http2: store headersSent after stream destroyed

Store headersSent directly on response state after finish event
is triggered, so that users can always access it.

PR-URL: #15232
Fixes: #15226
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

lib/internal/http2/compat.js

@@ -320,7 +320,7 @@ class Http2ServerResponse extends Stream {
 
   get headersSent() {
     const stream = this[kStream];
-    return stream.headersSent;
+    return stream !== undefined ? stream.headersSent : this[kState].headersSent;
   }
 
   get sendDate() {
@@ -542,6 +542,7 @@ class Http2ServerResponse extends Stream {
     if (code !== undefined)
       state.closedCode = code;
     state.closed = true;
+    state.headersSent = this[kStream].headersSent;
     this.end();
     this[kStream] = undefined;
     this.emit('finish');

test/parallel/test-http2-compat-serverresponse-headers.js

@@ -88,6 +88,7 @@ server.listen(0, common.mustCall(function() {
 
     response.on('finish', common.mustCall(function() {
       assert.strictEqual(response.code, h2.constants.NGHTTP2_NO_ERROR);
+      assert.strictEqual(response.headersSent, true);
       server.close();
     }));
     response.end();