fix(sentry): Unwind MapObjectReader failures fully

Recover MapObjectReader values back to their stack checkpoint so
partially consumed nested objects do not leave child entries or end
sentinels behind.

This keeps later values readable after a deserializer fails mid-object
and adds regression coverage for list, map, and map-of-lists paths that
partially enter nested values before throwing.

Refs GH-5278
Co-Authored-By: Claude <noreply@anthropic.com>

Author: adinauer

sentry/src/main/java/io/sentry/util/MapObjectReader.java

@@ -31,15 +31,12 @@ public MapObjectReader(final Map<String, Object> root) {
   @Override
   public void nextUnknown(
       final @NotNull ILogger logger, final Map<String, Object> unknown, final String name) {
+    final int stackSizeBefore = stack.size();
     try {
       unknown.put(name, nextObjectOrNull());
     } catch (Exception exception) {
       logger.log(SentryLevel.ERROR, exception, "Error deserializing unknown key: %s", name);
-      try {
-        skipValue();
-      } catch (Exception ignored) {
-        // stream is unrecoverable
-      }
+      recoverValue(stackSizeBefore);
     }
   }
 
@@ -57,11 +54,12 @@ public <T> List<T> nextListOrNull(
       List<T> list = new ArrayList<>();
       if (hasNext()) {
         do {
+          final int stackSizeBefore = stack.size();
           try {
             list.add(deserializer.deserialize(this, logger));
           } catch (Exception e) {
             logger.log(SentryLevel.WARNING, "Failed to deserialize object in list.", e);
-            skipValue();
+            recoverValue(stackSizeBefore);
           }
         } while (peek() == JsonToken.BEGIN_OBJECT);
       }
@@ -87,11 +85,12 @@ public <T> Map<String, T> nextMapOrNull(
       if (hasNext()) {
         do {
           final String key = nextName();
+          final int stackSizeBefore = stack.size();
           try {
             map.put(key, deserializer.deserialize(this, logger));
           } catch (Exception e) {
             logger.log(SentryLevel.WARNING, "Failed to deserialize object in map.", e);
-            skipValue();
+            recoverValue(stackSizeBefore);
           }
         } while (peek() == JsonToken.BEGIN_OBJECT || peek() == JsonToken.NAME);
       }
@@ -116,14 +115,15 @@ public <T> Map<String, T> nextMapOrNull(
       if (hasNext()) {
         do {
           final @NotNull String key = nextName();
+          final int stackSizeBefore = stack.size();
           try {
             final @Nullable List<T> list = nextListOrNull(logger, deserializer);
             if (list != null) {
               result.put(key, list);
             }
           } catch (Exception e) {
             logger.log(SentryLevel.WARNING, "Failed to deserialize list in map.", e);
-            skipValue();
+            recoverValue(stackSizeBefore);
           }
         } while (peek() == JsonToken.BEGIN_OBJECT || peek() == JsonToken.NAME);
       }
@@ -397,6 +397,12 @@ public void skipValue() throws IOException {
     }
   }
 
+  private void recoverValue(final int stackSizeBefore) {
+    while (!stack.isEmpty() && stack.size() >= stackSizeBefore) {
+      stack.removeLast();
+    }
+  }
+
   @SuppressWarnings("TypeParameterUnusedInFormals")
   @Nullable
   private <T> T nextValueOrNull() throws IOException {

sentry/src/test/java/io/sentry/util/MapObjectReaderTest.kt

@@ -49,6 +49,25 @@ class MapObjectReaderTest {
 
   private fun serializableValue(value: String): Map<String, Any> = linkedMapOf("test" to value)
 
+  private fun partialSerializableValue(kind: String, value: String): Map<String, Any> =
+    linkedMapOf("test" to value, "kind" to kind)
+
+  private val partiallyFailingDeserializer =
+    JsonDeserializer<BasicSerializable> { reader, _ ->
+      val basicSerializable = BasicSerializable()
+      reader.beginObject()
+      if (reader.nextName() == "kind") {
+        if (reader.nextString() == "fail") {
+          throw IllegalStateException("intentional")
+        }
+      }
+      if (reader.nextName() == "test") {
+        basicSerializable.test = reader.nextString()
+      }
+      reader.endObject()
+      basicSerializable
+    }
+
   @Test
   fun `deserializes data correctly`() {
     val data = mutableMapOf<String, Any>()
@@ -244,4 +263,46 @@ class MapObjectReaderTest {
 
     assertEquals(mapOf("good" to listOf(BasicSerializable("two"))), actual)
   }
+
+  @Test(timeout = 1000L)
+  fun `nextListOrNull keeps elements after a partially consumed failing element`() {
+    val actual =
+      getValuesReader(
+          listOf(partialSerializableValue("fail", "bad"), partialSerializableValue("ok", "two"))
+        )
+        .nextListOrNull(logger, partiallyFailingDeserializer)
+
+    assertEquals(listOf(BasicSerializable("two")), actual)
+  }
+
+  @Test(timeout = 1000L)
+  fun `nextMapOrNull keeps values after a partially consumed failing value`() {
+    val actual =
+      getValuesReader(
+          linkedMapOf(
+            "bad" to partialSerializableValue("fail", "bad"),
+            "good" to partialSerializableValue("ok", "two"),
+          )
+        )
+        .nextMapOrNull(logger, partiallyFailingDeserializer)
+
+    assertEquals(mapOf("good" to BasicSerializable("two")), actual)
+  }
+
+  @Test(timeout = 1000L)
+  fun `nextMapOfListOrNull keeps values after a partially consumed failing element`() {
+    val actual =
+      getValuesReader(
+          linkedMapOf(
+            "bad" to listOf(partialSerializableValue("fail", "bad")),
+            "good" to listOf(partialSerializableValue("ok", "two")),
+          )
+        )
+        .nextMapOfListOrNull(logger, partiallyFailingDeserializer)
+
+    assertEquals(
+      mapOf("bad" to emptyList<BasicSerializable>(), "good" to listOf(BasicSerializable("two"))),
+      actual,
+    )
+  }
 }