Golpha/redirects.md

## redirects.md

      
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              redirects.md
            
          
    Hypertext Transfer Protocol Redirect Methods

Redirecting with PHP

The most common way to execute redirects with PHP is to send headers to the client. This can be easily done with the header-Method of PHP.
<?php

header('location: http://www.example.org/foo/bar');

To avoid protocol collisions ( e.g. sending headers after a response body ) you may check the current state of your response and send only header informations if the protocol allows them:
<?php

if ( ! headers_sent($file, $line) ) {
   header('location: http://www.example.org/foo/bar');
}
else {
   echo 'Could not redirect you, headers are allready send in ['.$file.'] on line #'.$line.'.';
}

Protocol Standard: To send headers is the only method to ensure the execution of an redirect. HTTP/1.1 is an world wide implemented standardized protocol.
Redirect with (x)HTML(5)

Another way to redirect safetly without taking care about any HTT-Protocol-Issue is to emulate an http-response refresh-header-field with meta-tags inside of your (x)HTML-Document ( respect the syntax difference of xHTML and HTML, the following source is HTML5 ):
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Redirecting</title>
    
    <meta http-equiv="refresh" content="5; http://www.example.org/foo/bar">
  </head>
  <body>
    <p>Redirecting you to the next page, please wait... 
    If nothing happens please click <a href="http://example.org/foo/bar">here</a>.</p>
  </body>
</html>

The meta-tag serves an http-equiv-property that defines the http-protocol header-field equivalent of the contained string:refresh ( instead of location ). The content-property defines the time in seconds after the redirect should appear and the url to redirect to seperated by a single ;.
Be careful: meta-tag behaviour depends completely on the web browser inplementation of web document standards. There is no warranty that the browser executes your http-equiv meta-definition.
Javascript Redirect

The last and lesser recommend method to redirect an webpage to another is to use javascript:
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Redirecting</title>
    
    <script type="text/javascript">
      function domready() {
        window.location.href = 'http://www.example.org/foo/bar';
      }
    </script>
  </head>
  <body onLoad="domready();">
    
  </body>
</html>

Dependency Behaviour: Javascript is an optional mechanic at the client. There is in no case a warranty that javascript is enabled at the client. Redirecting with javascript is only recommend if your entire application bases on javascript ( your application won't work without javascript ). For webpages that only have comfort benefits, javascript-redirects are the worst way to redirect and should be avoided.