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<title>File: SPEC</title>
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<h1>SPEC</h1>
<table class="header-table">
<tr class="top-aligned-row">
<td><strong>Path:</strong></td>
<td>SPEC
</td>
</tr>
<tr class="top-aligned-row">
<td><strong>Last Update:</strong></td>
<td>Tue Feb 26 13:30:03 +0100 2008</td>
</tr>
</table>
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<div id="description">
<p>
This specification aims to formalize the <a
href="../classes/Rack.html">Rack</a> protocol. You can (and should) use <a
href="../classes/Rack/Lint.html">Rack::Lint</a> to enforce it. When you
develop middleware, be sure to add a Lint before and after to catch all
mistakes.
</p>
<h1><a href="../classes/Rack.html">Rack</a> applications</h1>
<p>
A <a href="../classes/Rack.html">Rack</a> application is an Ruby object
(not a class) that responds to <tt>call</tt>. It takes exactly one
argument, the <b>environment</b> and returns an Array of exactly three
values: The <b>status</b>, the <b>headers</b>, and the <b>body</b>.
</p>
<h2>The Environment</h2>
<p>
The environment must be an true instance of Hash (no subclassing allowed)
that includes CGI-like headers. The application is free to modify the
environment.
</p>
<p>
The environment is required to include these variables (adopted from
PEP333), except when they‘d be empty, but see below.
</p>
<table>
<tr><td valign="top"><tt>REQUEST_METHOD</tt>:</td><td>The HTTP request method, such as "GET" or "POST". This
cannot ever be an empty string, and so is always required.
</td></tr>
<tr><td valign="top"><tt>SCRIPT_NAME</tt>:</td><td>The initial portion of the request URL‘s "path" that
corresponds to the application object, so that the application knows its
virtual "location". This may be an empty string, if the
application corresponds to the "root" of the server.
</td></tr>
<tr><td valign="top"><tt>PATH_INFO</tt>:</td><td>The remainder of the request URL‘s "path", designating the
virtual "location" of the request‘s target within the
application. This may be an empty string, if the request URL targets the
application root and does not have a trailing slash.
</td></tr>
<tr><td valign="top"><tt>QUERY_STRING</tt>:</td><td>The portion of the request URL that follows the <tt>?</tt>, if any. May be
empty, but is always required!
</td></tr>
<tr><td valign="top"><tt>SERVER_NAME</tt>, <tt>SERVER_PORT</tt>:</td><td>When combined with <tt>SCRIPT_NAME</tt> and <tt>PATH_INFO</tt>, these
variables can be used to complete the URL. Note, however, that
<tt>HTTP_HOST</tt>, if present, should be used in preference to
<tt>SERVER_NAME</tt> for reconstructing the request URL.
<tt>SERVER_NAME</tt> and <tt>SERVER_PORT</tt> can never be empty strings,
and so are always required.
</td></tr>
<tr><td valign="top"><tt>HTTP_</tt> Variables:</td><td>Variables corresponding to the client-supplied HTTP request headers (i.e.,
variables whose names begin with <tt>HTTP_</tt>). The presence or absence
of these variables should correspond with the presence or absence of the
appropriate HTTP header in the request.
</td></tr>
</table>
<p>
In addition to this, the <a href="../classes/Rack.html">Rack</a>
environment must include these <a
href="../classes/Rack.html">Rack</a>-specific variables:
</p>
<table>
<tr><td valign="top"><tt>rack.version</tt>:</td><td>The Array [0,1], representing this version of <a
href="../classes/Rack.html">Rack</a>.
</td></tr>
<tr><td valign="top"><tt>rack.url_scheme</tt>:</td><td><tt>http</tt> or <tt>https</tt>, depending on the request URL.
</td></tr>
<tr><td valign="top"><tt>rack.input</tt>:</td><td>See below, the input stream.
</td></tr>
<tr><td valign="top"><tt>rack.errors</tt>:</td><td>See below, the error stream.
</td></tr>
<tr><td valign="top"><tt>rack.multithread</tt>:</td><td>true if the application object may be simultaneously invoked by another
thread in the same process, false otherwise.
</td></tr>
<tr><td valign="top"><tt>rack.multiprocess</tt>:</td><td>true if an equivalent application object may be simultaneously invoked by
another process, false otherwise.
</td></tr>
<tr><td valign="top"><tt>rack.run_once</tt>:</td><td>true if the server expects (but does not guarantee!) that the application
will only be invoked this one time during the life of its containing
process. Normally, this will only be true for a server based on CGI (or
something similar).
</td></tr>
</table>
<p>
The server or the application can store their own data in the environment,
too. The keys must contain at least one dot, and should be prefixed
uniquely. The prefix <tt>rack.</tt> is reserved for use with the <a
href="../classes/Rack.html">Rack</a> core distribution and must not be used
otherwise.
</p>
<p>
The environment must not contain the keys <tt>HTTP_CONTENT_TYPE</tt> or
<tt>HTTP_CONTENT_LENGTH</tt> (use the versions without <tt>HTTP_</tt>). The
CGI keys (named without a period) must have String values.
</p>
<p>
There are the following restrictions:
</p>
<ul>
<li><tt>rack.version</tt> must be an array of Integers.
</li>
<li><tt>rack.url_scheme</tt> must either be <tt>http</tt> or <tt>https</tt>.
</li>
<li>There must be a valid input stream in <tt>rack.input</tt>.
</li>
<li>There must be a valid error stream in <tt>rack.errors</tt>.
</li>
<li>The <tt>REQUEST_METHOD</tt> must be one of <tt>GET</tt>, <tt>POST</tt>,
<tt>PUT</tt>, <tt>DELETE</tt>, <tt>HEAD</tt>, <tt>OPTIONS</tt>,
<tt>TRACE</tt>.
</li>
<li>The <tt>SCRIPT_NAME</tt>, if non-empty, must start with <tt>/</tt>
</li>
<li>The <tt>PATH_INFO</tt>, if non-empty, must start with <tt>/</tt>
</li>
<li>The <tt>CONTENT_LENGTH</tt>, if given, must consist of digits only.
</li>
<li>One of <tt>SCRIPT_NAME</tt> or <tt>PATH_INFO</tt> must be set.
<tt>PATH_INFO</tt> should be <tt>/</tt> if <tt>SCRIPT_NAME</tt> is empty.
<tt>SCRIPT_NAME</tt> never should be <tt>/</tt>, but instead be empty.
</li>
</ul>
<h3>The Input Stream</h3>
<p>
The input stream must respond to <tt>gets</tt>, <tt>each</tt> and
<tt>read</tt>.
</p>
<ul>
<li><tt>gets</tt> must be called without arguments and return a string, or
<tt>nil</tt> on EOF.
</li>
<li><tt>read</tt> must be called without or with one integer argument and
return a string, or <tt>nil</tt> on EOF.
</li>
<li><tt>each</tt> must be called without arguments and only yield Strings.
</li>
<li><tt>close</tt> must never be called on the input stream.
</li>
</ul>
<h3>The Error Stream</h3>
<p>
The error stream must respond to <tt>puts</tt>, <tt>write</tt> and
<tt>flush</tt>.
</p>
<ul>
<li><tt>puts</tt> must be called with a single argument that responds to
<tt>to_s</tt>.
</li>
<li><tt>write</tt> must be called with a single argument that is a String.
</li>
<li><tt>flush</tt> must be called without arguments and must be called in order
to make the error appear for sure.
</li>
<li><tt>close</tt> must never be called on the error stream.
</li>
</ul>
<h2>The Response</h2>
<h3>The Status</h3>
<p>
The status, if parsed as integer (<tt>to_i</tt>), must be bigger than 100.
</p>
<h3>The Headers</h3>
<p>
The header must respond to each, and yield values of key and value. The
header keys must be Strings. The header must not contain a <tt>Status</tt>
key, contain keys with <tt>:</tt> or newlines in their name, contain keys
names that end in <tt>-</tt> or <tt>_</tt>, but only contain keys that
consist of letters, digits, <tt>_</tt> or <tt>-</tt> and start with a
letter.
</p>
<p>
The values of the header must respond to each. The values passed on each
must be Strings and not contain characters below 037.
</p>
<h3>The Content-Type</h3>
<p>
There must be a <tt>Content-Type</tt>, except when the <tt>Status</tt> is
204 or 304, in which case there must be none given.
</p>
<h3>The Body</h3>
<p>
The Body must respond to each and must only yield String values.
</p>
<p>
If the Body responds to close, it will be called after iteration.
</p>
<p>
The Body commonly is an Array of Strings, the application instance itself,
or a File-like object.
</p>
<h2>Thanks</h2>
<p>
Some parts of this specification are adopted from PEP333: Python Web Server
Gateway Interface v1.0 (<a
href="http://www.python.org/dev/peps/pep-0333">www.python.org/dev/peps/pep-0333</a>/).
I‘d like to thank everyone involved in that effort.
</p>
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