http2: no stream destroy while its data is on the wire

This fixes a crash that occurred when a `Http2Stream` write
is completed after it is already destroyed.

Instead, don’t destroy the stream in that case and wait for
GC to take over.

Fixes: nodejs#18973

src/node_http2.cc

@@ -1700,6 +1700,13 @@ void Http2Session::OnStreamRead(ssize_t nread, const uv_buf_t& buf) {
   stream_buf_ = uv_buf_init(nullptr, 0);
 }
 
+bool Http2Session::HasWritesOnSocketForStream(Http2Stream* stream) {
+  for (const nghttp2_stream_write& wr : outgoing_buffers_)
+    if (wr.req_wrap != nullptr && wr.req_wrap->stream() == stream)
+      return true;
+  return false;
+}
+
 // Every Http2Session session is tightly bound to a single i/o StreamBase
 // (typically a net.Socket or tls.TLSSocket). The lifecycle of the two is
 // tightly coupled with all data transfer between the two happening at the
@@ -1753,13 +1760,11 @@ Http2Stream::Http2Stream(
 
 
 Http2Stream::~Http2Stream() {
+  DEBUG_HTTP2STREAM(this, "tearing down stream");
   if (session_ != nullptr) {
     session_->RemoveStream(this);
     session_ = nullptr;
   }
-
-  if (!object().IsEmpty())
-    ClearWrap(object());
 }
 
 // Notify the Http2Stream that a new block of HEADERS is being processed.
@@ -1837,15 +1842,19 @@ inline void Http2Stream::Destroy() {
     Http2Stream* stream = static_cast<Http2Stream*>(data);
     // Free any remaining outgoing data chunks here. This should be done
     // here because it's possible for destroy to have been called while
-    // we still have qeueued outbound writes.
+    // we still have queued outbound writes.
     while (!stream->queue_.empty()) {
       nghttp2_stream_write& head = stream->queue_.front();
       if (head.req_wrap != nullptr)
         head.req_wrap->Done(UV_ECANCELED);
       stream->queue_.pop();
     }
 
-    delete stream;
+    // We can destroy the stream now if there are no writes for it
+    // already on the socket. Otherwise, we'll wait for the garbage collector
+    // to take care of cleaning up.
+    if (!stream->session()->HasWritesOnSocketForStream(stream))
+      delete stream;
   }, this, this->object());
 
   statistics_.end_time = uv_hrtime();

src/node_http2.h

@@ -878,6 +878,9 @@ class Http2Session : public AsyncWrap, public StreamListener {
   // Removes a stream instance from this session
   inline void RemoveStream(Http2Stream* stream);
 
+  // Indicates whether there currently exist outgoing buffers for this stream.
+  bool HasWritesOnSocketForStream(Http2Stream* stream);
+
   // Write data to the session
   inline ssize_t Write(const uv_buf_t* bufs, size_t nbufs);
 

test/parallel/test-http2-write-finishes-after-stream-destroy.js

@@ -0,0 +1,62 @@
+// Flags: --expose-gc
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const assert = require('assert');
+const http2 = require('http2');
+const makeDuplexPair = require('../common/duplexpair');
+
+// Make sure the Http2Stream destructor works, since we don't clean the
+// stream up like we would otherwise do.
+process.on('exit', global.gc);
+
+{
+  const { clientSide, serverSide } = makeDuplexPair();
+
+  let serverSideHttp2Stream;
+  let serverSideHttp2StreamDestroyed = false;
+  const server = http2.createServer();
+  server.on('stream', common.mustCall((stream, headers) => {
+    serverSideHttp2Stream = stream;
+    stream.respond({
+      'content-type': 'text/html',
+      ':status': 200
+    });
+
+    const originalWrite = serverSide._write;
+    serverSide._write = (buf, enc, cb) => {
+      if (serverSideHttp2StreamDestroyed) {
+        serverSide.destroy();
+        serverSide.write = () => {};
+      } else {
+        setImmediate(() => {
+          originalWrite.call(serverSide, buf, enc, () => setImmediate(cb));
+        });
+      }
+    };
+
+    // Enough data to fit into a single *session* window,
+    // not enough data to fit into a single *stream* window.
+    stream.write(Buffer.alloc(40000));
+  }));
+
+  server.emit('connection', serverSide);
+
+  const client = http2.connect('http://localhost:80', {
+    createConnection: common.mustCall(() => clientSide)
+  });
+
+  const req = client.request({ ':path': '/' });
+
+  req.on('response', common.mustCall((headers) => {
+    assert.strictEqual(headers[':status'], 200);
+  }));
+
+  req.on('data', common.mustCallAtLeast(() => {
+    if (!serverSideHttp2StreamDestroyed) {
+      serverSideHttp2Stream.destroy();
+      serverSideHttp2StreamDestroyed = true;
+    }
+  }));
+}