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Webmaster Forum / HTML, CSS, Scripts / JavaScript / April 2007javascript dns look up
hi, Has anyone come across a "hack" to do a dns look up via JS I want to evaluate an email address against a server to see if it is valid , I'm 50 % of the way there but i need a way to look up the email servers MX record. I just wondered if there was a way to trigger a dns spew on port 53 Steve > hi, > Has anyone come across a "hack" to do a dns look up via JS If you are using IE, you could use activex winsock control. If not, you would need to submit the page back to the server to do it...  Signature.~. Might, Courage, Vision, SINCERITY. http://www.linux-sxs.org / v \ Simplicity is Beauty! May the Force and Farce be with you! /( _ )\ (Ubuntu 6.10) Linux 2.6.21.1 ^ ^ 19:18:01 up 4:11 0 users load average: 1.00 1.00 1.00 news://news.3home.net news://news.hkpcug.org news://news.newsgroup.com.hk >> hi, >> Has anyone come across a "hack" to do a dns look up via JS > > If you are using IE, you could use activex winsock control. If not, you > would need to submit the page back to the server to do it... it has to be cross platform, if it was as easy as being able to use activex I would be laughing. Yes i can submit it back to the server, but I wanted the mental challenge. steve > >> Has anyone come across a "hack" to do a dns look up via JS > [quoted text clipped - 4 lines] > I would be laughing. > Yes i can submit it back to the server, but I wanted the mental challenge. Javascript does not have socket capabilities, so out of Javascript itself it is plain impossible. Write a few-liners server-side script on Perl, invoke it using GET/ iframe, script implant, ajaxoid or remote service. If server-side script gets HELLO from the remote daemon, let it send text/plain "var emai_ok=true;" otherwise let it send back "var email_ok=false;" Then just use the return value in your client-side script for check. Obviously email_ok variable can be called any way you like. There is no mental challenge in this trivia - simply take care of timeout fallbacks - some SMTP servers are deadly slow. > hi, > Has anyone come across a "hack" to do a dns look up via JS [quoted text clipped - 6 lines] > > Steve imagine the best case scenario where you have a javascript which can talk the right protocols and send and receive data from a DNS server, will port 53 be open on the client. The best way is therefore to have your webserver perform the check based on the value of somepost, and send back the result via XHR or an iframe, however, I'm not sure that MX records actually /have/ to exist (I read it along time ago) although the A record does, and so provided there is at least an A record you are ok. cacert.org uses pretty good email testing suite you could purloin, by downloading their source code, which is open (despite some copyright notices still hanging around) their script tests the server with a connection attempt without actually sending them mail. (dont forget to ban all those temporary domains - btw if you have or find a maintained list of temporary email domians, could you post a link here) :) > > hi, > > Has anyone come across a "hack" to do a dns look up via JS [quoted text clipped - 10 lines] > talk the right protocols and send and receive data from a DNS server, > will port 53 be open on the client. i shoudl have said "can the client get to port 53 on an external server" they might be forced to use a proxy on a LAN, or a socks etc... The best way is therefore to have > your webserver perform the check based on the value of somepost, and > send back the result via XHR or an iframe, however, I'm not sure that [quoted text clipped - 7 lines] > you have or find a maintained list of temporary email domians, could > you post a link here) :) >>> hi, >>> Has anyone come across a "hack" to do a dns look up via JS [quoted text clipped - 28 lines] >> you have or find a maintained list of temporary email domians, could >> you post a link here) :) Hi Shimmy, sorry I do not have any pointers to temp email domain list, I imagine it changes every day steve . > Has anyone come across a "hack" to do a dns look up via JS > I want to evaluate an email address against a server to see if it is valid , > I'm 50 % of the way there but i need a way to look up the email servers MX > record. You may be wasting your time. Many ISPs reject all outbound SMTP traffic, except to their own outgoing mailserver. So you won't be able to establish an SMTP dialog directly with the target user's mailserver. Also, most mailservers no longer support the SMTP VRFY command - or they seem to support it, but actually lie (eg. they say that *all* addresses are valid). Your only remaining possibility is to check the response to a dummy RCPT TO command - but I'm not sure that even this is reliable now. Try picking a relevant user's mailserver (not your ISP's outgoing mailserver), and use Telnet to test the process manually. For example: telnet mail.blah.com 25 HELO me VRFY someuser MAIL FROM me RCPT TO someuser (or somesuch) If you cann't get it to work via Telnet, you won't be able to program it - in Javascript or anything else. HTH, TC (MVP MSAccess) http://tc2.atspace.com > > Has anyone come across a "hack" to do a dns look up via JS > > I want to evaluate an email address against a server to see if it is valid , [quoted text clipped - 28 lines] > HTH, > TC (MVP MSAccess)http://tc2.atspace.com the smtp traffic would be server side of course, the results sent back via javascript. > > > Has anyone come across a "hack" to do a dns look up via JS > > > I want to evaluate an email address against a server to see if it is valid , [quoted text clipped - 30 lines] > > the smtp traffic would be server side of course, the results sent back via javascript Understood. I assumed, probably incorrectly, that the code would run on a client PC. But none-the-less, I still think he will not be able to do what he wants (for other reasons stated above). Cheers, TC (MVP MSAccess) http://tc2.atspace.com |
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