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