问题
To PROGRAMMATICALLY verify if a domain exists I do the following:
- DNS Query it and see if it resolves. If it does, it's obviously registered. So no need for step 2. If it doesn't, it might STILL be registered. So a whois check is required.
- Backtrack from
whois.iana.organd see if the designated whois server knows the domain or not.
Well, whois is not really meant for bulk checking. Not to mention that the RFC has only 4 pages and there's no clear specifications as to the format or even the encoding of the data. So you pretty much have to train the parser for each specific answer format (server).
Is there a way to circumvent the whois query and check (as close to the metal as possible) if the domain is registered in another (publicly available) standardized (preferably free or affordable) way? And not by downloading the TLD zone file or using third-party APIs (as they have a bad habit of snatching domains that you check before you get to register them). :)
I know registrars have their own protocol but I'm not sure if it's open to public use.
回答1:
There isn't really any good way to do this accurately without looking at zone files or checking directly with the registry, unfortunately.
Registrars typically use a protocol like EPP to talk to a registry, check name availability and place orders. It's unlikely that anyone other than an accredited registrar would be permitted to use this protocol, but it may be worth checking with the registry that manages the TLDs you are interested in, e.g. Verisign.
I'd (personally) be wary of relying too much on DNS queries or WHOIS lookups to ascertain whether a particular domain exists, as both can produce inaccurate results from time to time. For example, certain TLDs have name servers configured for any unregistered domain name (they often direct you to the registry's website). The Vietnamese registry is one example of this. WHOIS lookups can fail for any number of reasons, so lack of a record is not concrete evidence of the domain's availability.
来源：https://stackoverflow.com/questions/27331478/check-if-domain-is-registered-or-not-without-whois