The following form retrieves a plain text document via FTP,
effectively using a URL of the form
where number is the user input.
The technique used combines the efficiency of client-side scripting
with the reliability of server-side scripting.
There is also a simpler example which
reads a URL as user input and redirects the browser to that URL.
Oh well, in this particular case the server-side scripting is not that reliable. Please do not assume that the redirection scripts at the particular URLs will stay available. In real-life situations, you'd like to use something that you have control over. This is just a demonstration of a concept!
The basic strategy is the following:
formtag has an
formtag has an
actionattribute referring to a server-side script which sends a redirect to the browser (if part 1, client-side scripting, does not work).
Here's the form:
You could now change your browser settings, disabling or
enabling client-side scripting and reloading the page.
Watch what happens
(though this might fail due to deficiencies in the
implementation of the
<form action="http://www.cs.tut.fi/cgi-bin/run/~jkorpela/ftpget.cgi" name="rfcform" onSubmit= "location.href='ftp://ftp.funet.fi/pub/doc/rfc/rfc' + document.rfcform.number.value + '.txt';return false"> <input type=submit value="Get RFC #"> <input type=hidden name=server value="ftp.funet.fi"> <input type=hidden name=pathstart value="pub/doc/rfc/rfc"> <input type=hidden name=pathend value=".txt"> <input type=text name=number size=4 maxlength=4> </form>
The server-side script at address
is written in
very short (the first line is system-dependent):
#!/usr/local/gnu/bin/perl use CGI qw(:standard); print "Location: ftp://",param('server'),'/',param('pathstart'), param('number'),param('pathend'),"\n\n";
Thus, the server-side script simply sends back
via HTTP (see RFC 2068).
The browser will then use the URL included in it as if
the user had followed a link with that specific URL.
To illustrate the basic idea better, this document uses a very simple technique and does not check the user input. So if you type nonnumeric input, you'll get a more or less cryptic error message.
For related information, see
How about writing a construct which lets the user type a URL and sends the browser to that URL? It's unclear to me why people ask how to do that; are users expected to be idiots who can't learn to type the URL directly to the browser? My guess is that authors who have this problem have themselves created it by making (or trying to make) a page open in a browser window without the usual tools; cf. to my notes on popup windows.
Well, if we don't consider error checking, the technique
is actually even simpler, since we expect to have a full URL already
(you might help the user by prefilling
people tend to omit it).
<form action="http://www.cs.tut.fi/cgi-bin/run/~jkorpela/redirect.cgi" name="getform" onsubmit= "location.href=document.getform.url.value;return false"> Please type a URL: <input type="text" name="url" size="40"value="http://"> <input type="submit" value="Go"> </form>
Here's the script at
#!/usr/local/gnu/bin/perl use CGI qw(:standard); print "Location: ", param('url'),
And here's a demo;
Date of last update: 2001-08-27