====== MapServer upgrade from Debian 11 to Debian 12 ======

Finally I decided to upgrade my home server from **Debian 11 Bullseye** to **Debian 12 Bookworm**; here you can read some notes about the upgrade: **[[debian_upgrade_11_12]]**.

One change that deserves a dedicated page is the upgrade from **MapServer 7.6.2** shipped with Debian 11 to **MapServer 8.0.1** shipped with Debian 12; in fact it happened that almost all the MapServer based applications stopped working.

===== Mandatory /etc/mapserver.conf =====

In version 8 it became mandatory to have a configuration file, the default location of which is **/etc/mapserver.conf**. See the syntax here: [[https://mapserver.org/mapfile/config.html]]. You must declare at least the ''MS_MAP_PATTERN'' path.

==== CONFIG:MAPS aliases ====

In the past I used to have some CGI-Mapserver services (as native MapServer or as WMS service) where the service URL contained **the full path of the mapfile**, something like this:

<code>
http://www.rigacci.org/cgi-bin/mapserv?map=/usr/local/lib/mapserver/mie-strade-wms.map&
</code>

It is not a good practice to accept from the internet a parameter that is the full path to a local file. MapServer 8 requires that you declare at least a pattern that the received mapfile must obey to (''MS_MAP_PATTERN''). Better than that, you can define several aliases (short names pointing to the mapfiles wherever they resied) and **accept from the client only that aliases**, disallowing the requests for a full path mapfile (''MS_MAP_NO_PATH''). I opted for the latter mode:

<file>
# MapServer 8.0 Config File
# https://mapserver.org/mapfile/config.html
CONFIG
  MAPS
    # Define the aliases for mapfile paths.
    MIE_STRADE_WMS "/usr/local/lib/mapserver/mie-strade-wms.map"
  END
  ENV
    # Disallow using full path for mapfiles (use aliases defined in CONFIG:MAPS instead).
    MS_MAP_NO_PATH "true"
    # Limit mapfile access when using full paths, this setting is never used 
    # if CONFIG:ENV:MS_MAP_NO_PATH is set.
    MS_MAP_PATTERN "^/usr/local/lib/mapserver"
  END
END
</file>

In this way the above URL will be changed into:

<code>
http://www.rigacci.org/cgi-bin/mapserv?map=MIE_STRADE_WMS&
</code>

===== MAP:TRANSPARENT not longer valid =====

In MapServer 8 mapfiles the **TRANSPARENT** identifier is not longer accepted inside the MAP object, you have to move it into the **OUTPUTFORMAT** object; something like this:

<file>
  OUTPUTFORMAT
    NAME agg_png
    DRIVER "AGG/PNG"
    MIMETYPE "image/png"
    IMAGEMODE RGBA
    EXTENSION "png"
    TRANSPARENT ON
  END
</file>

===== Name change of CGI parameters =====

One of the biggest problem of the upgrade is the change of the name of some CGI parameters; notably the **map_size** option is not longer supported.

I had web application based on OpenLayers 2.11, which included a MapServer bitmap layer. The JavaScript code automatically generates the request URL, something like this (parameters are split on different lines for readability):

<code>
/cgi-bin/mapserv?map=/usr/local/lib/mapserver/mie_strade.map
    &format=image%2Fpng
    &mode=map
    &map_imagetype=png
    &mapext=1235758.1079621+5432310.5814201+1242666.1043925+5443174.1940635
    &imgext=1235758.1079621+5432310.5814201+1242666.1043925+5443174.1940635
    &map_size=1446+2274
    &imgx=723
    &imgy=1137
    &imgxy=1446+2274
</code>

Unfortunately the **map_size** option is not longer accepted and the resulting PNG image has the default size declared into the MAP:SIZE object of the mapfile, instead of the requested 1446x2274 pixels. This causes a **totally distorted map** image into the web application!

This problem cannot be easily fixed, because the URL options are hard-coded into the OpenLayers code. So I had to replace all the OpenLayers 2.x code with the current **OpenLayers 8.x**, which required a total refactory of the code.