- fold DoH and async HTTPS-RR handling into common code.
have common cleanups, etc. Have a CURLcode result in async
handling to allow HTTPS RR parsing to fail.
- keep target, ipv4hints, ipv6hints, port and echconfig also
when resolving via cares. We need to know `target` and `port`
when evaluating possible ALPN candidates to not go astray.
- add CURL_TRC_DNS for tracing DNS operations
- replace DoH specific tracing with DNS, use doh as alias
for dns in curl_global_tracea()
Closes#16132
Allow building with c-ares and yet use threaded resolver for the main
host A/AAAA resolving:
`--with-ares` provides the c-ares install path and defaults to use
c-ares for name resolving
`--with-threaded-resolver` still uses c-ares in the build (for HTTPS)
but uses the threaded resolver for "normal" resolves.
It works similarly for cmake: ENABLE_ARES enables ares, and if
ENABLE_THREADED_RESOLVER also is set, c-ares is used for HTTPS RR and
the threaded resolver for "normal" resolves.
HTTPSRR and c-ares-rr are new features return by curl_version_info() and
thus shown by curl -V.
The c-ares-rr feature bit is there to make it possible to distinguish
between builds using c-ares for all name resolves and builds that use
the threaded resolves for the regular name resolves and c-ares for
HTTPSRR only. "c-ares-rr" means it does not use c-ares for "plain" name
resolves.
HTTPSRR support is EXPERIMENTAL only.
Closes#16054
