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How do I know when to execute a UTF8 or punycode DNS query?

I have an application with an address bar, and users enter an IRI that I have to connect to.

On unix / Darwin, it's simple: I am smoothing IDNs to URIs as described in RFC3987. That is, if the circuit has a privilege section, I map this to ASCII with punycode, and then encode the percentages of any non-ASCII characters in the rest of the IRI.

There are two possibilities in Windows: either the domain name is a regular Internet resource, in which case it must be mapped to ASCII with punycode and look for a normal DNS. Or the domain name is a strange Windows server (for example, an Active Directory DNS server), and the search should be UTF-8.

Examples

  • User types http://☃.net : call getaddrinfo(service="xn--n3h.net") .
  • User types http://dryden.internal.corp.com : calling getaddrinfo(service="dryden.internal.corp.com") will work getaddrinfo(service="dryden.internal.corp.com") fine.
  • User types http://pöp.internal.corp.com :
    • calling getaddrinfo(service="xn--pp-fka.internal.corp.com") does not work if "pöp" is the machine name published by DNS UTF-8.
    • a call to GetAddrInfoW(service=T"pöp.internal.corp.com") works.

Firefox and Chrome simultaneously run directly on any IRI, so they cannot resolve strange Microsoft domains.

Rules?

What guidelines exist for processing IRI in such an environment? Are there any recommended ways to guess which kind of DNS lookup should be performed, punycode or UTF-8 DNS? What do other apps do?

My best attempt at a solution is to first punycode if it is a public TLD, but skip the punycode attempt if TLD is internal (acme.com can serve public things, acme.ltd is probably an intranet). If punycode failed or was skipped, I try to execute a UTF-8 request.

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There is one workaround with a negative impact on response time - if all else fails, you can try to make 2 calls using both methods and get an answer from the first to succeed.

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Source: https://habr.com/ru/post/1483588/

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