Play the YouTube embed with a referrer instead of in an iframe

Peter, on the previous build: "the inline player now plays the audio but
the video is a black screen." So Error 153 is gone and the stream is
decoding -- what is left is a display problem.

The iframe was not needed in the first place. A `Referer` header alone
satisfies the embed, which means the player can be the WebView's own
ordinary top-level document again. That drops two constructs the last
build added: a `loadDataWithBaseURL` page, whose origin is synthetic,
and a cross-origin subframe inside it. Both have a history of rendering
video oddly in WebView, and the black screen appeared with them.

Measured on an Android user agent -- no referrer: Error 153; `&origin=`
in the query: Error 153; inside an iframe: plays; with a `Referer`
header: plays. The referrer is a constant on a reserved `.invalid`
domain rather than the article's URL, so YouTube learns which app asked
and nothing about what is being read -- the same reason the nocookie
domain is used.

Confirmed in the app's own WebView: the embed loads with no error,
854x480, readyState 4, playing.

NOT confirmed: that a picture now reaches the screen. This emulator
cannot render video in a WebView at all -- it hard-crashed the AVD
twice, including on a plain <video> in an ordinary non-dialog WebView --
so the one thing that matters here can only be checked on real
hardware.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

1 files changed, 18 insertions, 27 deletions

diff --git a/app/src/test/java/org/terst/feedreader/ui/YouTubeLinksTest.kt b/app/src/test/java/org/terst/feedreader/ui/YouTubeLinksTest.kt
index 3afba16..af9884d 100644
--- a/app/src/test/java/org/terst/feedreader/ui/YouTubeLinksTest.kt
+++ b/app/src/test/java/org/terst/feedreader/ui/YouTubeLinksTest.kt
@@ -90,46 +90,37 @@ class YouTubeLinksTest {
         assertNull(youTubeTargetForLongPress("not a url at all"))
     }
 
-    // --- the embed page ------------------------------------------------------------------
+    // --- the embed ----------------------------------------------------------------------
 
     @Test
-    fun `the embed page puts the player in an iframe, which is the whole point`() {
-        val html = youTubeEmbedPageHtml("dQw4w9WgXcQ")
+    fun `the embed url is the privacy-preserving nocookie one, playing inline`() {
+        val url = youTubeEmbedUrl("dQw4w9WgXcQ")
 
-        assertTrue("loading the embed top-level is what YouTube rejects: $html", html.contains("<iframe"))
-        assertTrue(html.contains("https://www.youtube-nocookie.com/embed/dQw4w9WgXcQ"))
+        assertTrue(url.startsWith("https://www.youtube-nocookie.com/embed/dQw4w9WgXcQ"))
+        assertTrue(url.contains("autoplay=1"))
+        assertTrue(url.contains("playsinline=1"))
     }
 
     @Test
-    fun `the embed page keeps autoplay and inline playback`() {
-        val html = youTubeEmbedPageHtml("dQw4w9WgXcQ")
-
-        assertTrue(html.contains("autoplay=1"))
-        assertTrue(html.contains("playsinline=1"))
-        assertTrue("without this the iframe is not allowed to autoplay", html.contains("allow=\"autoplay"))
+    fun `the embed is sent a referrer, which is the whole reason it plays`() {
+        assertTrue(YOUTUBE_EMBED_REFERRER.startsWith("https://"))
     }
 
     @Test
-    fun `the base URL is a real https origin, since that is what the embed requires`() {
-        assertTrue(YOUTUBE_EMBED_BASE_URL.startsWith("https://"))
-    }
-
-    @Test
-    fun `the base URL is not YouTube's own origin`() {
-        assertFalse(
-            "the embed has to be a guest on somebody else's page, not its own",
-            YOUTUBE_EMBED_BASE_URL.contains("youtube")
-        )
+    fun `the referrer says nothing about what is being read`() {
+        // A constant, so YouTube learns the app and nothing else. The article's own URL would
+        // work just as well and would tell YouTube what he reads, which is the thing the
+        // nocookie domain is already chosen to avoid.
+        assertFalse(YOUTUBE_EMBED_REFERRER.contains("?"))
+        assertTrue("a reserved TLD can never become somebody's real site", YOUTUBE_EMBED_REFERRER.contains(".invalid"))
     }
 
     @Test
-    fun `a video id that could break out of the attribute is scrubbed`() {
-        val html = youTubeEmbedPageHtml("""a"><script>alert(1)</script>""")
+    fun `a video id that could break out of the url is scrubbed`() {
+        val url = youTubeEmbedUrl("""a"><script>alert(1)</script>""")
 
-        assertFalse("markup from the id reached the page: $html", html.contains("<script"))
-        assertFalse(html.contains("alert(1)"))
-        // What is left is only ever id characters, so the src attribute still closes where it should.
-        assertTrue(html.contains("embed/ascriptalert1script?"))
+        assertFalse("markup from the id reached the url: $url", url.contains("<"))
+        assertTrue(url.startsWith("https://www.youtube-nocookie.com/embed/ascriptalert1script?"))
     }
 
     @Test