I did this

I am using the curl multi interface with boost::asio, which cannot wait on sockets without taking ownership of them. For most sockets this is fine, since curl will create them via the CURLOPT_OPENSOCKETFUNCTION callback and close them with the CURLOPT_CLOSESOCKETFUNCTION callback, so asio can open and close them on its own. However, c-ares does not use those functions and instead opens and closes the sockets itself. This means that when curl passes the c-ares socket to the CURLMOPT_SOCKETFUNCTION it isn't owned by asio, and asio can't take ownership of the socket because c-ares will later close the socket. This means the program can't wait on data from that socket and so can't call curl_multi_socket_action at the right time.

I expected the following

Curl should use the OPEN/CLOSESOCKETFUNCTION to open/close c-ares sockets.

curl/libcurl version

curl 7.61.0-DEV (x86_64-pc-linux-gnu) libcurl/7.61.0-DEV OpenSSL/1.1.0h zlib/1.2.11 brotli/1.0.5 c-ares/1.14.0 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) nghttp2/1.32.0
Release-Date: [unreleased]
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp smb smbs smtp smtps telnet tftp
Features: AsynchDNS IDN IPv6 Largefile NTLM NTLM_WB SSL libz brotli TLS-SRP HTTP2 UnixSockets HTTPS-proxy PSL

operating system

Linux, Windows