Fix segfault in cellsToMultiPolygon due to reading invalid pointers (#129)

* Fix segfault in cellsToMultiPolygon due to reading invalid pointers

* Add PR number

Author: isaacbrodsky

CHANGELOG.md

@@ -7,6 +7,9 @@ file [H3Core.java](./src/main/java/com/uber/h3core/H3Core.java), and support
 for the Linux x64 and Darwin x64 platforms.
 
 ## Unreleased Changes
+## Fixed
+- Fixed a potential segfault in `cellsToMultiPolygon` on error. (#129)
+
 ## [4.1.1] - 2023-02-03
 The changelog for this release is the same as v4.1.0. The release was run again due to an issue with the release process.
 

pom.xml

@@ -168,7 +168,7 @@
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
-            <version>4.13.1</version>
+            <version>4.13.2</version>
             <scope>test</scope>
         </dependency>
         <dependency>

src/main/c/h3-java/src/jniapi.c

@@ -699,17 +699,18 @@ Java_com_uber_h3core_NativeMethods_cellsToLinkedMultiPolygon(JNIEnv *env,
     if (h3Elements != NULL) {
         H3Error err = cellsToLinkedMultiPolygon(h3Elements, numH3, &polygon);
 
-        // Parse the output now
-        LinkedGeoPolygon *currentPolygon = &polygon;
+        if (err) {
+            (**env).ReleaseLongArrayElements(env, h3, h3Elements, 0);
+            ThrowH3Exception(env, err);
+        } else {
+            // Parse the output now
+            LinkedGeoPolygon *currentPolygon = &polygon;
 
-        ConvertLinkedGeoPolygonToManaged(env, currentPolygon, results);
+            ConvertLinkedGeoPolygonToManaged(env, currentPolygon, results);
 
-        destroyLinkedMultiPolygon(&polygon);
+            destroyLinkedMultiPolygon(&polygon);
 
-        (**env).ReleaseLongArrayElements(env, h3, h3Elements, 0);
-
-        if (err) {
-            ThrowH3Exception(env, err);
+            (**env).ReleaseLongArrayElements(env, h3, h3Elements, 0);
         }
     } else {
         ThrowOutOfMemoryError(env);

src/test/java/com/uber/h3core/TestRegion.java

@@ -20,6 +20,7 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
+import com.uber.h3core.exceptions.H3Exception;
 import com.uber.h3core.util.LatLng;
 import java.util.ArrayList;
 import java.util.List;
@@ -270,4 +271,117 @@ public void testH3SetToMultiPolygonLarge() {
       assertEquals(6, multiBounds.get(i).get(0).size());
     }
   }
+
+  @Test(expected = H3Exception.class)
+  public void testH3SetToMultiPolygonIssue753() {
+    // Test case reported in https://github.com/uber/h3/issues/753
+    // Ensure it does not crash
+    List<Long> cells =
+        ImmutableList.of(
+            617683643010646015L,
+            617683648070287359L,
+            617683642951663615L,
+            617683648070287359L,
+            617683648070549503L,
+            617683643014840319L,
+            617683643013791743L,
+            617683642951663615L,
+            617683642951663615L,
+            617683648065044479L,
+            617683648070549503L,
+            617683643010383871L,
+            617683643010646015L,
+            617683643013791743L,
+            617683643008024575L,
+            617683643014840319L,
+            617683643010383871L,
+            617683642941177855L,
+            617683642941177855L,
+            617683642941439999L,
+            617683642951663615L,
+            617683642950615039L,
+            617683642950877183L,
+            617683648065044479L,
+            617683648070549503L,
+            617683648057180159L,
+            617683648065044479L,
+            617683648064520191L,
+            617683643013791743L,
+            617683643014316031L,
+            617683643008548863L,
+            617683643007238143L,
+            617683643008024575L,
+            617683643010383871L,
+            617683642953498623L,
+            617683642941177855L,
+            617683643014316031L,
+            617683642953760767L,
+            617683642941439999L,
+            617683642951139327L,
+            617683642950615039L,
+            617683642951663615L,
+            617683648065044479L,
+            617683642950877183L,
+            617683648064258047L,
+            617683648063471615L,
+            617683648066093055L,
+            617683648057180159L,
+            617683648064520191L,
+            617683648057180159L,
+            617683648070549503L,
+            617683648066093055L,
+            617683643019296767L,
+            617683643008548863L,
+            617683643010383871L,
+            617683643018510335L,
+            617683643017723903L,
+            617683642953760767L,
+            617683642954285055L,
+            617683642953236479L,
+            617683642953498623L,
+            617683642953498623L,
+            617683642940129279L,
+            617683642941177855L,
+            617683642950877183L,
+            617683644212576255L,
+            617683644211003391L,
+            617683644212314111L,
+            617683648064258047L,
+            617683648057180159L,
+            617683648057442303L,
+            617683648068190207L,
+            617683648057180159L,
+            617683648064520191L,
+            617683648064782335L,
+            617683648060850175L,
+            617683648057442303L,
+            617683648070811647L,
+            617683648071335935L,
+            617683648070287359L,
+            617683648070549503L,
+            617683648131366911L,
+            617683648070811647L,
+            617683648066093055L,
+            617683648067141631L,
+            617683642944585727L,
+            617683642947469311L,
+            617683642940915711L,
+            617683642940129279L,
+            617683642953498623L,
+            617683642945372159L,
+            617683642944323583L,
+            617683642944585727L,
+            617683648065568767L,
+            617683648066093055L,
+            617683648065830911L,
+            617683648065830911L,
+            617683648068190207L,
+            617683648067665919L,
+            617683648028344319L,
+            617683648065830911L,
+            617683648067665919L,
+            617683648068976639L,
+            617683648028606463L);
+    h3.cellsToMultiPolygon(cells, true);
+  }
 }