v0.29.3

src/proxy/error_fallback.rs

@@ -8,6 +8,11 @@ struct InternalFallbackRoute {
 #[derive(Clone)]
 struct FinalRouteContext(crate::config::CompiledRoute);
 
+/// The named location has already produced the terminal HTTP response.
+/// In particular, do not replace its 404 HTML with a global/vhost error page.
+#[derive(Clone, Copy)]
+struct ErrorFallbackResponse;
+
 #[derive(Clone)]
 struct ErrorFallbackRequest {
     method: Method,
@@ -88,6 +93,21 @@ async fn prepare_error_fallback_body(request: &mut Request, enabled: bool) -> Re
         return Ok(ErrorFallbackBody::Replayable(Bytes::new()));
     }
     let Some(length) = request.body().size_hint().exact() else {
+        // HTTP/2 and HTTP/3 frequently expose an *empty* GET/HEAD body as a
+        // stream with no exact size hint. Refusing to inspect that stream
+        // silently disables the configured 404 fallback. Only peek for safe
+        // bodyless methods; an actual payload is replayed back into the
+        // original request and is never discarded or forwarded twice.
+        if request.method() == Method::GET || request.method() == Method::HEAD {
+            return match empty_for_cache(request).await {
+                Ok(true) => Ok(ErrorFallbackBody::Replayable(Bytes::new())),
+                Ok(false) => Ok(ErrorFallbackBody::Unavailable),
+                Err(_) => Err(error(
+                    StatusCode::BAD_REQUEST,
+                    "RustProxy: invalid or incomplete request body\n",
+                )),
+            };
+        }
         return Ok(ErrorFallbackBody::Unavailable);
     };
     if length > MAX_ERROR_FALLBACK_REPLAY_BODY_BYTES {
@@ -131,6 +151,13 @@ async fn execute_error_fallback(
         .select_internal_on(host, &frontend.id, &fallback.target, local.0, tls)
         .cloned()
     else {
+        tracing::warn!(
+            vhost = %frontend.id,
+            route = %route.id,
+            target = %fallback.target,
+            status = status.as_u16(),
+            "error fallback target could not be resolved on this frontend"
+        );
         return None;
     };
     let ErrorFallbackBody::Replayable(body) = body else {
@@ -148,6 +175,7 @@ async fn execute_error_fallback(
         },
     );
     let mut response = Box::pin(forward_request(state, peer, local, request)).await;
+    response.extensions_mut().insert(ErrorFallbackResponse);
     if response.extensions().get::<FinalRouteContext>().is_none() {
         response.extensions_mut().insert(FinalRouteContext(target));
     }