How do you asynchronously resolve host names to IP addresses?

Question

How do you asynchronously resolve host names to IP addresses, preferably with overlapped I/O? GetAddrInfoEx does not support overlapped I/O in Windows 7 and earlier.

I am using native C++.

Answer 1

For the record, this can be done natively on Windows 7, like this:

• DnsWriteQuestionToBuffer to compose DNS queries yourself for sending.
• DnsExtractRecordsFromMessage to parse DNS responses yourself after receiving.
• WSASendTo in conjunction with WSARecvFrom in a IOCP server for async sending and receiving of DNS queries.

The side effect of this technique is that it's by no means a feat for a novice to easily pull.

Answer 2

libunbound has an asynchronous resolver in it.