We are using QNetworkAccessManager to set up the GET request and use the returned QNetworkReply to read the data stream. This works fine.
We tried to send extra information over this open connection by using the QNetworkReply::write method, but this fails as QNetworkReply is read-only.
(We know that this is probably an HTTP limitation, but our application requires to do so.)

Does anybody have an idea on how to send data over the open connection?

(Context: We are building an Ntrip client. Communication to the server happens over HTTP. The server replies to the GET request with an ongoing stream of data. In Ntrip, the client can (repeatedly) send during this ongoing communication extra information to the server in order to finetune the data to be replied.)