ensure proxy urls have a host in front and not simple "/" path

src/providers/mod.rs

@@ -671,6 +671,22 @@ pub fn build_proxy_url(options: &ServerOptions, proxy: &str, target: &str) -> St
     }
 }
 
+/// Re-applies the public host to a (possibly host-relative) proxy URL.
+///
+/// Provider results are cached as fully-rendered items, so the `public_url_base`
+/// in effect when an item is *first* built gets baked into its proxy URLs. Items
+/// first produced by runtime validation (which has no request, so
+/// `public_url_base` is `None`) therefore carry host-relative `/proxy/...` URLs.
+/// Response handlers call this with the host derived from the incoming request so
+/// every proxy URL is absolute, regardless of which context populated the cache.
+pub fn ensure_proxy_url_host(url: &str, public_url_base: &str) -> String {
+    let base = public_url_base.trim_end_matches('/');
+    if base.is_empty() || !url.starts_with("/proxy/") {
+        return url.to_string();
+    }
+    format!("{base}{url}")
+}
+
 fn channel_metadata_for(id: &str) -> Option<ProviderChannelMetadata> {
     include!(concat!(env!("OUT_DIR"), "/provider_metadata_fn.rs"))
 }
@@ -1678,4 +1694,36 @@ mod tests {
             eprintln!("skipped providers:\n{}", skipped.join("\n"));
         }
     }
+
+    #[test]
+    fn ensure_proxy_url_host_prepends_host_to_relative_proxy_urls() {
+        // Host-relative proxy URL (as produced when public_url_base was None,
+        // e.g. by runtime validation) gets the request host applied.
+        assert_eq!(
+            ensure_proxy_url_host("/proxy/sxyprn/post/abc", "http://hottub:18080"),
+            "http://hottub:18080/proxy/sxyprn/post/abc"
+        );
+        // A trailing slash on the base is not duplicated.
+        assert_eq!(
+            ensure_proxy_url_host("/proxy/sxyprn/post/abc", "http://hottub:18080/"),
+            "http://hottub:18080/proxy/sxyprn/post/abc"
+        );
+        // Already-absolute URLs are left untouched.
+        assert_eq!(
+            ensure_proxy_url_host("https://cdn.example/v.mp4", "http://hottub:18080"),
+            "https://cdn.example/v.mp4"
+        );
+        assert_eq!(
+            ensure_proxy_url_host(
+                "http://other:18080/proxy/sxyprn/post/abc",
+                "http://hottub:18080"
+            ),
+            "http://other:18080/proxy/sxyprn/post/abc"
+        );
+        // Empty base leaves the URL as-is rather than producing a bare host.
+        assert_eq!(
+            ensure_proxy_url_host("/proxy/sxyprn/post/abc", ""),
+            "/proxy/sxyprn/post/abc"
+        );
+    }
 }