PHP手册 - Get and/or set the current cache limiter

**Possible values**
Value	Headers sent
public	Expires: (sometime in the future, according session.cache_expire) Cache-Control: public, max-age=(sometime in the future, according to session.cache_expire) Last-Modified: (the timestamp of when the session was last saved)
private_no_expire	Cache-Control: private, max-age=(session.cache_expire in the future), pre-check=(session.cache_expire in the future) Last-Modified: (the timestamp of when the session was last saved)
private	Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: private, max-age=(session.cache_expire in the future), pre-check=(session.cache_expire in the future) Last-Modified: (the timestamp of when the session was last saved)
nocache	Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache

版本	说明
4.2.0	The private_no_expire cache limiter was added.

PHP手册 - N: Get and/or set the current cache limiter

用户评论:

Marina (05-Apr-2011 04:01)

There is one scenario when you want to go in and change the default 'nocache' setting to something else - usually 'public': when serving flash files over a secured SSL connection. While most browsers handle things just fine with default settings, IE of any version seems to refuse to load Flash unless this setting is something *other* than 'nocache'. Set it to 'public', restart apache - works like a charm.

Tomas Liubinas (14-Mar-2010 10:24)

FALSE parameter disables any automatic cache limiter In this case no additional headers are sent <?php session_cache_limiter( FALSE ); ?>

ire dot ogunsina at gmail dot com (01-Oct-2008 03:55)

I have had some trouble preventing IE, particular IE 7 to stop caching pages. I read quite a number of articles relating to people's experiences and how they fixed it but it was hard to find one that worked for me. Eventually I had to use the following fix: <META HTTP-EQUIV="Pragma" CONTENT="no-cache"> <META HTTP-EQUIV="Expires" CONTENT="-1"> based on the information available on following url: http://support.microsoft.com/kb/234067 Would to God that we'd all quit IE for good. Hope this saves someone some agony over IE.

yves at kochira point com (08-Sep-2008 09:58)

To avoid a headache while trying the various parameters in Firefox 3.0.1 (+Firebug), just restart the browser after a change... or they're not taken into account (from 'no-cache' to 'public'/'private').

scott at realorganized dot com (02-May-2008 07:03)

http://us.php.net/session_cache_limiter sends: Pragma: no-cache under some conditions from server to client. Internet Explorer has a strange interpretation of: Pragma: No-cache being sent from the server to the client. Here's the link: http://support.microsoft.com/kb/234067 If the client communicates with the server over a secure connection (https://) and the server returns a Pragma: no-cache header with the response, Internet Explorer does not cache the response. Note, however, that the Pragma: no-cache header was not intended for this. According to the HTTP 1.0 and 1.1 specifications, this header is defined in the context of a request only, not a response, and is actually intended for proxy servers that may prevent certain important requests from reaching the destination Web server. For future applications, the Cache-Control header is the proper means for controlling caching. For this reason, watch out when using the Pragma: no-cache with https and IE

clay at killersoft dot com (30-Mar-2008 01:44)

The actual headers that are set using the values described above are: public: Expires: pageload + 3 hours Cache-Control: public, max-age=10800 private: Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: private, max-age=10800, pre-check=10800 nocache: Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache private_no_expire: Cache-Control: private, max-age=10800, pre-check=10800 Regarding other settings mentioned by some, those just don't do anything. Check the source of PHP, in ext/session/session.c -- the above values are all that actually do anything. Other values, or an emtpy string, result in no cache-limiting headers being set at all.

david at ordal dot com (25-Mar-2008 10:28)

We did quite a lot of trial and error testing in IE 6/7 and FireFox 2.X to see what magic combo worked so that 1) the browser would cache the state of the page, but 2) The browser or intermediate proxies wouldn't cache the entire page. Thus a NEW request would reload the page, but back/forward browser navigation wouldn't force a reload. We found this worked best across browsers: session_cache_limiter ('private_no_expire, must-revalidate');

brinley at etcorp dot com (31-Aug-2007 04:30)

For those people trying to fix IE6's problem of recognizing the filename attribute in Content-Disposition. I thought I'd add that in addition to the fixes mentioned before, you have to take note of invalid and sensitive characters in the file name. For example, having a space or colon in the filename will cause IE6 to use a randomly generated filename.

Typer85 at gmail dot com (13-Jul-2007 10:16)

Here is another handy trick for your session lovers out there; It seems that using 'nocache' as an argument for this function, will prevent users browsing your website using IE 6 from viewing your HTML source file! Probable reason ... probably because IE 6 is not caching anything due to the headers it is receiving, see my post below this one, and since IE 6 by default loads HTML source files from its cache, it can not find a file to open using notepad, since no file will exist in the cache! I am not sure if this is the same with IE 7, but Mozilla Firefox does not have this problem. Thank you Microsoft for yet another 'quality' product ( I read that somewhere and thought it was funny) ... at least now someone has a pretty neat trick up there hand to hide away their HTML source. Do not know who ... but you are out there I am sure :)

Typer85 at gmail dot com (13-Jul-2007 09:19)

Here is some magic for you PHP session lovers out there; it seems that if you use 'nocache' as an argument for this function, PHP will send the following headers automatically for you: -------------- Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache -------------- Which pretty much render any cache ineffective because no proxy or browser that follows the HTTP 1.1 protocol will cache your request. In short, every page request, whether explicitly through a page reload or not, will go through your server. Not something good for those of us looking for a bit of security but also for some performance juice. The only way to override these headers, if you use the 'nocache' as an argument, is to use the header( ) function after you start your session but before you send any output: <?php // Above Headers Sent By PHP. session_cache_limiter( 'nocache' ); // Start Session. session_start( ); // Override Headers. header( 'Cache-Control: no-cache, must-revalidate, post-check=3600, pre-check=3600' ); ?>

Fernando Gabrieli fgabrieli at gmail (07-Apr-2007 01:21)

<? session_cache_limiter ('private, must-revalidate'); $cache_limiter = session_cache_limiter(); // session_cache_expire(60); // in minutes session_start() ; ?> If i do not set must-revalidate, IE seems to cache session variables without refreshing them If i post a form then it refreshes the variables Firefox does not have this problem So, be sure to use must-revalidate

Jeremiah at jkjonesco dot com (30-Oct-2006 11:20)

If you are trying to work with dynamic binaries such as videos or images, the new IE 7 appears to require the ETag header. You will need to make sure that you follow the specifications for how ETag works in order for your cache control to work properly. Mozilla supports the ETag header as well, but does NOT require it for caching. If you need to cache a dynamic image, video, or other binary file, then be sure to set your ETag and then check for the If-Not-Modified header on subsequent requests so that you can properly return the 304 Not Modified page.

john (28-Mar-2006 04:36)

In addition to the above, don't forget to check the php.ini file for the setting: session.cache_limiter = nocache Since I use xoops and didn't start the session, I had the SSL/download problem until I noticed this.

(19-Oct-2005 04:11)

The onLoad method of Actionscript's loadVars class was returning false in IE6 using SSL until I set --> session_cache_limiter("must-revalidate"); <-- on the receiving PHP script.

radu dot rendec at ines dot ro (18-Oct-2005 12:41)

I've read the other comments and done some "reasearch" on my own. Using php's session mechanism and explicitly setting the "cache-control" header should not be mixed. When session_start() is called, the "cache-control" and "pragma" headers are automatically set by php (to whatever value had been specified using session_cache_limiter()). Explicitly setting those headers _before_ session_start() will have no effect, and explicitly setting them _after_ session_start() will overwrite the settings from session_cache_limiter(). If I had to deal with php sessions, I'd go for using session_cache_limiter() and leaving the headers alone.

(02-Sep-2005 11:04)

Andrei Chirila, andrei_chirila at yahoo dot com 12-Jan-2005 09:30 I played about an hour with the download and sessions. yes, to work you'll need session_cache_limiter("must-revalidate"); but this BEFORE session_start() if you want that your download start [IE problem]. Hope someone will need this someday ==== yes, somebody has needed this today :) situation: trying to make a session based download management system complete with user login system that requries an authorized user to download some files, and hide all such files from non-authorized users. the user login, download center, and content management system of the site are all tied in to each other, making troubleshooting this headering stuff a headache. problem: files being served are not accessible thru the regular site, since they are above the htdocs folder in apache, and so headering the file is required, and sessions do not work well with files being headered to the browser. solution: the download center uses ob_start("");, then session_cache_limiter("must-revalidate");, before the session_start();, then everything works well. thank you very much! i was resorting to using a cookie to control this before because i could not figure out how to tie in sessions to the system before!

donovan at go4 dot com dot au (08-Aug-2005 02:41)

IE6 'the file could not be written to the cache': I tried all the other suggestions mentioned here but none of them worked. I friend suggested header("Pragma: "); This worked straight away!

snakes at ntica dot com (12-May-2005 10:28)

Avoiding caching PHP pages: After lot of tries and research this is the best combination of headers I've found that seems to work well even with the proxy of visitors that are using satellit connection. <? header("ETag: PUB" . time()); header("Last-Modified: " . gmdate("D, d M Y H:i:s", time()-10) . " GMT"); header("Expires: " . gmdate("D, d M Y H:i:s", time() + 5) . " GMT"); header("Pragma: no-cache"); header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate"); session_cache_limiter("nocache"); ?>

Andrei Chirila, andrei_chirila at yahoo dot com (12-Jan-2005 02:30)

I played about an hour with the download and sessions. yes, to work you'll need session_cache_limiter("must-revalidate"); but this BEFORE session_start() if you want that your download start [IE problem]. Hope someone will need this someday ...

justin at justintubbs dot com (07-Jan-2005 08:04)

I have PHP 4.3 running on a Windows 2003 Server running IIS 6.0 also using SSL encryption for my pages. I could not (for the life of me) figure out how to get IE 6.0/WinXPPro to recognize a set of HTML tables as an Excel spreadsheet export, and it was due to the header() variables I was using. Hopefully these are helpful to others who are attempting the same type of export within PHP. *This example builds on the previously submitted one, adding a few necessary headers. <?php header("Expires: Sat, 01 Jan 2000 00:00:00 GMT"); header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT"); header("Pragma: public"); header("Expires: 0"); header("Cache-Control: must-revalidate, post-check=0, pre-check=0"); header("Cache-Control: public"); header("Content-Description: File Transfer"); session_cache_limiter("must-revalidate"); header("Content-Type: application/vnd.ms-excel"); header('Content-Disposition: attachment; filename="fileToExport.xls"'); // and after you start the session session_start(); ?>

pulstar at ig dot com dot br (24-Oct-2004 10:39)

You can find more information about to control the cache in PHP at http://www.php.net/manual/en/function.header.php If you have a dinamic website and want to allow your visitors to use the back button after they sent a form with the post method, the best combination I found was: <?php header("Expires: Sat, 01 Jan 2000 00:00:00 GMT"); header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT"); header("Cache-Control: post-check=0, pre-check=0",false); session_cache_limiter("must-revalidate"); // and after you start the session session_start(); ?> I try some combinations using header("Cache-Control: no-cache, must-revalidate"), but when clicking the back button, the last changes in the form back to their previous states. The combination above works fine with IE 6.x. I didn't test this with other browsers. When I try something like session_cache_limiter("nocache, must-revalidate") it doesn't work. The page only updates when I used the browser's refresh button. In dynamic web sites this is not good. The content must be fresh after each click. I didn't find these combinations like "private, must-revalidate" documented in the manual and I guess that something different from "none, nocache, private, public and private_no_expire" are resolved to "none" or something like that. One thing I notice is that in session_cache_limiter() it is "nocache", but in header() it is "no-cache". This may give us some clues about how session_cache_limiter() function works. About caching, the perfect solution I think is to give the correct expiration date and time and also the right last-modified header for each element in the web site, when they are really updated. This means a lot of extra controls of course, but may worth in web sites with high overload. The "public" option means that all available cache in proxies and clientes will be used, so this improves the speed of the web site and also reduces the used bandwidth. But without the right expiration and last-modified headers, you can use it only in static web sites. The "private" option means that only the cache in clients will be used. This is good for a more sensitive data that can be stored locally in the browser cache. It have some benefits of the public option, but the same restrictions too. The "nocache" (or no-cache?) option means that the HTML portion will not be cached, but the images, CSS and JS files will. This is good for dynamic websites because you still can use the power of cache without loose the refreshness after each click. These files can be updated when you open the web site or use the browser's refresh button. I don't know why, but flash files are never updated when you click the refresh button. A common solution for this is to change the file name when you update the flash file. The "no-store" option means that all the content will not be cached anyway, including images, CSS or JS files. I don't know if this applyes to flash files too, but is possible. This option must be used with very sensitive data. I think the SSL uses this by default.

misterp3d at hotmail dot com (18-May-2004 10:16)

I had a problem using a FORM with POST method when user of my website was using the back button. The page requested a refresh to be able to see again the FORM. To solve the problem I used : <?php session_cache_limiter('private, must-revalidate'); ?> *You need to write this line before any output Hope that will help some of you ;) [P]

usenet at phord splat com (26-Mar-2004 04:44)

Hey! NickyBoy was right! I looked all over google and his note was the only place that had it right. But, there's a caveat. I wrote up my results here: http://www.phord.com/experiment/cache/

richard at izyn dot co dot nz (02-Mar-2004 02:17)

I found that session_cache_limiter("none") works for me when I create PDFs on the fly because session_cache_limiter("private") causes the browser(IE6) to cache the PDF indefinitely.

Mikko Hmlinen (22-Jan-2004 05:10)

I had a similair problem (browsers couldn't save files coming from my download-script). Only in my case the problem occured with IE 6.0 and Netscape 7.1. Adding the "session_cache_limiter('public');" before "session_start();" helped.

jthome at fcgov dot com (04-Dec-2003 12:36)

In addition to the note above regarding SSL/IE bug/Sessions, also make sure you DO NOT SET THE HEADER 'Pragma: no-cache' if you are sending an inline document (e.g., PDF document). For example: <?php header("Content-Type: application/pdf"); header("Content-Disposition: inline; filename=foo.pdf"); header("Accept-Ranges: bytes"); header("Content-Length: $len"); header("Expires: 0"); header("Cache-Control: private"); // header("Pragma: no-cache");//don't send this header!! ?> Best, -- Jim

plyrvt at mail dot ru (Yura Pylypenko) (31-Jul-2003 10:33)

Be careful using session_cache_limiter() with ob_start('ob_gzhandler') If ob_start('ob_gzhandler') is called after session_cache_limiter() it seems to overwrite cache control headers with 'nocache' equivalent. So always put ob_start first.

MerlinsInvite (23-May-2003 05:51)

I solved the problem with pushing downloads to browser's, without needing to play with server/session parameters by using : header("Content-Disposition: inline; filename=\"$filename\""); for IE browsers and header("Content-Disposition: attachment; filename=\"$filename\""); for all other browsers.

nickyboy at 4ce.co.uk (11-Mar-2003 01:42)

The problems people mention about IE are actually a feature! Microsoft Knowledge Base Article 316431 says: In order for Internet Explorer to open documents in Office (or any out-of-process, ActiveX document server), Internet Explorer must save the file to the local cache directory and ask the associated application to load the file by using IPersistFile::Load. If the file is not stored to disk, this operation fails. When Internet Explorer communicates with a secure Web site through SSL, Internet Explorer enforces any no-cache request. If the header or headers are present, Internet Explorer does not cache the file. Consequently, Office cannot open the file. They say this applies to: Microsoft Internet Explorer 5.5 for Windows 2000 Microsoft Internet Explorer 5.01 for Windows 2000 Microsoft Internet Explorer version 6 for Windows 2000 not sure about other versions! hth nickyboy

phobo at paradise.net.nz (13-Dec-2002 01:33)

Please note that you DO NOT NEED to specify session_cache_limiter to get downloads work IMHO. With IE6 (and others I imagine), you might have a problem with the filename attribute of Content-Disposition being recognised. In my experience, IE always believed the filename of the download was the name of the script (ie, the URL generating the file, rather than the header being pushed). When adding: Header("Pragma: public"); this was solved. E.g. (Working CSV / opens in Excel in Windows). -- header("Cache-control: private"); header("Content-Type: text/plain"); header("Content-Disposition: attachment; filename=\"$filename\""); header("Pragma: public"); echo "Dogs,Cats,Fish\n"; echo "1,2,3\n"; echo "4,5,6\n"; --

cj at NOSPAMceejayoz dot com (18-Jun-2002 07:41)

Setting session.cache_limiter = none; in your php.ini file will avoid the problem in IE in which pressing the back button after using a POST form will result in "Warning: Page Has Expired".

chris at cwcomputerservices dot co dot uk (20-May-2002 07:40)

IMPORTANT - READ THIS TO SAVE A LOT OF WASTED TIME After spending a long time trying all the above solutions without success, I eventually found a more likely cause for these errors. There are problems with Apache/SSL and Internet Explorer with SSL connections - detailed information and a simple fix is here: http://www.extremetech.com/article/0,3396,s=201&a=24899,00.asp and here: http://www.modssl.org/docs/2.8/ssl_faq.html#ToC49 So a simple web server reconfiguration may save you hours of fiddling with cache control headers!

roblugt at elcel dot com (10-Oct-2001 02:04)

We had a strange problem with zip file downloads (not using SSL) under IE5. If the user chose the option to "save to disk", then everything worked fine, but if they chose "open", then winzip was launched okay - but the displayed zip archive was empty. We eventually tracked this down to the Cache-Control header and the php script was fixed by adding session_cache_limiter('public'); before the first call to session_register()

simon at ateb dot co dot uk (02-Mar-2001 06:49)

There is a bug(?) in Internet Explorer v5.5 to do with file downloads over a secure (https) web connection when using sessions. If you have a php script which delivers files for downloading by setting headers for the content-type etc. from a URL like this: getfile.php/filename.ext - or - getfile.php?file=/filename.ext and that script uses sessions, then you must explicitly set session_cache_limiter('public'); *before* you use session_start(); otherwise you will get one of the following errors from IE when it attmpts to download the file: Internet Explorer cannot download filename.ext from name.of.your.webserver Internet Explorer was not able to open this site. The requested site is either unavailable or cannot be found. Please try again later. Mmm, this is useful error message isn't it! The other error you will see when right clicking and choosing 'Save Target As...' gives the error Internet Explorer cannot download filename.ext from name.of.your.webserver The file could not be written to the cache. This problem does not occur over unsecure (http) links and files download OK. I don't know why this should be the case, but PHP seems to send an extra no-cache header when using sessions which breaks IE when it is using SSL. Setting the session_cache_limiter turns off this behaviour.

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