[Qgis-developer] QGIS Server Python Plugins API

[Alessandro Pasotti]

2014-10-23 20:20 GMT+02:00 G. Allegri <giohappy at gmail.com>:
> Hi Alessandro,
> I've read the latest version of the QEP and had a look to your repo.
> If I'm not wrong the current implementation doesn't provide custom services
> as in the initial proof of concept, but gives the opportunity to define
> "middlewares" before and after the requests have been processed by the
> standard OGC servces offered by QGIS Server. Is it right?
>
> giovanni
>

Hi Giovanni,

Thank you for your interest in my work!

You are partially right: the new implementation we agreed upon in
Hessen is loosely based on the Django concept of middlewares, with the
addition of the possibility to add new hooks (callbacks) in the
future.

This implementation also allows for an easy implementation of custom
services though.

In fact, this concept proved to be extremely flexible and unobtrusive
at the same time: a plugin can define one or more "filters" [1] with
an optional priority, the filters have access to server interface [2]
that in turn can manipulate the request handler [3].
By manipulating the requet handler, a plugin can intercept and alter
the input (typically the query string) **before** entering the main
C++ switch for core services and/or can intercept and alter the output
**after** the main C++ switch. The output typically is one of: none
(in case the service did not match), an exception, an image or a
XML/HTML document.

I have developed a test plugin [4] which implements the following filters:

* an HTML remote python console, also implements HTTP BASIC
Authentication to give an example of HTTP header manipulation
* do nothing but logging the result of QUERY STRING manipulation tests</li>\n"
* say HelloServer! and write some lines in the logs
* WaterMarkFilter: adds a watermark image on top of all WMS GetImage requests
* raise and exception, catched in main loop

Have a look to the filters for the implementation details.

For anyone interested in testing, the implementation is in my
"serverpython" branch:

https://github.com/elpaso/QGIS/tree/serverpython

PLEASE NOTE THAT in a previous email I gave the address of a wrong
branch, that one above is the right one.:

[1] http://www.itopen.it/qgis/serverplugins/api/classQgsServerFilter.html
[2] http://www.itopen.it/qgis/serverplugins/api/classQgsServerInterface.html
[3] http://www.itopen.it/qgis/serverplugins/api/classQgsRequestHandler.html
[4] https://github.com/elpaso/qgis-helloserver/tree/master/filters

-- 
Alessandro Pasotti
w3:   www.itopen.it