fix: correctly handle data URL with hashes.

lib/fetch/dataURL.js

@@ -125,11 +125,12 @@ function URLSerializer (url, excludeFragment = false) {
     return href
   }
 
-  const hash = href.lastIndexOf('#')
-  if (hash === -1) {
-    return href
-  }
-  return href.slice(0, hash)
+  // Note: Since there are at least two characters in the url,
+  // the scheme and the U+003A (:) character,
+  // the hash searches after these.
+  const hash = href.indexOf('#', 2)
+
+  return hash === -1 ? href : href.substring(0, hash)
 }
 
 // https://infra.spec.whatwg.org/#collect-a-sequence-of-code-points

test/fetch/data-uri.js

@@ -191,3 +191,17 @@ test('https://domain.com/?', (t) => {
   const serialized = URLSerializer(new URL(domain))
   t.equal(serialized, domain)
 })
+
+// https://github.com/nodejs/undici/issues/2474
+test('data url that includes the hash', async (t) => {
+  t.plan(2)
+  const dataURL = 'data:,node#js#'
+  const serialized = URLSerializer(new URL(dataURL), true)
+  t.equal('data:,node', serialized)
+  try {
+    const res = await fetch(dataURL)
+    t.equal(await res.text(), 'node')
+  } catch (error) {
+    t.fail(`failed to fetch ${dataURL}`)
+  }
+})