Set the request body of a [class@Message].
If content_type is null and stream is not null
the Content-Type header will not be changed if present. The request body needs to be set again in case
this is restarted (in case of redirection or authentication).
| this |
the message |
| content_type |
MIME Content-Type of the body, or null if unknown |
| stream |
a InputStream to read the request body from |
| content_length |
the byte length of |