Geometry->difference() crashes

[duvifn]

I originally opened this issue in gdal repository, but it turns out to be a geos error.
So open it here.

With the following code I expect to get the difference between two geometries

Instead I get the following error:

/usr/include/c++/7/debug/vector:424:
Error: attempt to subscript container with out-of-bounds index 2, but 
container only holds 2 elements.

Objects involved in the operation:
    sequence "this" @ 0x0x555555772548 {
      type = std::__debug::vector<geos::geom::Coordinate, std::allocator<geos::geom::Coordinate> >;
    }

which happens in this vector access

Steps to reproduce the problem.

Compile the following code with geos 3.8.0.

#include <iostream>
#include <memory>

#include <geos/geom/GeometryFactory.h>
#include <geos/geom/Geometry.h>
#include <geos/io/WKTWriter.h>
#include <geos/io/WKTReader.h>

struct Rectangle {
  double west = -180.0;
  double east = 180.0;
  double south = -90.0;
  double north = 90.0;
};
std::unique_ptr< geos::geom::Geometry >  CreateRectangleGeometry(const Rectangle& rect) {
  auto wkt_reader = geos::io::WKTReader();
  std::string wkt = "POLYGON((" + 
                    std::to_string(rect.west) + " " + 
                    std::to_string(rect.north) + ", " + 
                    std::to_string(rect.east) + " " + 
                    std::to_string(rect.north) + ", "+ 
                    std::to_string(rect.east) + " " + 
                    std::to_string(rect.south) + ", " + 
                    std::to_string(rect.west) + " " + 
                    std::to_string(rect.south) +", " + 
                    std::to_string(rect.west) + " " + 
                    std::to_string(rect.north) +
                    "))";
  auto geom = wkt_reader.read(wkt);
  return geom;

}

int main(int argc, char* argv[]){
  Rectangle rect;
  rect.west = 0.0;
  rect.east = 2.0;
  rect.south = 0.0;
  rect.north = 2.0;

  Rectangle rect2;
  rect2.west = 0.1;
  rect2.east = 4.0;
  rect2.south = 0.1;
  rect2.north = 1.9;
  
  auto geom1 = CreateRectangleGeometry(rect);
  auto geom2 = CreateRectangleGeometry(rect2);
  auto geom3 = geom2->difference(geom1.get());

  geos::io::WKTWriter writer;
  std::cout << writer.write(geom3.get());
  return 0;
}

Operating system

Ubuntu 18.04.2 LTS 64 bit

GEOS version

Self compiled GEOS 3.8.0.

[dr-jts]

Yup, looks like a bug, due to this commit: e1fd59f

Looks like the simplest fix is to move the assignment to curr to the top of the loop. @dbaston any chance you can fix this (and add a unit test!)

[pramsey]

Looks like it was already fixed, 2 weeks after release of 3.8.0 at 3fc6528

[dr-jts]

Good that it is fixed. A unit test would be nice (which should be easy to provide in XML).

[pramsey]

Tests are done and in PRs, will merge when CI gives me a thumbs up.

[pramsey]

Tests are in 3.8 and master now, next patch release will have this fix.

[pramsey]

Link for reference https://trac.osgeo.org/geos/ticket/1018

[duvifn]

@dr-jts @pramsey thanks!