WebStack

Annotated docs/headers.html

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2005-11-15 paulb file changeset files shortlog [project @ 2005-11-15 15:46:01 by paulb] Added has_key method.
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head>
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  <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type" />
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  <title>Request Headers</title><meta name="generator" content="amaya 8.1a, see http://www.w3.org/Amaya/" />
 
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  <link href="styles.css" rel="stylesheet" type="text/css" /></head>
 
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<body>
 
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<h1>Request Headers</h1>
 
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<p>Request headers are pieces of information that describe certain aspects of a request, such as:</p>
 
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<ul>
 
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  <li>The location to which the request is being sent.</li>
 
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  <li>The type of information in the request body.</li>
 
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  <li>Preferences about which kinds of information the sender would like to receive in return.</li>
 
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</ul>
 
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<p>The location and&nbsp;related query information is conveniently accessible through <a href="paths.html">path</a> information and <a href="parameters-headers.html">request header parameter</a> information. Other types of header information are made available through other WebStack API methods.</p>
 
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<h2>Content Types</h2>
 
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<p>When a Web application sends some information in a response, it
 
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describes the content type of that information, and this is described
 
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in the "Responses and Presentation" document. However, it is also
 
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possible that information sent to the application is also described
 
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using a content type, and such details may be investigated using code
 
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similar to the following:</p>
 
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<pre>class MyResource:<br />    def respond(self, trans):<br />        content_type = trans.get_content_type()   # returns a WebStack.Generic.ContentType object</pre>
 
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<p>Unfortunately, such information is not always provided by Web browsers.</p>
 
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<h2>Content Preferences</h2>
 
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<p>Sometimes, Web browsers&nbsp;describe the kinds of information that
 
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they are willing to receive, and WebStack provides various means to
 
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query such preferences:</p>
 
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<pre>        languages = trans.get_content_languages() # returns a list of language codes<br />        charsets = trans.get_content_charsets()   # returns a list of character set identifiers<br /></pre>
 
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<p>This information permits us to send content which matches the
 
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expectations of the user, or at least the expectations of the user's
 
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software.</p>
 
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<h2>Other Headers</h2>
 
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<p>Various other pieces of information may be attached to the request
 
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as headers, and such information can be accessed through the general
 
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header access methods as described below. Each header has a particular
 
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name which is associated with a corresponding value.</p>
 
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<div class="WebStack">
 
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<h3>WebStack API - Accessing Header Information</h3>
 
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<p>Transaction objects provide the following methods to access request header information:</p>
 
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<dl>
 
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  <dt><code>get_headers</code></dt>
 
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    <dd>This returns a
 
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      dictionary mapping header names to single string values.<br />
 
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</dd>
 
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  <dt><code>get_header_values</code></dt>
 
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    <dd>Given a header name as parameter, this method returns a list of string values associated with that name.</dd><dt><code>get_content_type</code></dt>
 
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  <dd>This returns a content type object (typically&nbsp;<code>WebStack.Generic.ContentType</code>) describing the incoming request body content.</dd>
 
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  <dt><code>get_content_languages</code></dt>
 
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  <dd>This returns a list of language identifiers, in descending order
 
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of preference, indicating in which languages the sender of the request
 
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would prefer to receive information.</dd>
 
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  <dt><code>get_content_charsets</code></dt>
 
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  <dd>This returns a list of character set identifiers, in descending
 
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order of preference, indicating in which character sets the sender of
 
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the request would prefer to receive information.</dd>
 
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</dl>
 
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<p>It should be noted that the&nbsp;<code>get_headers</code> and <code>get_header_values</code>&nbsp;methods
 
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present a slightly different view of the available header information,
 
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in that only a single header value is made available through the <code>get_headers</code>&nbsp;method for each header name, whereas&nbsp;<code>get_header_values</code> provides potentially many values for the same header name. </p>
 
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</div></body></html>