Zero-size SVG rendering : mapserv.fcgi crashes

[FilipGh]

Actual behavior

I bumped into a configuration (zoom, orientation, ...) where an SVG symbol has one null dimension (height or width).
The rendering process crashes with the following error message (mapcairo.c):

mapserv.fcgi: /builds/i4d/datacenter/mapserver/MapServer/mapcairo.c:1074:
msRenderRasterizedSVGSymbol: Assertion "svg_cache->pixmap_buffer->height && svg_cache->pixmap_buffer->width" failed.

The code snippet shows:

//already rendered at the right size and scale? return
if(svg_cache->scale != style->scale || svg_cache->rotation != style->rotation) {
   ...
}
assert(svg_cache->pixmap_buffer->height && svg_cache->pixmap_buffer->width);

Expected behavior

Instead of crashing the rendering process, wouldn't it be more appropriate to test buffer dimensions beforehands.
Something like :

if ( (svg_cache->pixmap_buffer->height == 0 || (svg_cache->pixmap_buffer->width == 0) )
   return MS_FAILURE;

//already rendered at the right size and scale? return
if(svg_cache->scale != style->scale || svg_cache->rotation != style->rotation) {
   ...
}

Steps to reproduce the problem.

With the data in the attached ZIP, run the following command :
mapcache_seed -c /var/www/html/geo/mapcache_seed_G4D-506.xml -t G4D-506_meta -v -b -f -n8 -e 20.9068,32.5112,20.9104,32.5139 -z 1,17

Attached simple test case

The attached ZIP contains G4D-506.zip:

• G4D-506.gpkg : contains the vector layer to be rendered
• WMS_G4D-506.map : map file with the rendering parameters (especially the SVG symbol)
• P00067_Dk-Brown1815_Tick.svg : SVG symbol
• mapcache_seed_G4D-506.xml : map cache file for mapcache_seed executable

You can modify symbol size to make the test OK or NOK (see WMS_G4D-506.map):

STYLE
   SYMBOL "P00067_Dk-Brown1815_Tick.svg"
   # If SIZE=40: no bug
   # If SIZE=4: bug in mapcairo.c:1074
   SIZE 4
   GAP -7.5
   INITIALGAP 3.75
END #STYLE

Operating system

Centos Linux release 7.2.1511

MapServer version and installation method

• Mapserver 7.6.3
• MapCache : 1.12.0

PROMPT > mapserv -v
MapServer version 7.6.3 OUTPUT=PNG OUTPUT=JPEG OUTPUT=KML SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=CAIRO SUPPORTS=SVG_SYMBOLS SUPPORTS=RSVG SUPPORTS=ICONV SUPPORTS=XMP SUPPORTS=FRIBIDI SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER SUPPORTS=FASTCGI SUPPORTS=THREADS SUPPORTS=GEOS SUPPORTS=POINT_Z_M SUPPORTS=PBF INPUT=JPEG INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
PROMPT >