fix(render): prevent react hydration markers on large emails (#2383)

Co-authored-by: Gabriel Miranda <gabrielmfern@outlook.com>

.changeset/ninety-lions-train.md

@@ -0,0 +1,5 @@
+---
+"@react-email/render": patch
+---
+
+fix hydration markers on React canary/Next.js latest when rendering large email templates

packages/render/src/browser/render-web.spec.tsx

@@ -146,4 +146,36 @@ describe('render on the browser environment', () => {
     const element = createElement(undefined);
     await expect(render(element)).rejects.toThrowErrorMatchingSnapshot();
   });
+
+  /**
+   * Create a large email that would trigger React's streaming optimization
+   * if progressiveChunkSize wasn't set to Infinity
+   *
+   * @see https://github.com/resend/react-email/issues/2353
+   */
+  it('should render large emails without hydration markers', async () => {
+    const LargeEmailTemplate = () => {
+      const largeContent = Array(100)
+        .fill(null)
+        .map((_, i) => (
+          <p key={i}>
+            This is paragraph {i} with some content to make the email larger.
+            Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do
+            eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
+            ad minim veniam, quis nostrud exercitation ullamco laboris.
+          </p>
+        ));
+
+      return (
+        <div>
+          <h1>Large Email Test</h1>
+          {largeContent}
+        </div>
+      );
+    };
+
+    const actualOutput = await render(<LargeEmailTemplate />);
+
+    expect(actualOutput).toMatchSnapshot();
+  });
 });

packages/render/src/browser/render.tsx

@@ -51,6 +51,7 @@ export const render = async (node: React.ReactNode, options?: Options) => {
         onError(error: unknown) {
           reject(error);
         },
+        progressiveChunkSize: Number.POSITIVE_INFINITY,
       })
       .then(readStream)
       .then(resolve)

packages/render/src/node/render-edge.spec.tsx

@@ -107,4 +107,36 @@ describe('render on the edge', () => {
       `"THIS SHOULD BE RENDERED IN PLAIN TEXT"`,
     );
   });
+
+  /**
+   * Create a large email that would trigger React's streaming optimization
+   * if progressiveChunkSize wasn't set to Infinity
+   *
+   * @see https://github.com/resend/react-email/issues/2353
+   */
+  it('should render large emails without hydration markers', async () => {
+    const LargeEmailTemplate = () => {
+      const largeContent = Array(100)
+        .fill(null)
+        .map((_, i) => (
+          <p key={i}>
+            This is paragraph {i} with some content to make the email larger.
+            Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do
+            eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
+            ad minim veniam, quis nostrud exercitation ullamco laboris.
+          </p>
+        ));
+
+      return (
+        <div>
+          <h1>Large Email Test</h1>
+          {largeContent}
+        </div>
+      );
+    };
+
+    const actualOutput = await render(<LargeEmailTemplate />);
+
+    expect(actualOutput).toMatchSnapshot();
+  });
 });

packages/render/src/node/render-node.spec.tsx

@@ -133,4 +133,36 @@ describe('render on node environments', () => {
       `"THIS SHOULD BE RENDERED IN PLAIN TEXT"`,
     );
   });
+
+  /**
+   * Create a large email that would trigger React's streaming optimization
+   * if progressiveChunkSize wasn't set to Infinity
+   *
+   * @see https://github.com/resend/react-email/issues/2353
+   */
+  it('should render large emails without hydration markers', async () => {
+    const LargeEmailTemplate = () => {
+      const largeContent = Array(100)
+        .fill(null)
+        .map((_, i) => (
+          <p key={i}>
+            This is paragraph {i} with some content to make the email larger.
+            Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do
+            eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
+            ad minim veniam, quis nostrud exercitation ullamco laboris.
+          </p>
+        ));
+
+      return (
+        <div>
+          <h1>Large Email Test</h1>
+          {largeContent}
+        </div>
+      );
+    };
+
+    const actualOutput = await render(<LargeEmailTemplate />);
+
+    expect(actualOutput).toMatchSnapshot();
+  });
 });

packages/render/src/node/render.tsx

@@ -15,7 +15,9 @@ export const render = async (node: React.ReactNode, options?: Options) => {
   let html!: string;
   if (Object.hasOwn(reactDOMServer, 'renderToReadableStream')) {
     html = await readStream(
-      await reactDOMServer.renderToReadableStream(suspendedElement),
+      await reactDOMServer.renderToReadableStream(suspendedElement, {
+        progressiveChunkSize: Number.POSITIVE_INFINITY,
+      }),
     );
   } else {
     await new Promise<void>((resolve, reject) => {
@@ -27,6 +29,7 @@ export const render = async (node: React.ReactNode, options?: Options) => {
         onError(error) {
           reject(error as Error);
         },
+        progressiveChunkSize: Number.POSITIVE_INFINITY,
       });
     });
   }