The underlying sink has been closed; writing is no longer possible.
The stream’s .close() method has been called, and a command to close is in the queue or being processed by the underlying sink; attempts to write will now fail.
An error occurred interacting with the underlying sink or the stream has been aborted, so the stream is now dead.
The stream’s internal queue is full; that is, the stream is exerting backpressure.
The stream’s internal queue is not full; call .write() until backpressure is exerted.