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Provide infrastructure for plugging views that run directly at the ZServer thread

Project description

Introduction

This Zope add-on product provides for easy configuration of ZServer Views.

It was authored by Leonardo Rochael Almeida, and sponsored by OpenMultimedia.

A ZServer View is a (supposedly) small and fast WSGI application that runs directly from within the ZServer thread (a.k.a. medusa thread).

This means that a ZServer View will run even if all Zope worker-threads are busy handling other requests. It also means that if a ZServer View is not fast, then it is blocking the ZServer from handling incoming requests for all worker threads, so be mindful when using this product.

ZServer Views are mostly useful for system monitoring tools, like DeadlockDebugger or Zope resource monitoring.

Installation

Add Products.ZServerViews to the list of eggs of the part that defines your Zope instance.

Configuration

Add a product-config section for zserver-views to your Zope configuration (e.g. the zope.conf file or a zope-conf-additional parameter in your buildout configuration).

Each entry in this section should contain an identifier (must be unique within the section but are currently unused [1]), a URL path and the dotted name of the view which will be served from that URL path, all separated by whitespace. For example:

<product-config zserver-views>
    my-package /my/view my.package.mymodule.my_view
    thread-id /thr-id Products.ZServerViews.tests.common.current_thread_id_zserver_view
</environment>

This means that the http://yourserver/my/view URL will run the WSGI app at my.package.mymodule.my_view and the url at http://yourserver/thr-id will run the Products.ZServerViews.tests.common.current_thread_id_zserver_view WSGI view.

Query strings, if present, will be passed to the ZServer Views, but sub-paths will not. I.e., http://yourserver/my/view?foo=bar will run my.package.mymodule.my_view, but http://yourserver/thrid/fred will not run the Products.ZServerViews.tests.common.current_thread_id_zserver_view view, but will be handled by Zope directly.

This behaviour is intentional, and reflects the fact that ZServer View location is decided by a single dictionary lookup, instead of multiple regex or substring matching.

[1]The identifiers in product-config keys cannot be composed of many valid URL characters, and are forcibly lower-cased, so they’re useless for either the URL or the dotted name of the view.

Writing ZServer Views

ZServer Views are mini WSGI apps, which mean they take an env and a start_response parameter, and return the bytes that must be sent to the browser. The query string, if any, will be passed into env[‘QUERY_STRING’].

For HTTP/1.1 compatibility they must either pass a “Content-Lenght” header into start_response() or a “Transfer-Encoding=chunked” header and chunk the content. If neither is done, the response will fall back to HTTP/1.0 automatically, and the connection will be forced close.

To ease the creation of these mini apps, a decorator exists (Products.ZServerViews.base import TextView) that can wrap a function receiving only the env parameter and returns a single unicode string. This decorator will take care of all the WSGI conversation around that response.

Check Products.ZServerViews.tests.common.current_thread_id_zserver_view for an example.

Changelog

0.2.0 (2013-01-24)

  • Make the message of ViewError a mandatory parameter. It can be empty but lots of HTTP error codes require a body in the response, so an empty body is no longer the default [leorochael]
  • Add a modicum of Python 2.4/Zope 2.10 compatibility (Exceptions are not new-style classes) [leorochael]

0.1.1 (2013-01-18)

  • Include .rst files in the manifest [leorochael]

0.1.0 (2013-01-18)

  • Initial release

Project details


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