Asynchronously sends msg and waits for the beginning of a response.
When callback is called, then either msg has been sent, and its response headers received, or else an error has
occurred. Call [[email protected]_finish] to get a [[email protected]] for reading the response body.
See [[email protected]] for more details on the general semantics.
| this |
a Session |
| msg |
a Message |
| io_priority |
the I/O priority of the request |
| cancellable |
a Cancellable |
| callback |
the callback to invoke |
| user_data |
data for |