Adds a "meta_hash" to each easy handle for keeping special data during
operations. All meta data set needs to add its destructor callback, so
that meta data gets destroyed properly when the easy handle is cleaned
up or reset.
Add data->master_mid for "sub" transfers that belong to a "master" easy
handle. When a "sub" transfer is done, the corresponding "master" can
add a callback to be invoked. Used in DoH name resolution.
DoH: use easy meta hash to add internal structs for DoH name resolution.
One in each in each probe easy handle. When probes are done, response
data is copied from the probe to the initiating easy.
This allows DoH using transfers and their probes to be cleaned up in any
sequence correctly.
Fold DoH cleanup into the Curl_async_shutdown() and Curl_async_destroy()
functions.
Closes#16384
"asyn" is the internal name under which both c-ares and threaded
resolver operate. Make the naming more consistent. Implement the c-ares
resolver in `asyn-ares.*` and the threaded resolver in `asyn-thrdd.*`.
The common functions are in `asyn-base.c`.
When `CURLRES_ASYNCH` is defined, either of the two is used and
`data->state.async` exists. Members of that struct vary for the selected
implementation, but have the fields `hostname`, `port` and `ip_version`
always present. This are populated when the async resolving starts and
eliminate the need to pass them again when checking on the status and
processing the results of the resolving.
Add a `Curl_resolv_blocking()` to `hostip.h` that relieves FTP and SOCKS
from having to repeat the same code.
`Curl_resolv_check()` remains the function to check for status of
ongoing resolving. Now it also performs internally the check if the
needed DNS entry exists in the dnscache and if so, aborts the asnyc
operation. (libcurl right now does not check for duplicate resolve
attempts. an area for future improvements).
The number of functions in `asyn.h` has been reduced. There were subtle
difference in "cancel()" and "kill()" calls, both replaced by
`Curl_async_shutdown()` now. This changes behaviour for threaded
resolver insofar as the resolving thread is now always joined unless
`data->set.quick_exit` is set. Before this was only done on some code
paths. A future improvement would be a thread pool that keeps a limit
and also could handle joins more gracefully.
DoH, not previously tagged under "asny", has its struct `doh_probes` now
also in `data->state.async`, moved there from `data->req` because it
makes more sense. Further integration of DoH underneath the "asyn"
umbrella seems like a good idea.
Closes#16963
