@@ -50,7 +50,9 @@ let debug = require('internal/util/debuglog').debuglog('quic', (fn) => {
 
 const {
   Endpoint: Endpoint_,
+  sendHeaders,
   setCallbacks,
+  setHeadersInterest,
 
   // The constants to be exposed to end users for various options.
   CC_ALGO_RENO_STR: CC_ALGO_RENO,
@@ -1304,6 +1306,17 @@ function parseHeaderPairs(pairs) {
   return block;
 }
 
+function updateHeaderInterest(handle, inner) {
+  if (handle === undefined) return;
+  setHeadersInterest(
+    handle,
+    inner.onheaders !== undefined ||
+      inner.ontrailers !== undefined ||
+      inner.oninfo !== undefined,
+    inner.onwanttrailers !== undefined || inner.pendingTrailers !== undefined,
+  );
+}
+
 /**
  * Applies session and stream callbacks from an options object to a session.
  * @param {QuicSession} session
@@ -1828,13 +1841,12 @@ class QuicStream {
     const inner = this.#inner;
     if (fn === undefined) {
       inner.onheaders = undefined;
-      inner.state.wantsHeaders = false;
     } else {
       validateFunction(fn, 'onheaders');
       assertHeadersSupported(inner.session);
       inner.onheaders = FunctionPrototypeBind(fn, this);
-      inner.state.wantsHeaders = true;
     }
+    updateHeaderInterest(this.#handle, inner);
   }
 
   /** @type {Function|undefined} */
@@ -1853,6 +1865,7 @@ class QuicStream {
       assertHeadersSupported(inner.session);
       inner.oninfo = FunctionPrototypeBind(fn, this);
     }
+    updateHeaderInterest(this.#handle, inner);
   }
 
   /** @type {Function|undefined} */
@@ -1871,6 +1884,7 @@ class QuicStream {
       assertHeadersSupported(inner.session);
       inner.ontrailers = FunctionPrototypeBind(fn, this);
     }
+    updateHeaderInterest(this.#handle, inner);
   }
 
   /** @type {Function|undefined} */
@@ -1884,13 +1898,12 @@ class QuicStream {
     const inner = this.#inner;
     if (fn === undefined) {
       inner.onwanttrailers = undefined;
-      inner.state.wantsTrailers = false;
     } else {
       validateFunction(fn, 'onwanttrailers');
       assertHeadersSupported(inner.session);
       inner.onwanttrailers = FunctionPrototypeBind(fn, this);
-      inner.state.wantsTrailers = true;
     }
+    updateHeaderInterest(this.#handle, inner);
   }
 
   /**
@@ -1919,10 +1932,12 @@ class QuicStream {
     assertHeadersSupported(inner.session);
     if (headers === undefined) {
       inner.pendingTrailers = undefined;
+      updateHeaderInterest(this.#handle, inner);
       return;
     }
     validateObject(headers, 'headers');
     inner.pendingTrailers = headers;
+    updateHeaderInterest(this.#handle, inner);
   }
 
   /**
@@ -2105,7 +2120,8 @@ class QuicStream {
     const headerString = buildNgHeaderString(
       headers, assertValidPseudoHeader, true /* strictSingleValueFields */);
     const flags = terminal ? kHeadersFlagsTerminal : kHeadersFlagsNone;
-    return this.#handle.sendHeaders(kHeadersKindInitial, headerString, flags);
+    return sendHeaders(
+      this.#handle, kHeadersKindInitial, headerString, flags);
   }
 
   /**
@@ -2124,8 +2140,8 @@ class QuicStream {
     validateObject(headers, 'headers');
     const headerString = buildNgHeaderString(
       headers, assertValidPseudoHeader, true);
-    return this.#handle.sendHeaders(
-      kHeadersKindHints, headerString, kHeadersFlagsNone);
+    return sendHeaders(
+      this.#handle, kHeadersKindHints, headerString, kHeadersFlagsNone);
   }
 
   /**
@@ -2144,8 +2160,8 @@ class QuicStream {
     }
     validateObject(headers, 'headers');
     const headerString = buildNgHeaderString(headers);
-    return this.#handle.sendHeaders(
-      kHeadersKindTrailing, headerString, kHeadersFlagsNone);
+    return sendHeaders(
+      this.#handle, kHeadersKindTrailing, headerString, kHeadersFlagsNone);
   }
 
   /**
@@ -2563,7 +2579,7 @@ class QuicStream {
       assertValidPseudoHeader,
       true, // This could become an option in future
     );
-    return this.#handle.sendHeaders(kind, headerString, flags);
+    return sendHeaders(this.#handle, kind, headerString, flags);
   }
 
   [kFinishClose](error) {
@@ -2671,7 +2687,6 @@ class QuicStream {
 
     switch (kindName) {
       case 'initial':
-        assert(inner.onheaders, 'Unexpected stream headers event');
         inner.headers ??= block;
         if (onStreamHeadersChannel.hasSubscribers) {
           onStreamHeadersChannel.publish({
@@ -2681,7 +2696,8 @@ class QuicStream {
             headers: block,
           });
         }
-        safeCallbackInvoke(inner.onheaders, this, block);
+        if (inner.onheaders)
+          safeCallbackInvoke(inner.onheaders, this, block);
         break;
       case 'trailing':
         if (onStreamTrailersChannel.hasSubscribers) {
@@ -2717,8 +2733,20 @@ class QuicStream {
     // nghttp3 is asking us to provide trailers to send.
     // Check for pre-set pendingTrailers first, then the callback.
     if (inner.pendingTrailers) {
-      this.sendTrailers(inner.pendingTrailers);
+      let sent;
+      try {
+        sent = this.sendTrailers(inner.pendingTrailers);
+      } catch (error) {
+        this.destroy(error);
+        return;
+      }
+      if (!sent) {
+        this.destroy(new ERR_QUIC_STREAM_ABORTED(
+          'Failed to submit trailing headers'));
+        return;
+      }
       inner.pendingTrailers = undefined;
+      updateHeaderInterest(this.#handle, inner);
     } else if (typeof inner.onwanttrailers === 'function') {
       safeCallbackInvoke(inner.onwanttrailers, this);
     }
 
@@ -101,10 +101,8 @@ const {
   IDX_STATE_STREAM_HAS_OUTBOUND,
   IDX_STATE_STREAM_HAS_READER,
   IDX_STATE_STREAM_WANTS_BLOCK,
-  IDX_STATE_STREAM_WANTS_HEADERS,
   IDX_STATE_STREAM_WANTS_RESET,
   IDX_STATE_STREAM_WANTS_STOP_SENDING,
-  IDX_STATE_STREAM_WANTS_TRAILERS,
   IDX_STATE_STREAM_RECEIVED_EARLY_DATA,
   IDX_STATE_STREAM_WRITE_DESIRED_SIZE,
   IDX_STATE_STREAM_BUDGET,
@@ -145,10 +143,8 @@ assert(IDX_STATE_STREAM_RESET !== undefined);
 assert(IDX_STATE_STREAM_HAS_OUTBOUND !== undefined);
 assert(IDX_STATE_STREAM_HAS_READER !== undefined);
 assert(IDX_STATE_STREAM_WANTS_BLOCK !== undefined);
-assert(IDX_STATE_STREAM_WANTS_HEADERS !== undefined);
 assert(IDX_STATE_STREAM_WANTS_RESET !== undefined);
 assert(IDX_STATE_STREAM_WANTS_STOP_SENDING !== undefined);
-assert(IDX_STATE_STREAM_WANTS_TRAILERS !== undefined);
 assert(IDX_STATE_STREAM_WRITE_DESIRED_SIZE !== undefined);
 assert(IDX_STATE_STREAM_RESET_CODE !== undefined);
 
@@ -824,20 +820,6 @@ class QuicStreamState {
     DataViewPrototypeSetUint8(handle, this.#offset + IDX_STATE_STREAM_WANTS_BLOCK, val ? 1 : 0);
   }
 
-  /** @type {boolean} */
-  get wantsHeaders() {
-    const handle = this.#handle;
-    if (handle === undefined) return undefined;
-    return DataViewPrototypeGetUint8(handle, this.#offset + IDX_STATE_STREAM_WANTS_HEADERS) !== 0;
-  }
-
-  /** @type {boolean} */
-  set wantsHeaders(val) {
-    const handle = this.#handle;
-    if (handle === undefined) return;
-    DataViewPrototypeSetUint8(handle, this.#offset + IDX_STATE_STREAM_WANTS_HEADERS, val ? 1 : 0);
-  }
-
   /** @type {boolean} */
   get wantsReset() {
     const handle = this.#handle;
@@ -870,20 +852,6 @@ class QuicStreamState {
       val ? 1 : 0);
   }
 
-  /** @type {boolean} */
-  get wantsTrailers() {
-    const handle = this.#handle;
-    if (handle === undefined) return undefined;
-    return DataViewPrototypeGetUint8(handle, this.#offset + IDX_STATE_STREAM_WANTS_TRAILERS) !== 0;
-  }
-
-  /** @type {boolean} */
-  set wantsTrailers(val) {
-    const handle = this.#handle;
-    if (handle === undefined) return;
-    DataViewPrototypeSetUint8(handle, this.#offset + IDX_STATE_STREAM_WANTS_TRAILERS, val ? 1 : 0);
-  }
-
   /** @type {boolean} */
   get early() {
     const handle = this.#handle;
@@ -948,8 +916,6 @@ class QuicStreamState {
       wantsBlock,
       wantsReset,
       wantsStopSending,
-      wantsHeaders,
-      wantsTrailers,
       early,
       resetCode,
       writeDesiredSize,
@@ -969,8 +935,6 @@ class QuicStreamState {
       wantsBlock,
       wantsReset,
       wantsStopSending,
-      wantsHeaders,
-      wantsTrailers,
       early,
       resetCode: `${resetCode}`,
       writeDesiredSize,
@@ -1007,8 +971,6 @@ class QuicStreamState {
       wantsBlock,
       wantsReset,
       wantsStopSending,
-      wantsHeaders,
-      wantsTrailers,
       early,
       resetCode,
       writeDesiredSize,
@@ -1028,8 +990,6 @@ class QuicStreamState {
       wantsBlock,
       wantsReset,
       wantsStopSending,
-      wantsHeaders,
-      wantsTrailers,
       early,
       resetCode,
       writeDesiredSize,
 
@@ -117,7 +117,7 @@ Maybe<Session::Application_Options> Session::Application_Options::From(
 
   // Ensure the advertised max_field_section_size in SETTINGS is at least
   // as large as max_header_length. Otherwise the peer would be told to
-  // restrict headers to a smaller size than what CanAddHeader accepts.
+  // restrict headers to a smaller size than what the HTTP/3 stream accepts.
   if (options.max_field_section_size < options.max_header_length) {
     options.max_field_section_size = options.max_header_length;
   }
 
@@ -11,6 +11,17 @@
 
 namespace node::quic {
 
+enum class HeadersKind : uint8_t {
+  HINTS,
+  INITIAL,
+  TRAILING,
+};
+
+enum class HeadersFlags : uint8_t {
+  NONE,
+  TERMINAL,
+};
+
 // An Application implements the ALPN-protocol specific semantics on behalf
 // of a QUIC Session.
 class Session::Application : public MemoryRetainer {
@@ -95,13 +106,10 @@ class Session::Application : public MemoryRetainer {
   // Application.
   virtual bool AcknowledgeStreamData(stream_id id, size_t datalen);
 
-  // Called to determine if a Header can be added to this application.
-  // Applications that do not support headers will always return false.
-  virtual bool CanAddHeader(size_t current_count,
-                            size_t current_headers_length,
-                            size_t this_header_length) {
-    return false;
-  }
+  // Called when a pending transport stream receives its stream ID. Protocols
+  // can use this to flush operations that require an opened stream. Returns
+  // false if deferred application data could not be submitted.
+  virtual bool StreamOpened(Stream& stream) { return true; }
 
   // Called when ngtcp2 reports NGTCP2_ERR_STREAM_SHUT_WR for a stream.
   // Applications that manage their own framing (e.g., HTTP/3) must inform
@@ -173,13 +181,19 @@ class Session::Application : public MemoryRetainer {
   // Submits an outbound block of headers for the given stream. Not all
   // Application types will support headers, in which case this function
   // should return false.
-  virtual bool SendHeaders(const Stream& stream,
+  virtual bool SendHeaders(Stream& stream,
                            HeadersKind kind,
                            const v8::Local<v8::Array>& headers,
                            HeadersFlags flags = HeadersFlags::NONE) {
     return false;
   }
 
+  // Updates JavaScript callback interest for an application's stream header
+  // events. Applications without header semantics ignore this.
+  virtual void SetHeadersInterest(Stream& stream,
+                                  bool wants_headers,
+                                  bool wants_trailers) {}
+
   // Returns true if the application protocol supports sending and
   // receiving headers on streams (e.g. HTTP/3). Applications that
   // do not support headers should return false (the default).
Original file line number	Diff line number	Diff line change
`@@ -117,7 +117,7 @@ Maybe<Session::Application_Options> Session::Application_Options::From(`
`117`	`117`
`118`	`118`	`// Ensure the advertised max_field_section_size in SETTINGS is at least`
`119`	`119`	`// as large as max_header_length. Otherwise the peer would be told to`
`120`		`- // restrict headers to a smaller size than what CanAddHeader accepts.`
	`120`	`+ // restrict headers to a smaller size than what the HTTP/3 stream accepts.`
`121`	`121`	`if (options.max_field_section_size < options.max_header_length) {`
`122`	`122`	`options.max_field_section_size = options.max_header_length;`
`123`	`123`	`}`