Re: Sending a different protocol header
--- Geoffrey Young [EMAIL PROTECTED] wrote: btw, can you please explain what ICY is for me? I believe ICY is a protocol used for streaming media, so these headers are probably an extension of HTTP that can be used instead of the pure ICY protocol. That's a guess, anyway. :-) Chris = Become a better Web developer with the HTTP Developer's Handbook http://httphandbook.org/
Re: The best place for mod_perl beginners to get started.
--- Geoffrey Young [EMAIL PROTECTED] wrote: and don't forget about the cookbook http://www.modperlcookbook.org/ Speaking of that, why is it missing from http://perl.apache.org/? Chris
RE: use http-equiv to refresh the page
I just wanted to mention that the meta tag as well as its http-equiv attribute are both official parts of the HTML standard and have been for quite some time. Yes and no. Well, I disagree with the no. I will explain it again below. HTML 4.0 has a section on META and http-requiv. In it, it mentions that \Some user agents support the use of META to refresh the current page after a specified number of seconds, with the option of replacing it by a different URI.\ and proceeds with an example. That sounds more advisory than part of the standard. But for the sake of argument, let\'s say it\'s part of the standard, and check what HTML 4.01 has to say. HTML 4.01 also has a section on META and http-requiv. However, the only reference to \refresh\ is: \Note. Some user agents support the use of META to refresh the current page after a specified number of seconds, with the option of replacing it by a different URI. Authors should __not__ use this technique to forward users to different pages, as this makes the page inaccessible to some users. Instead, automatic page forwarding should be done using server-side redirects.\ I\'m guessing this is because http-equiv is designed to hold an HTTP header, but there is no such thing as an \Refresh\ header in HTTP. No, there is an HTTP header called Refresh, and it is standard. The meta tag and the http-equiv attribute of the meta tag are also standard. However, some people seem to be confusing HTTP and HTML here for some reason. Refresh is an HTTP standard, while the meta tag is HTML. The http-equiv attribute of the meta tag allows some HTTP headers to be specified in the HTML. While this feature offers little to mod_perl developers who can manipulate the headers themselves anyway, it was historically very helpful to developers for providing accurate HTTP headers such as Expires when they could not otherwise do this. The reason for that warning in the HTML specification is due to what the W3C likely considers a rampant abuse of the Refresh header which was not intended for redirection but only for refreshing the current resource. They are not warning against Refresh alone but rather what they consider a misuse of Refresh. The key phrase is, \with the option of replacing it by a different URI.\ This is what is frowned upon, not the meta HTML tag nor the Refresh HTTP header. So http-equiv=\refresh\ is no longer standard. Of course, this is all theoretical. In practice, too many people are not easily swayed by a measily thing such as a standard. Right, and this was my second point in an earlier message. Support for this rogue feature is pretty widespread, though it should not be completely trusted. As one of the other posters pointed out, there are Web clients that do not support the use of a meta tag for redirection, but many (possibly most) do. It is quite common to see the use of a meta tag for redirection accompanied by instructions on the screen and a link for users that are not automatically redirected. By accomodating the users who are not automatically redirected, you can eliminate the possibility of a dead-end. Of course, I hope that mod_perl developers always choose manipulating the real HTTP headers over the use of the http-equiv attribute of the meta tag. Also, it seems possible that there might be much wider support for redirection with the real Refresh HTTP header than for the meta tag equivalent. I know of at least one attempt to test and document support for this specific use: http://www.hixie.ch/tests/evil/mixed/refresh1.http.html Perhaps the results of this test can help a developer determine whether this misuse of the Refresh header is appropriate for a certain situation. Chris
Re: use http-equiv to refresh the page
Is using meta tag a \bad\ approach? Yes. It\'s something that Netscape added to their browser, which others may or may not add to their browsers. It\'s not part of any HTTP spec and isn\'t guaranteed to work, even on totally correct web browsers. A meta tag is not something unique to Netscape nor the least bit uncommon. It is supported by all major Web browsers and has been for quite some time. While its use may be discouraged over a protocol-level redirect at times, it is appropriate for some situations and appears to be appropriate for what the original poster is trying to accomplish. As with any other HTML tag, the meta tag does not need to be part of an HTTP specification in order to be valid. Also, it is guaranteed to work on any compliant Web browser. HTML has its own specification, and the latest version describes the meta tag here: http://www.w3.org/TR/html4/struct/global.html#h-7.4.4.2 Sorry for disagreeing like this, but I am always afraid to see people being given incorrect information that might cause them difficulty. I hope this helps clarify. Chris
Re: use http-equiv to refresh the page
Perrin Harkins wrote: Chris Shiflett wrote: http://www.w3.org/TR/html4/struct/global.html#h-7.4.4.2 Look a little further down that page: /*Note.* Some user agents support the use of META http://www.w3.org/TR/html4/struct/global.html#edef-META to refresh the current page after a specified number of seconds, with the option of replacing it by a different URI. Authors should *not* use this technique to forward users to different pages, as this makes the page inaccessible to some users. Instead, automatic page forwarding should be done using server-side redirects./ I might be overzealous about this, but I dislike seeing HTTP-EQUIV meta tags used when actual HTTP headers are available to do the same thing. It's fine if there's a reason for it, but usually people do it because they don't realize they can just send a real header instead.. No, I actually agree with you completely on that last bit and am of the opinion that using the http-equiv attribute is a leftover habit from the early days of Web development when manipulating HTTP headers was not as convenient as it is now. I just wanted to mention that the meta tag as well as its http-equiv attribute are both official parts of the HTML standard and have been for quite some time. Netscape also introduced things like cookies and SSL, but that should in no way discredit the technology. The W3C's stance on refresh is the same for the header as well as the meta tag: they did not originally intend for it to be used to specify a *different* URL as a rudimentary method of redirection. They meant it to be used to refresh the current resource only. However, this rogue practice of redirection is quite common with both the header and the meta tag and is very well supported by browsers. In fact, I am not aware of any Web client that supports refresh but also limits the URL to the current resource only. It is also the only option for the pause, then redirect behavior the original poster desired that I can think of. Chris
Re: redirection halts if a message is printed
Sumitro Chowdhury wrote:
Case I ( simple redirection ):
--
package redirect.pm
use Apache::Const -compile =
qw(HTTP_MOVED_TEMPORARILY);
sub handler (
my $r = shift;
$r-content_type('text/html');
$r-headers_out-{'Location'}=
http://new.location;;
return HTTP_MOVED_TEMPORARILY;
}
1;
Result is : browser immediately loads the new page.
Case II ( Print a message before redirection )
--
package redirect.pm
use Apache::Const -compile =
qw(HTTP_MOVED_TEMPORARILY);
sub handler (
my $r = shift;
$r-content_type('text/html');
print Redirecting to new site ...;
$r-headers_out-{'Location'}=
http://new.location;;
return HTTP_MOVED_TEMPORARILY;
}
1;
Result is : Instead of opening the new URL, the
following is displayed on the browser :
Redirecting to new site ...
Ok
The document has moved here (here is clickable).
...
My question is :
a)What is the reason for this behaviour ? Why does
printing a message halt the redirection ?
b)What needs to be done to display a message saying
Redirecting .. and then the browser to auto-display
the new URL ?
a. When your script outputs something (sending a message as you say),
you are telling Apache that you are finished sending the HTTP headers
and have begun the content part of the response. Thus, it is too late
for the Location header you later want to send. This is a protocol
restriction based on the construction of an HTTP message. To avoid this,
you have to either send all of your HTTP headers first (my preference),
or you need to buffer your output until you are finished sending your
headers.
b. It sounds like you are wanting the user to visit an intermediate page
displaying a Redirecting ... message before being forwarded to a final
destination. In this case, you probably want to use HTTP's Refresh
header or the HTML equivalent: meta http-equiv=refresh value=???.
Both have the same syntax:
3; url=http://example.org/
In this example, the 3 is the number of seconds you want the client to
wait prior to sending the next request, which will be for the URL
http://example.org/.
Chris
