[Backport 2.x] [Maintenance-2930] Review use of JSON Flattener (#3782)

Backport 87de7e2 from #3674.

---------

Signed-off-by: Prabhas Kurapati <prabhask@berkeley.edu>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Signed-off-by: Darshit Chanpura <dchanp@amazon.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Darshit Chanpura <dchanp@amazon.com>

build.gradle

@@ -575,13 +575,6 @@ dependencies {
     implementation "io.jsonwebtoken:jjwt-api:${jjwt_version}"
     implementation "io.jsonwebtoken:jjwt-impl:${jjwt_version}"
     implementation "io.jsonwebtoken:jjwt-jackson:${jjwt_version}"
-    // JSON flattener
-    implementation ("com.github.wnameless.json:json-base:2.4.3") {
-        exclude group: "org.glassfish", module: "jakarta.json"
-        exclude group: "com.google.code.gson", module: "gson"
-        exclude group: "org.json", module: "json"
-    }
-    implementation 'com.github.wnameless.json:json-flattener:0.16.6'
     // JSON patch
     implementation 'com.flipkart.zjsonpatch:zjsonpatch:0.4.14'
     implementation 'org.apache.commons:commons-collections4:4.4'

src/main/java/org/opensearch/security/compliance/FieldReadCallback.java

@@ -33,11 +33,10 @@
 import org.opensearch.security.auditlog.AuditLog;
 import org.opensearch.security.dlic.rest.support.Utils;
 import org.opensearch.security.support.HeaderHelper;
+import org.opensearch.security.support.JsonFlattener;
 import org.opensearch.security.support.SourceFieldsContext;
 import org.opensearch.security.support.WildcardMatcher;
 
-import com.github.wnameless.json.flattener.JsonFlattener;
-
 //TODO  We need to deal with caching!!
 //Currently we disable caching (and realtime requests) when FLS or DLS is applied
 //Check if we can hook in into the caches
@@ -106,7 +105,7 @@ public void binaryFieldRead(final FieldInfo fieldInfo, byte[] fieldValue) {
                     fieldValue = Utils.jsonMapToByteArray(filteredSource);
                 }
 
-                Map<String, Object> filteredSource = new JsonFlattener(new String(fieldValue, StandardCharsets.UTF_8)).flattenAsMap();
+                Map<String, Object> filteredSource = JsonFlattener.flattenAsMap(new String(fieldValue, StandardCharsets.UTF_8));
                 for (String k : filteredSource.keySet()) {
                     if (!recordField(k, filteredSource.get(k) instanceof String)) {
                         continue;

src/main/java/org/opensearch/security/support/JsonFlattener.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ *
+ */
+
+package org.opensearch.security.support;
+
+import java.io.IOException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+
+import org.opensearch.core.common.Strings;
+import org.opensearch.security.DefaultObjectMapper;
+
+public class JsonFlattener {
+
+    public static Map<String, Object> flattenAsMap(String jsonString) {
+        try {
+            final TypeReference<Map<String, Object>> typeReference = new TypeReference<>() {
+            };
+            final Map<String, Object> jsonMap = DefaultObjectMapper.objectMapper.readValue(jsonString, typeReference);
+            final Map<String, Object> flattenMap = new LinkedHashMap<>();
+            flattenEntries("", jsonMap.entrySet(), flattenMap);
+            return flattenMap;
+        } catch (final IOException ioe) {
+            throw new IllegalArgumentException("Unparseable json", ioe);
+        }
+    }
+
+    private static void flattenEntries(String prefix, final Iterable<Map.Entry<String, Object>> entries, final Map<String, Object> result) {
+        if (!Strings.isNullOrEmpty(prefix)) {
+            prefix += ".";
+        }
+
+        for (final Map.Entry<String, Object> e : entries) {
+            flattenElement(prefix.concat(e.getKey()), e.getValue(), result);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private static void flattenElement(String prefix, final Object source, final Map<String, Object> result) {
+        if (source instanceof Iterable) {
+            flattenCollection(prefix, (Iterable<Object>) source, result);
+        }
+        if (source instanceof Map) {
+            flattenEntries(prefix, ((Map<String, Object>) source).entrySet(), result);
+        }
+        result.put(prefix, source);
+    }
+
+    private static void flattenCollection(String prefix, final Iterable<Object> objects, final Map<String, Object> result) {
+        int counter = 0;
+        for (final Object o : objects) {
+            flattenElement(prefix + "[" + counter + "]", o, result);
+            counter++;
+        }
+    }
+
+}