BE: Messages: Implement null filtering for CEL (#1050)

Co-authored-by: German Osin <german.osin@gmail.com>

Author: Haarolean

api/src/main/java/io/kafbat/ui/emitter/MessageFilters.java

@@ -7,6 +7,7 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.collect.ImmutableCollection;
 import com.google.common.collect.ImmutableSet;
+import com.google.protobuf.NullValue;
 import dev.cel.common.CelAbstractSyntaxTree;
 import dev.cel.common.CelOptions;
 import dev.cel.common.CelValidationException;
@@ -26,6 +27,7 @@
 import io.kafbat.ui.exception.CelException;
 import io.kafbat.ui.model.TopicMessageDTO;
 import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
@@ -38,11 +40,13 @@
 @Slf4j
 @UtilityClass
 public class MessageFilters {
+
   private static final String CEL_RECORD_VAR_NAME = "record";
   private static final String CEL_RECORD_TYPE_NAME = TopicMessageDTO.class.getSimpleName();
 
   private static final CelCompiler CEL_COMPILER = createCompiler();
   private static final CelRuntime CEL_RUNTIME = createRuntime();
+  private static final Object CELL_NULL_VALUE = NullValue.NULL_VALUE;
 
   private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
 
@@ -188,10 +192,34 @@ private static Object parseToJsonOrReturnAsIs(@Nullable String str) {
     }
 
     try {
-      return OBJECT_MAPPER.readValue(str, new TypeReference<Map<String, Object>>() {
-      });
+      //@formatter:off
+      var map = OBJECT_MAPPER.readValue(str, new TypeReference<Map<String, Object>>() {});
+      //@formatter:on
+      return replaceCelNulls(map);
     } catch (JsonProcessingException e) {
       return str;
     }
   }
+
+  @SuppressWarnings("unchecked")
+  private static Map<String, Object> replaceCelNulls(Map<String, Object> map) {
+    var result = new LinkedHashMap<String, Object>();
+
+    for (var entry : map.entrySet()) {
+      String key = entry.getKey();
+      Object value = entry.getValue();
+
+      if (value == null) {
+        result.put(key, CELL_NULL_VALUE);
+      } else if (value instanceof Map<?, ?>) {
+        var inner = (Map<String, Object>) value;
+        result.put(key, replaceCelNulls(inner));
+      } else {
+        result.put(key, value);
+      }
+    }
+
+    return result;
+  }
+
 }

api/src/test/java/io/kafbat/ui/emitter/MessageFiltersTest.java

@@ -201,6 +201,18 @@ void filterSpeedIsAtLeast5kPerSec() {
       assertThat(took).isLessThan(1000);
       assertThat(matched).isPositive();
     }
+
+    @Test
+    void nullFiltering() {
+      String msg = "{ \"field\": { \"inner\": null } }";
+
+      var f = celScriptFilter("record.value.field.inner == null");
+      assertTrue(f.test(msg().content(msg)));
+
+      f = celScriptFilter("record.value.field.inner != null");
+      assertFalse(f.test(msg().content(msg)));
+    }
+
   }
 
   @Test