Refs #26789 -- Fixed output of WKBWriter for empty points and polygons.

django/contrib/gis/geos/prototypes/io.py

@@ -226,13 +226,37 @@ class WKBWriter(IOBase):
         super(WKBWriter, self).__init__()
         self.outdim = dim
 
+    def _handle_empty_point(self, geom):
+        from django.contrib.gis.geos import Point
+        if isinstance(geom, Point) and geom.empty:
+            if self.srid:
+                # PostGIS uses POINT(NaN NaN) for WKB representation of empty
+                # points. Use it for EWKB as it's a PostGIS specific format.
+                # https://trac.osgeo.org/postgis/ticket/3181
+                geom = Point(float('NaN'), float('NaN'), srid=geom.srid)
+            else:
+                raise ValueError('Empty point is not representable in WKB.')
+        return geom
+
     def write(self, geom):
         "Returns the WKB representation of the given geometry."
-        return six.memoryview(wkb_writer_write(self.ptr, geom.ptr, byref(c_size_t())))
+        from django.contrib.gis.geos import Polygon
+        geom = self._handle_empty_point(geom)
+        wkb = wkb_writer_write(self.ptr, geom.ptr, byref(c_size_t()))
+        if isinstance(geom, Polygon) and geom.empty:
+            # Fix GEOS output for empty polygon.
+            # See https://trac.osgeo.org/geos/ticket/680.
+            wkb = wkb[:-8] + b'\0' * 4
+        return six.memoryview(wkb)
 
     def write_hex(self, geom):
         "Returns the HEXEWKB representation of the given geometry."
-        return wkb_writer_write_hex(self.ptr, geom.ptr, byref(c_size_t()))
+        from django.contrib.gis.geos.polygon import Polygon
+        geom = self._handle_empty_point(geom)
+        wkb = wkb_writer_write_hex(self.ptr, geom.ptr, byref(c_size_t()))
+        if isinstance(geom, Polygon) and geom.empty:
+            wkb = wkb[:-16] + b'0' * 8
+        return wkb
 
     # ### WKBWriter Properties ###
 

tests/gis_tests/geos_tests/test_io.py

@@ -4,7 +4,8 @@ import binascii
 from unittest import skipUnless
 
 from django.contrib.gis.geos import (
-    HAS_GEOS, GEOSGeometry, Point, WKBReader, WKBWriter, WKTReader, WKTWriter,
+    HAS_GEOS, GEOSGeometry, Point, Polygon, WKBReader, WKBWriter, WKTReader,
+    WKTWriter,
 )
 from django.test import SimpleTestCase
 from django.utils.six import memoryview
@@ -155,3 +156,41 @@ class GEOSIOTest(SimpleTestCase):
 
         with self.assertRaisesMessage(AttributeError, 'WKT output rounding precision must be '):
             wkt_w.precision = 'potato'
+
+    def test_empty_point_wkb(self):
+        p = Point(srid=4326)
+        wkb_w = WKBWriter()
+
+        wkb_w.srid = False
+        with self.assertRaisesMessage(ValueError, 'Empty point is not representable in WKB.'):
+            wkb_w.write(p)
+        with self.assertRaisesMessage(ValueError, 'Empty point is not representable in WKB.'):
+            wkb_w.write_hex(p)
+
+        wkb_w.srid = True
+        for byteorder, hex in enumerate([
+            b'0020000001000010E67FF80000000000007FF8000000000000',
+            b'0101000020E6100000000000000000F87F000000000000F87F',
+        ]):
+            wkb_w.byteorder = byteorder
+            self.assertEqual(wkb_w.write_hex(p), hex)
+            self.assertEqual(GEOSGeometry(wkb_w.write_hex(p)), p)
+            self.assertEqual(wkb_w.write(p), memoryview(binascii.a2b_hex(hex)))
+            self.assertEqual(GEOSGeometry(wkb_w.write(p)), p)
+
+    def test_empty_polygon_wkb(self):
+        p = Polygon(srid=4326)
+        p_no_srid = Polygon()
+        wkb_w = WKBWriter()
+        wkb_w.srid = True
+        for byteorder, hexes in enumerate([
+            (b'000000000300000000', b'0020000003000010E600000000'),
+            (b'010300000000000000', b'0103000020E610000000000000'),
+        ]):
+            wkb_w.byteorder = byteorder
+            for srid, hex in enumerate(hexes):
+                wkb_w.srid = srid
+                self.assertEqual(wkb_w.write_hex(p), hex)
+                self.assertEqual(GEOSGeometry(wkb_w.write_hex(p)), p if srid else p_no_srid)
+                self.assertEqual(wkb_w.write(p), memoryview(binascii.a2b_hex(hex)))
+                self.assertEqual(GEOSGeometry(wkb_w.write(p)), p if srid else p_no_srid)