target.push(startHiddenInputChunk);
-  if (typeof value !== 'string') {
-    throw new Error(
-      'File/Blob fields are not yet supported in progressive forms. ' +
-        'It probably means you are closing over binary data or FormData in a Server Action.',
-    );
-  }
+  validateAdditionalFormField(value, key);
   pushStringAttribute(target, 'name', key);
   pushStringAttribute(target, 'value', value);
   target.push(endOfStartTagSelfClosing);
@@ -1040,6 +1035,23 @@ function pushAdditionalFormFields(
   }
 }
 
+function validateAdditionalFormField(value: string | File, key: string): void {
+  if (typeof value !== 'string') {
+    throw new Error(
+      'File/Blob fields are not yet supported in progressive forms. ' +
+        'Will fallback to client hydration.',
+    );
+  }
+}
+
+function validateAdditionalFormFields(formData: void | null | FormData) {
+  if (formData != null) {
+    // $FlowFixMe[prop-missing]: FormData has forEach.
+    formData.forEach(validateAdditionalFormField);
+  }
+  return formData;
+}
+
 function getCustomFormFields(
   resumableState: ResumableState,
   formAction: any,
@@ -1048,7 +1060,11 @@ function getCustomFormFields(
   if (typeof customAction === 'function') {
     const prefix = makeFormFieldPrefix(resumableState);
     try {
-      return formAction.$$FORM_ACTION(prefix);
+      const customFields = formAction.$$FORM_ACTION(prefix);
+      if (customFields) {
+        validateAdditionalFormFields(customFields.data);
+      }
+      return customFields;
     } catch (x) {
       if (typeof x === 'object' && x !== null && typeof x.then === 'function') {
         // Rethrow suspense.

packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMForm-test.js

@@ -17,6 +17,23 @@ global.ReadableStream =
 global.TextEncoder = require('util').TextEncoder;
 global.TextDecoder = require('util').TextDecoder;
 
+// Polyfill stream methods on JSDOM.
+global.Blob.prototype.stream = function () {
+  const impl = Object.getOwnPropertySymbols(this)[0];
+  const buffer = this[impl]._buffer;
+  return new ReadableStream({
+    start(c) {
+      c.enqueue(new Uint8Array(buffer));
+      c.close();
+    },
+  });
+};
+
+global.Blob.prototype.text = async function () {
+  const impl = Object.getOwnPropertySymbols(this)[0];
+  return this[impl]._buffer.toString('utf8');
+};
+
 // Don't wait before processing work on the server.
 // TODO: we can replace this with FlightServer.act().
 global.setTimeout = cb => cb();
@@ -962,4 +979,80 @@ describe('ReactFlightDOMForm', () => {
     expect(form2.textContent).toBe('error message');
     expect(form2.firstChild.tagName).toBe('DIV');
   });
+
+  // @gate enableAsyncActions && enableBinaryFlight
+  it('useActionState can return binary state during MPA form submission', async () => {
+    const serverAction = serverExports(
+      async function action(prevState, formData) {
+        return new Blob([new Uint8Array([104, 105])]);
+      },
+    );
+
+    let blob;
+
+    function Form({action}) {
+      const [errorMsg, dispatch] = useActionState(action, null);
+      let text;
+      if (errorMsg) {
+        blob = errorMsg;
+        text = React.use(blob.text());
+      }
+      return <form action={dispatch}>{text}</form>;
+    }
+
+    const FormRef = await clientExports(Form);
+
+    const rscStream = ReactServerDOMServer.renderToReadableStream(
+      <FormRef action={serverAction} />,
+      webpackMap,
+    );
+    const response = ReactServerDOMClient.createFromReadableStream(rscStream, {
+      ssrManifest: {
+        moduleMap: null,
+        moduleLoading: null,
+      },
+    });
+    const ssrStream = await ReactDOMServer.renderToReadableStream(response);
+    await readIntoContainer(ssrStream);
+
+    const form1 = container.getElementsByTagName('form')[0];
+    expect(form1.textContent).toBe('');
+
+    async function submitTheForm() {
+      const form = container.getElementsByTagName('form')[0];
+      const {formState} = await submit(form);
+
+      // Simulate an MPA form submission by resetting the container and
+      // rendering again.
+      container.innerHTML = '';
+
+      const postbackRscStream = ReactServerDOMServer.renderToReadableStream(
+        {formState, root: <FormRef action={serverAction} />},
+        webpackMap,
+      );
+      const postbackResponse =
+        await ReactServerDOMClient.createFromReadableStream(postbackRscStream, {
+          ssrManifest: {
+            moduleMap: null,
+            moduleLoading: null,
+          },
+        });
+      const postbackSsrStream = await ReactDOMServer.renderToReadableStream(
+        postbackResponse.root,
+        {formState: postbackResponse.formState},
+      );
+      await readIntoContainer(postbackSsrStream);
+    }
+
+    await expect(submitTheForm).toErrorDev(
+      'Warning: Failed to serialize an action for progressive enhancement:\n' +
+        'Error: File/Blob fields are not yet supported in progressive forms. Will fallback to client hydration.',
+    );
+
+    expect(blob instanceof Blob).toBe(true);
+    expect(blob.size).toBe(2);
+
+    const form2 = container.getElementsByTagName('form')[0];
+    expect(form2.textContent).toBe('hi');
+  });
 });

scripts/error-codes/codes.json

@@ -465,7 +465,7 @@
   "477": "React Internal Error: processHintChunk is not implemented for Native-Relay. The fact that this method was called means there is a bug in React.",
   "478": "Thenable should have already resolved. This is a bug in React.",
   "479": "Cannot update optimistic state while rendering.",
-  "480": "File/Blob fields are not yet supported in progressive forms. It probably means you are closing over binary data or FormData in a Server Action.",
+  "480": "File/Blob fields are not yet supported in progressive forms. Will fallback to client hydration.",
   "481": "Tried to encode a Server Action from a different instance than the encoder is from. This is a bug in React.",
   "482": "async/await is not yet supported in Client Components, only Server Components. This error is often caused by accidentally adding `'use client'` to a module that was originally written for the server.",
   "483": "Hooks are not supported inside an async component. This error is often caused by accidentally adding `'use client'` to a module that was originally written for the server.",