can any one able to explain 'the HTTP functions in PHP' ?

Hi,
Actually these functions let you manipulate the output sent back to the remote browser right down to the HTTP protocol level.

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Hi,
header() is one of the HTTP functions.

header() is used to send raw HTTP headers.

Syntax is:

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The optional replace parameter indicates whether the header should replace a previous similar header, or add a second header of the same type. By default it will replace, but if you pass in FALSE as the second argument you can force multiple headers of the same type. For example:

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The second optional http_response_code force the HTTP response code to the specified value.

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There are two special-case header calls. The first is a header that starts with the string "HTTP/" (case is not significant), which will be used to figure out the HTTP status code to send. For example, if you have configured Apache to use a PHP script to handle requests for missing files (using the ErrorDocument directive), you may want to make sure that your script generates the proper status code.

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The HTTP status header line will always be the first sent to the client, regardless of the actual header() call being the first or not. The status may be overridden by calling header() with a new status line at any time unless the HTTP headers have already been sent.

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Example:

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The second special case is the "Location:" header. Not only does it send this header back to the browser, but it also returns a REDIRECT (302) status code to the browser unless some 3xx status code has already been set.

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example for the above is:

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Session ID is not passed with Location header even if session.use_trans_sid is enabled. It must by passed manually using SID constant.

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PHP scripts often generate dynamic content that must not be cached by the client browser or any proxy caches between the server and the client browser. Many proxies and clients can be forced to disable caching with:

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You may find that your pages aren't cached even if you don't output all of the headers above. There are a number of options that users may be able to set for their browser that change its default caching behavior. By sending the headers above, you should override any settings that may otherwise cause the output of your script to be cached.

Additionally, session_cache_limiter() and the session.cache_limiter configuration setting can be used to automatically generate the correct caching-related headers when sessions are being used.

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Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP. It is a very common error to read code with include(), or require(), functions, or another file access function, and have spaces or empty lines that are output before header() is called. The same problem exists when using a single PHP/HTML file.

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As of PHP 4, you can use output buffering to get around this problem, with the overhead of all of your output to the browser being buffered in the server until you send it. You can do this by calling ob_start() and ob_end_flush() in your script, or setting the output_buffering configuration directive on in your php.ini or server configuration files.

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If you want the user to be prompted to save the data you are sending, such as a generated PDF file, you can use the Content-Disposition header to supply a recommended filename and force the browser to display the save dialog.

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If safe mode is enabled the uid of the script is added to the realm part of the WWW-Authenticate header if you set this header (used for HTTP Authentication).

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Hi,

The HTTP Problem

Most writings on AJAX limit their discussion to HTTP's two main verbs: GET and POST, but there are 5 others (PUT, DELETE, HEAD, OPTIONS, TRACE) and they can have real value for serious application developers. Unfortunately few AJAX toolkits offer support for HTTP's full verb set. In fact, GET and POST are supported via Form submission so if you're just going to do GET/POST in an asynchronous format you've gained almost nothing over what browsers have been able to do for a decade.

To get full value out of XMLHTTPRequest you need to be able to control both the command verb and the HTTP headers that are sent so you retain control over how calls are made and how the server is likely to respond to them. You also need complete control over data encoding so you can adapt as needed to the various services you may have to integrate with. As with "The Sync Problem" this is another area where most AJAX toolkits fall down on the job.

Dealing with the full spectrum of HTTP and HTTPS options, as well as things like redirects is critical to any Enterprise-Class solution.

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Senraj.A

Hi,

headers_list() Function Definition and Usage

The headers_list() function returns a list of response headers sent (or ready to send) to a client.

This function returns an array of headers.

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Hi,

To determine whether or not the headers have been sent yet, use the headers_sent() function.

Example
---------
<?php
setcookie("TestCookie","SomeValue"');
header("X-Sample-Test: foo");
header('Content-type: text/plain');
?>

<html>
<body>

<?php
// What headers are to be sent?
var_dump(headers_list());
?>

</body>
</html>

The output of the code above will be:

array(4)
{
[0]=> string(23) "X-Powered-By: PHP/5.1.1"
[1]=> string(19) "Set-Cookie: TestCookie=SomeValue"
[2]=> string(18) "X-Sample-Test: foo"
[3]=> string(24) "Content-type: text/plain"
}

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Senraj.A