Header, Expires, Cache-Control, Pragma - what the **** is this?

halojoy

hello again.
halojoy here.

I have never understood the header() function, really
I have a script contact me at my website. It is a modified free Guestbook I downloaded.
It works great!
But there is one thing I do not understand.
Header, Expires, Cache-Control, Pragma - what the **** is this?

Before my Form Page is displayed, this is performed by PHP

<?php
////// Contact FORM display START
// Take care of signup form not caching
header( 'Expires: Mon, 26 Jul 2000 05:00:00 GMT' );
header( 'Cache-Control: no-store, no-cache, must-revalidate' );
header( 'Cache-Control: post-check=0, pre-check=0', FALSE );
header( 'Pragma: no-cache' );
printHEADER();
?>
<br><br>
<form action='' method='POST'>
<table class='form' cellspacing='0' cellpadding='4'>
<tr><td align='center'><a href='./'>Contact halojoy</a></td></tr>
<tr><td>
<table cellspacing='0' cellpadding='3'>
<tr><td><b>Your Name:</b></td><td><input type='text' name='name' size='30' maxlength='30'></td></tr>
<tr><td>City / Country:</td><td><input type='text' name='from' size='30' maxlength='30'></td></tr>
<tr><td>Your Email:</td><td><input type='text' name='email' size='30' maxlength='50'></td></tr>
<tr><td>Your Website:</td><td><input type='text' name='url' value='http://' size='40' maxlength='80'></td></tr>
<tr><td>Your IPaddress:</td><td><?php echo $_SERVER['REMOTE_ADDR'] ?></td></tr>
<tr><td colspan='2'><b>Comments:</b><br><textarea name='comments' rows='9' cols='50'></textarea><br>
<input type='submit' name='submit' value='Submit'></td></tr>
</table></td></tr></table></form>
<?php
printFOOTER();
exit();
?>

Quote:
Take care of signup form not caching ???

This Header thing DOES NOT SHOW in my HTML Form source.
So, what will I risk, by removing this header thing?
I do not want any code, that just takes time to load, in my pages.
Does this Pragma-Expires-Cache-Control do anything good?

/halojoy
😕 wants to know - ALL about Headers in PHP 😕

edcellgavin

it tells the browser not to cache the page's content, useful for dynamic pages which changes a lot. also, you may want to read header

halojoy

Originally posted by edcellgavin
- it tells the browser not to cache the page's content
...( useful for dynamic????( what is dynamic ) pages which changes a lot )
- a link to a reference at php.net

Thanks for the LINK to A Valid Reference, Ed Cell Gavin.
Good for me to be able to see, you all will not give me FALSE information here. 🙂
But PHP Manual is written in a sort of technical language.
And in a sort of foreign language to me. I speak my motherland language of swedish.
I wanted some humans to give me some practikally info, I could easily understand ( absorb ).

Plain AND/OR brooken english, Please!

So, 'it' tells 'somebody' not to 'cache' my form page.
This gives me 4 questions ( related to my Topic's All Questions )

1. What does 'it' refer to?
2. Who is this 'somebody' caching my form?
3. What is bad with eventual 'cacheing'?
4. How big is risk, I get problem, when somebody will 'cache' my form?

I removed all this header stuff.
Can see no what so ever difference in looks of page or anything else notisable. Not to me.

halojoy - thinks this TOPIC is far from resolved, yet
halojoy - writes, spreches und comprendes brooken english
as perfekt as any english children of the older of 8 years
because halojoy learnt him anglias into one swedish school, many years ago, when he were most young
:p

halojoy

Here is the highlighted 'full php code' - if to any help to answer my questions -
to my contactme.php including this form
show code of halojoy contactme.php

how form looks ( without cacheing )
screenshot of header( no-cache ) contact form

( I have also written 'showcode.php' script myself !! )
/halojoy 🆒
....

show code of this header cache thread using halojoy script

edcellgavin

it - the header() function
the browser cache web pages
consider viewing a static page with tons of images and files associated with it. what the browser do is to save temporary copies of those files so that the browser will not retrieve those files everytime the page is viewed.
it's not actually a problem but a preference depending on your system requirements. if your content changes a lot and you would want fresh information fetched from the server everytime, your script (by way of header()) should tell the browser not to cache the page you're serving. So that the next view on the same page will result in the browser fetching the data from the server instead of fetching in the temporary internet files in the client's harddisk.

halojoy

Oboy.

Can anybody else
who really know a good answer to this question
please enlighten me.

Still do not know if there is some strange reason
for me to keep all those lines.

My specific questions are in my previous posts.
I want to get this resolved
by someone that can answer up to this dilemma.

Thanks
halojoy
😕

bradgrafelman

I understand you're from Sweden, so I'll try to explain this simply.

The software you use to view a webpage (Internet Explorer, Opera, Firefox, Netscape, etc.) can help you save time by caching, or downloading and saving, a certain web page. For people on slow modems, this can help since they don't have to download the webpage every time they visit it. Instead, their browser loads the saved, or 'cached', version of the page.

If you make changes to your page a lot, or if your page is dynamically created (i.e. made from changing data taken from a database, other source, etc.), this can be bad. Your viewers might be viewing an old cached (or saved) version of the page, and not see the new content!

HTTP headers are sort of like instructions to your browser - they tell your browser what to do. Think of it like this: if your boss at work tells you to make a graph of certain data, and gives you a list of instructions, you wouldn't type out those instructions onto the graph, would you? No, you would simply follow them and make the graph like the instructions say. HTTP headers do the same thing. Your browser doesn't print them on the page, it simply follows the instructions.

All of the headers you have in your code are aimed at preventing the caching (or 'saving') of your web page, so that it must be downloaded every time a person visits it.