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Ask HN: How do you check a url is valid?
So it is trivial to check a url is valid using regex, but if you wanted to take this one step further and make sure it is a valid domain name that is registered and actually in use...how would you do this? I have a few ideas for how to achieve this with a Microservice but I feel like others may have solved this problem before and there may be better solutions out there.
- ultrablue 9y agocurllib will tell you whether there's something there, presuming the network is available. In fact, a simple HEAD request will suffice for that. That would also prove that the domain is registered, presuming DNS is working.
- icebraining 9y agoThat's not enough; some registrars keep a domain parked and responding after the registration has expired.
- lookingfj 9y agoAnd this is exactly the problem I want to solve and the key challenge
- icebraining 9y agoCheck Whois, DNS and make an HTTP request? This feels like an XY Problem, though. What are you trying to achieve by checking if the URL is valid?
- lookingfj 9y agoThat the url is valid
- pwg 9y agoFirst, you need to be precise in what you mean by "valid". "Valid" can encompass at least these four possibilities: 1) the url follows the correct syntax for url's; 2) the url is valid as per #1 and further the "host" portion of the url (when it contains a name) can be resolved to an IP address; 3) the url is valid as per #2 and further there is a server located at the host (and optional port) value encoded in the URL that responds to requests; 4) The url is valid as per #3 and further the path and/or query and fragment parts defines a valid path on the server running at the host:port encoded in the url. #1 you can do yourself, as it is just a check that the syntax is correct. All of numbers 2-4 require some form of 'lookup' occur from some other system in order to verify 'validity'.
- lookingfj 9y agoSo I think in this instance I would deem valid to be: 1) the url is the correct format 2) the url resolves to an ip address 3) the url is registered and is in use. By this I mean it's not one of the "this domain name is for sale" pages. Number 3 is the novel and challenging piece of this.