TopologyPreservingSimplifier: Avoid stack overflow on degenerate input

Fixes #1070
libgeos · Jun 19, 2024 · a02617f · a02617f
1 parent f03a3f3
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diff --git a/src/simplify/TaggedLineStringSimplifier.cpp b/src/simplify/TaggedLineStringSimplifier.cpp
@@ -144,6 +144,18 @@ TaggedLineStringSimplifier::simplifySection(std::size_t i,
               << std::endl;
 #endif
 
+    if (distance < 0) {
+        // negative distance indicates that we could not compute distance to the
+        // farthest point, probably because of infinite or large-magnitude coordinates.
+        // avoid trying to simplify this section.
+        for (std::size_t k = i; k < j; k++) {
+            auto newSeg = std::make_unique<TaggedLineSegment>(*(line->getSegment(k)));
+            line->addToResult(std::move(newSeg));
+        }
+
+        return;
+    }
+
     // flattening must be less than distanceTolerance
     if(distance > distanceTolerance) {
         isValidToSimplify = false;

diff --git a/tests/unit/simplify/TopologyPreservingSimplifierTest.cpp b/tests/unit/simplify/TopologyPreservingSimplifierTest.cpp
@@ -430,5 +430,17 @@ void object::test<33>()
         "POLYGON ((-222618.41756525903 6299886.966175825, -222510 6300300, -221720.85158014414 6300132.680680807, -222448.77936063593 6299647.669870703, -222618.41756525903 6299886.966175825), (-222467.0202338936 6299970.185860572, -222456.57057590774 6299931.950053182, -222490.56062790897 6299837.359974515, -222415.1394852571 6299926.6972160805, -222421.19226152284 6299963.389132584, -222467.0202338936 6299970.185860572))");
 }
 
+// https://github.com/libgeos/geos/issues/1070
+template<>
+template<>
+void object::test<34>()
+{
+    auto input = wktreader.read("MULTILINESTRING((0	0, 1 0001211111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111, 1 00015111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111,	1 0001511111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111, 1 0, 10 01, 0 0))");
+
+    auto simplified = TopologyPreservingSimplifier::simplify(input.get(), 2.0);
+
+    ensure(simplified != nullptr); // no crash
+}
+
 
 } // namespace tut