SERVER-89322 Change eraseDuplicatePoints() logic to avoid underflows [7.0] (#32646)

GitOrigin-RevId: dd6d19d1cc5d97a73ce32d47ca91f8acf8680b4f

Author: shaargtz

src/mongo/db/geo/geoparser.cpp

@@ -141,7 +141,7 @@ static Status parseArrayOfCoordinates(const BSONElement& elem, vector<S2Point>*
                          << typeName(elem.type()));
     }
     BSONObjIterator it(elem.Obj());
-    // Iterate all coordinates in array
+    // Iterate all coordinates in array.
     while (it.more()) {
         S2Point p;
         Status status = parseGeoJSONCoordinate(it.next(), &p);
@@ -153,11 +153,20 @@ static Status parseArrayOfCoordinates(const BSONElement& elem, vector<S2Point>*
 }
 
 static void eraseDuplicatePoints(vector<S2Point>* vertices) {
-    for (size_t i = 1; i < vertices->size(); ++i) {
-        if ((*vertices)[i - 1] == (*vertices)[i]) {
-            vertices->erase(vertices->begin() + i);
-            // We could have > 2 adjacent identical vertices, and must examine i again.
-            --i;
+    // Duplicates can't exist in a vector of 0 or 1 elements, and we want to be careful about
+    // possible underflow of size - 1 in the next block.
+    if (vertices->size() < 2) {
+        return;
+    }
+
+    size_t i = 0;
+    while (i < vertices->size() - 1) {
+        if ((*vertices)[i] == (*vertices)[i + 1]) {
+            vertices->erase(vertices->begin() + i + 1);
+            // We could have > 2 adjacent identical vertices, and must examine i again, so we don't
+            // increment the iterator.
+        } else {
+            ++i;
         }
     }
 }

src/mongo/db/geo/geoparser_test.cpp

@@ -125,6 +125,8 @@ TEST(GeoParser, parseGeoJSONLine) {
         fromjson("{'type':'LineString', 'coordinates':[[1,2, 3], [3,4, 5], [5,6]]}"),
         false,
         &polyline));
+    ASSERT_NOT_OK(GeoParser::parseGeoJSONLine(
+        fromjson("{'type':'LineString', 'coordinates':[[1,2], [1,2]]}"), false, &polyline));
 }
 
 TEST(GeoParser, parseGeoJSONPolygon) {
@@ -220,6 +222,34 @@ TEST(GeoParser, parseGeoJSONPolygon) {
         &polygonBad));
 }
 
+TEST(GeoParser, parseGeoJSONPolygonStrictSphere) {
+    string crs = "crs:{ type: 'name', properties:{name:'" + CRS_STRICT_WINDING + "'}}";
+    PolygonWithCRS polygon;
+    BSONObj bigSimplePolygon = fromjson(
+        "{'type':'Polygon', 'coordinates':[ "
+        "[[0,0],[5,0],[5,5],[0,5],[0,0]]], " +
+        crs + "}");
+    ASSERT_OK(GeoParser::parseGeoJSONPolygon(bigSimplePolygon, false, &polygon));
+
+    BSONObj bigSimplePolygonWithValidDuplicates = fromjson(
+        "{'type':'Polygon', 'coordinates':[ "
+        "[[0,0],[5,0],[5,5],[5,5],[0,5],[0,0]]], " +
+        crs + "}");
+    ASSERT_OK(GeoParser::parseGeoJSONPolygon(bigSimplePolygonWithValidDuplicates, false, &polygon));
+
+    BSONObj bigSimplePolygonWithInvalidDuplicates = fromjson(
+        "{'type':'Polygon', 'coordinates':[ "
+        "[[0,0],[5,0],[5,0],[0,0],[0,0]]], " +
+        crs + "}");
+    ASSERT_NOT_OK(
+        GeoParser::parseGeoJSONPolygon(bigSimplePolygonWithInvalidDuplicates, false, &polygon));
+
+    BSONObj bigSimplePolygonWithFewPoints = fromjson(
+        "{'type':'Polygon', 'coordinates':[ "
+        "[[0,0]]], " +
+        crs + "}");
+    ASSERT_NOT_OK(GeoParser::parseGeoJSONPolygon(bigSimplePolygonWithFewPoints, false, &polygon));
+}
 
 TEST(GeoParser, parseGeoJSONCRS) {
     string goodCRS1 = "crs:{ type: 'name', properties:{name:'EPSG:4326'}}";