Bear in mind that there will be an issue if the contents is read and then,
for whatever reason, the auto-restart is triggered.

If :content-length is set, and :content is a stream, only copy
that many bytes, otherwise, set transfer-encoding to chunked, and copy
the entirety of the stream.

If :content is a stream and :content-length is a specified header,
set :content-length and copy that many bytes.

If :content is a stream and :content-length is not specified,
set :transfer-encoding to chunked, and copy the entire stream.

The :content-type in both cases is defaulted to "application/octet-stream"