Fix transitions with non-recommended headers (#9464)

* Reproduce edge case in test

* Fix edge case

* Add changeset

* Update .changeset/khaki-ducks-give.md

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

---------

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

.changeset/khaki-ducks-give.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an edge case with view transitions where some spec-compliant `Content-Type` headers would cause a valid HTML response to be ignored.

packages/astro/e2e/fixtures/view-transitions/src/pages/one.astro

@@ -6,6 +6,7 @@ import Layout from '../components/Layout.astro';
 	<a id="click-one" href="#test">test</a>
 	<a id="click-two" href="/two">go to 2</a>
 	<a id="click-three" href="/three">go to 3</a>
+	<a id="click-seven" href="/seven">go to 7</a>
 	<a id="click-longpage" href="/long-page">go to long page</a>
 	<a id="click-self" href="">go to top</a>
 	<a id="click-redirect-two" href="/redirect-two">go to redirect 2</a>

packages/astro/e2e/fixtures/view-transitions/src/pages/seven.astro

@@ -0,0 +1,10 @@
+---
+import Layout from '../components/Layout.astro';
+
+Astro.response.headers.set('Content-Type', 'text/html ; charset=utf-8');
+---
+<Layout link="/one.css">
+	<p id="seven">Page 7</p>
+
+	<div id="test">test content</div>
+</Layout>

packages/astro/e2e/view-transitions.test.js

@@ -97,6 +97,25 @@ test.describe('View Transitions', () => {
 		expect(loads.length, 'There should only be 1 page load').toEqual(1);
 	});
 
+	test('Clicking on a link to a page with non-recommended headers', async ({page, astro}) => {
+		const loads = [];
+		page.addListener('load', (p) => {
+			loads.push(p.title());
+		});
+
+		// Go to page 4
+		await page.goto(astro.resolveUrl('/one'));
+		let p = page.locator('#one');
+		await expect(p, 'should have content').toHaveText('Page 1');
+
+		// Go to page 1
+		await page.click('#click-seven');
+		p = page.locator('#seven');
+		await expect(p, 'should have content').toHaveText('Page 7');
+
+		expect(loads.length, 'There should only be 1 page load').toEqual(1);
+	});
+
 	test('Moving to a page without ViewTransitions triggers a full page navigation', async ({
 		page,
 		astro,

packages/astro/src/transitions/router.ts

@@ -119,8 +119,9 @@ async function fetchHTML(
 ): Promise<null | { html: string; redirected?: string; mediaType: DOMParserSupportedType }> {
 	try {
 		const res = await fetch(href, init);
+		const contentType = res.headers.get('content-type') ?? '';
 		// drop potential charset (+ other name/value pairs) as parser needs the mediaType
-		const mediaType = res.headers.get('content-type')?.replace(/;.*$/, '');
+		const mediaType = contentType.split(';', 1)[0].trim();
 		// the DOMParser can handle two types of HTML
 		if (mediaType !== 'text/html' && mediaType !== 'application/xhtml+xml') {
 			// everything else (e.g. audio/mp3) will be handled by the browser but not by us