What's the fastest way to check if an URL exists?
I tried:
if URL "http://www.whatever.com/something/else.html"; is empty then blah blah blah end if
Very very slow. Is there a faster way?
You'll get different results, depending on whether the host server (www.whatever.com) or the resource on the server (/something/else.html) doesn't exist. If it's the latter, then typically you'll get a 404 response (the result will return "error 404" plus a descriptive string, often "file not found") But data is usually returned from such a url call, consisting of the "missing page html message" that http servers usually return. So checking for empty won't work in this case. However, the whole process shouldn't be slow.
The "missing host" shouldn't be slow either if the DNS lookup returns quickly. (libUrl does a lookup with hostNameToAdress before making any requests.) "invalid host address" is returned in the result.
A delay is most likely to occur because of connection problems, or when using numerical IP addresses (192.168.1.1, etc.) that don't exist on the local network.
At 2:33 am -0500 7/11/03, Brian Yennie wrote:
I think the only way that will be technically faster than this would be to use sockets, and make a HEAD request, rather than a GET for the url in question.
You'd have to look up http protocol, but basically what it does it let you get just the http headers for a page rather than the contents. You'd also have to parse the return code...
In theory, it should be possible to make a HEAD request using the libUrlSetCustomHttpHeaders routine. But I just checked, and it's flawed. libUrl tries to read for data beyond the returned headers, and you have to wait for a timeout before it returns. I'll try and fix this in a future revision, probably with a specific routine for using HEAD. Meawhile, here's a *quickly* concocted routine for sending HEAD requests. (WARNING: it really needs socketError and socketTimeout handlers and a way to jump out of the waits in the main routine if something goes wrong.)
## this in a button somewhere ## substitue your values for tHost, tResource, tPort on mouseUp
put "www.whatever.com" into tHost
put "80" into tPort
put "/something/else.html" into tResource
put empty into tData
doHEAD tHost, tPort, tResource, tData
if the result <> empty then
answer the result
else
answer tData
end if
end mouseUp------------------------------------ ## this part in the message path (card, stack, library) local lvWritten, lvReadData, lvReaded
on doHEAD pHost, pPort, pResource, @pResponse
put "HEAD" && pResource && "HTTP/1.1" into tHeaders put crlf & "Host:" && pHost after tHeaders put crlf & "User-Agent: Metacard" after tHeaders ##optional put crlf & crlf after tHeaders
put pHost & ":" & pPort into tSocket open socket to tSocket if the result is not empty then return the result
put empty into lvWritten
write tHeaders to socket tSocket with message "written"
if the result <> empty then
put the result into tRes
close socket tSocket
return tRes
end ifwait until lvWritten <> empty with messages
put empty into lvReaded
read from socket tSocket with message "readed"
if the result <> empty then
put the result into tRes
close socket tSocket
return tRes
end ifwait until lvReaded <> empty with messages put lvReadData into pResponse close socket tSocket return empty
end doHEAD
on written x, y put true into lvWritten end written
on readed x,y put y into lvReadData put true into lvReaded end readed -----------------------------------
Cheers Dave _______________________________________________ metacard mailing list [EMAIL PROTECTED] http://lists.runrev.com/mailman/listinfo/metacard
