src: enable StreamPipe for generic StreamBases

Originally landed in the nodejs/quic repo and used there for file
sending.

Original review:

```
  PR-URL: nodejs/quic#150
  Reviewed-By: James M Snell <[email protected]>
```

Author: addaleax

src/stream_pipe.cc

@@ -25,7 +25,7 @@ StreamPipe::StreamPipe(StreamBase* source,
   source->PushStreamListener(&readable_listener_);
   sink->PushStreamListener(&writable_listener_);
 
-  CHECK(sink->HasWantsWrite());
+  uses_wants_write_ = sink->HasWantsWrite();
 
   // Set up links between this object and the source/sink objects.
   // In particular, this makes sure that they are garbage collected as a group,
@@ -66,7 +66,8 @@ void StreamPipe::Unpipe(bool is_in_deletion) {
   is_closed_ = true;
   is_reading_ = false;
   source()->RemoveStreamListener(&readable_listener_);
-  sink()->RemoveStreamListener(&writable_listener_);
+  if (pending_writes_ == 0)
+    sink()->RemoveStreamListener(&writable_listener_);
 
   if (is_in_deletion) return;
 
@@ -126,13 +127,16 @@ void StreamPipe::ReadableListener::OnStreamRead(ssize_t nread,
     // EOF or error; stop reading and pass the error to the previous listener
     // (which might end up in JS).
     pipe->is_eof_ = true;
+    // Cache `sink()` here because the previous listener might do things
+    // that eventually lead to an `Unpipe()` call.
+    StreamBase* sink = pipe->sink();
     stream()->ReadStop();
     CHECK_NOT_NULL(previous_listener_);
     previous_listener_->OnStreamRead(nread, uv_buf_init(nullptr, 0));
     // If we’re not writing, close now. Otherwise, we’ll do that in
     // `OnStreamAfterWrite()`.
-    if (!pipe->is_writing_) {
-      pipe->ShutdownWritable();
+    if (pipe->pending_writes_ == 0) {
+      sink->Shutdown();
       pipe->Unpipe();
     }
     return;
@@ -142,32 +146,40 @@ void StreamPipe::ReadableListener::OnStreamRead(ssize_t nread,
 }
 
 void StreamPipe::ProcessData(size_t nread, AllocatedBuffer&& buf) {
+  CHECK(uses_wants_write_ || pending_writes_ == 0);
   uv_buf_t buffer = uv_buf_init(buf.data(), nread);
   StreamWriteResult res = sink()->Write(&buffer, 1);
+  pending_writes_++;
   if (!res.async) {
     writable_listener_.OnStreamAfterWrite(nullptr, res.err);
   } else {
-    is_writing_ = true;
     is_reading_ = false;
     res.wrap->SetAllocatedStorage(std::move(buf));
     if (source() != nullptr)
       source()->ReadStop();
   }
 }
 
-void StreamPipe::ShutdownWritable() {
-  sink()->Shutdown();
-}
-
 void StreamPipe::WritableListener::OnStreamAfterWrite(WriteWrap* w,
                                                       int status) {
   StreamPipe* pipe = ContainerOf(&StreamPipe::writable_listener_, this);
-  pipe->is_writing_ = false;
+  pipe->pending_writes_--;
+  if (pipe->is_closed_) {
+    if (pipe->pending_writes_ == 0) {
+      Environment* env = pipe->env();
+      HandleScope handle_scope(env->isolate());
+      Context::Scope context_scope(env->context());
+      pipe->MakeCallback(env->oncomplete_string(), 0, nullptr).ToLocalChecked();
+      stream()->RemoveStreamListener(this);
+    }
+    return;
+  }
+
   if (pipe->is_eof_) {
     HandleScope handle_scope(pipe->env()->isolate());
     InternalCallbackScope callback_scope(pipe,
         InternalCallbackScope::kSkipTaskQueues);
-    pipe->ShutdownWritable();
+    pipe->sink()->Shutdown();
     pipe->Unpipe();
     return;
   }
@@ -179,6 +191,10 @@ void StreamPipe::WritableListener::OnStreamAfterWrite(WriteWrap* w,
     prev->OnStreamAfterWrite(w, status);
     return;
   }
+
+  if (!pipe->uses_wants_write_) {
+    OnStreamWantsWrite(65536);
+  }
 }
 
 void StreamPipe::WritableListener::OnStreamAfterShutdown(ShutdownWrap* w,
@@ -202,6 +218,7 @@ void StreamPipe::WritableListener::OnStreamDestroy() {
   StreamPipe* pipe = ContainerOf(&StreamPipe::writable_listener_, this);
   pipe->sink_destroyed_ = true;
   pipe->is_eof_ = true;
+  pipe->pending_writes_ = 0;
   pipe->Unpipe();
 }
 
@@ -242,8 +259,7 @@ void StreamPipe::Start(const FunctionCallbackInfo<Value>& args) {
   StreamPipe* pipe;
   ASSIGN_OR_RETURN_UNWRAP(&pipe, args.Holder());
   pipe->is_closed_ = false;
-  if (pipe->wanted_data_ > 0)
-    pipe->writable_listener_.OnStreamWantsWrite(pipe->wanted_data_);
+  pipe->writable_listener_.OnStreamWantsWrite(65536);
 }
 
 void StreamPipe::Unpipe(const FunctionCallbackInfo<Value>& args) {
@@ -252,6 +268,18 @@ void StreamPipe::Unpipe(const FunctionCallbackInfo<Value>& args) {
   pipe->Unpipe();
 }
 
+void StreamPipe::IsClosed(const FunctionCallbackInfo<Value>& args) {
+  StreamPipe* pipe;
+  ASSIGN_OR_RETURN_UNWRAP(&pipe, args.Holder());
+  args.GetReturnValue().Set(pipe->is_closed_);
+}
+
+void StreamPipe::PendingWrites(const FunctionCallbackInfo<Value>& args) {
+  StreamPipe* pipe;
+  ASSIGN_OR_RETURN_UNWRAP(&pipe, args.Holder());
+  args.GetReturnValue().Set(pipe->pending_writes_);
+}
+
 namespace {
 
 void InitializeStreamPipe(Local<Object> target,
@@ -266,6 +294,8 @@ void InitializeStreamPipe(Local<Object> target,
       FIXED_ONE_BYTE_STRING(env->isolate(), "StreamPipe");
   env->SetProtoMethod(pipe, "unpipe", StreamPipe::Unpipe);
   env->SetProtoMethod(pipe, "start", StreamPipe::Start);
+  env->SetProtoMethod(pipe, "isClosed", StreamPipe::IsClosed);
+  env->SetProtoMethod(pipe, "pendingWrites", StreamPipe::PendingWrites);
   pipe->Inherit(AsyncWrap::GetConstructorTemplate(env));
   pipe->SetClassName(stream_pipe_string);
   pipe->InstanceTemplate()->SetInternalFieldCount(1);

src/stream_pipe.h

@@ -17,6 +17,8 @@ class StreamPipe : public AsyncWrap {
   static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Start(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Unpipe(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void IsClosed(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void PendingWrites(const v8::FunctionCallbackInfo<v8::Value>& args);
 
   SET_NO_MEMORY_INFO()
   SET_MEMORY_INFO_NAME(StreamPipe)
@@ -26,14 +28,13 @@ class StreamPipe : public AsyncWrap {
   inline StreamBase* source();
   inline StreamBase* sink();
 
-  inline void ShutdownWritable();
-
+  int pending_writes_ = 0;
   bool is_reading_ = false;
-  bool is_writing_ = false;
   bool is_eof_ = false;
   bool is_closed_ = true;
   bool sink_destroyed_ = false;
   bool source_destroyed_ = false;
+  bool uses_wants_write_ = false;
 
   // Set a default value so that when we’re coming from Start(), we know
   // that we don’t want to read just yet.