Fix metadata parsing for JSON object strings

src/main/java/com/chargebee/v4/internal/JsonUtil.java

@@ -5,6 +5,7 @@
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
 import com.google.gson.JsonParser;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.JsonSerializer;
@@ -135,12 +136,19 @@ public static Timestamp getTimestamp(JsonObject obj, String key) {
         return epochSeconds != null ? new Timestamp(epochSeconds * 1000) : null;
     }
 
-    /** Returns a nested JsonObject for the given key, or null. */
+    /** Returns a nested or string-encoded JsonObject for the given key, or null. */
     public static JsonObject getJsonObject(JsonObject obj, String key) {
         if (obj == null || key == null) return null;
         JsonElement elem = obj.get(key);
-        if (elem == null || elem.isJsonNull() || !elem.isJsonObject()) return null;
-        return elem.getAsJsonObject();
+        if (elem == null || elem.isJsonNull()) return null;
+        if (elem.isJsonPrimitive() && elem.getAsJsonPrimitive().isString()) {
+            try {
+                elem = JsonParser.parseString(elem.getAsString());
+            } catch (JsonParseException e) {
+                return null;
+            }
+        }
+        return elem.isJsonObject() ? elem.getAsJsonObject() : null;
     }
 
     /** Returns a nested JsonArray for the given key, or null. */

src/test/java/com/chargebee/v4/internal/JsonUtilTest.java

@@ -3,6 +3,8 @@
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
 import org.junit.jupiter.api.*;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 import java.math.BigDecimal;
 import java.sql.Timestamp;
@@ -286,6 +288,28 @@ class GetObjectTests {
             assertNull(JsonUtil.getJsonObject(obj, "name"));
         }
 
+        @Test void getJsonObjectDecodesString() {
+            JsonObject root = new JsonObject();
+            root.addProperty("metadata", "{\"reason\":\"test-promo-claim\"}");
+            JsonObject metadata = JsonUtil.getJsonObject(root, "metadata");
+            assertNotNull(metadata);
+            assertEquals("test-promo-claim", metadata.get("reason").getAsString());
+        }
+
+        @Test void getJsonObjectDecodesEmptyObjectString() {
+            JsonObject root = new JsonObject();
+            root.addProperty("metadata", "{}");
+            assertEquals(new JsonObject(), JsonUtil.getJsonObject(root, "metadata"));
+        }
+
+        @ParameterizedTest
+        @ValueSource(strings = {"", " ", "not json", "{", "{\"reason\":", "[]", "[{}]", "null", "true", "42", "\"text\""})
+        void getJsonObjectRejectsInvalidOrNonObjectStrings(String value) {
+            JsonObject root = new JsonObject();
+            root.addProperty("metadata", value);
+            assertNull(JsonUtil.getJsonObject(root, "metadata"));
+        }
+
         @Test void getObjectReturnsJsonString() {
             JsonObject root = JsonUtil.parse("{\"meta\": {\"key\": \"val\"}}");
             String meta = JsonUtil.getObject(root, "meta");

src/test/java/com/chargebee/v4/internal/MetadataParserTest.java

@@ -0,0 +1,107 @@
+package com.chargebee.v4.internal;
+
+import com.chargebee.v4.client.ChargebeeClient;
+import com.chargebee.v4.models.grantBlock.GrantBlock;
+import com.chargebee.v4.models.item.Item;
+import com.chargebee.v4.models.itemPrice.ItemPrice;
+import com.chargebee.v4.models.ledgerOperation.params.LedgerOperationAllocateParams;
+import com.chargebee.v4.models.ledgerOperation.responses.LedgerOperationAllocateResponse;
+import com.google.gson.JsonObject;
+import com.sun.net.httpserver.HttpServer;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class MetadataParserTest {
+
+    private static final Map<String, Object> METADATA = Map.of(
+            "grantor", "local-test",
+            "grantor_type", "test_operator",
+            "reason", "test-promo-claim",
+            "nested", Map.of("eligible", true, "amount", 25L),
+            "labels", Arrays.asList("café", null),
+            "quoted", "a \"quote\"\\path\nline",
+            "opaque", "{\"keep\":\"string\"}");
+
+    @ParameterizedTest
+    @CsvSource({"false,false", "false,true", "true,false", "true,true"})
+    void allocatePreservesMetadataOverLocalHttp(boolean stringEncoded, boolean async) throws Exception {
+        JsonObject block = metadataModel(stringEncoded);
+        block.addProperty("id", "local-grant");
+        block.addProperty("grant_source", "promotional");
+        String body = "{\"grant_blocks\":[" + block + "]}";
+        byte[] responseBytes = body.getBytes(StandardCharsets.UTF_8);
+        AtomicReference<String> requestBody = new AtomicReference<>();
+        AtomicReference<String> requestMethod = new AtomicReference<>();
+        AtomicReference<String> requestPath = new AtomicReference<>();
+        HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
+        server.createContext("/api/v2/ledger_operations/allocate", exchange -> {
+            requestBody.set(new String(exchange.getRequestBody().readAllBytes(), StandardCharsets.UTF_8));
+            requestMethod.set(exchange.getRequestMethod());
+            requestPath.set(exchange.getRequestURI().getPath());
+            exchange.getResponseHeaders().set("Content-Type", "application/json; charset=utf-8");
+            exchange.sendResponseHeaders(200, responseBytes.length);
+            exchange.getResponseBody().write(responseBytes);
+            exchange.close();
+        });
+        server.start();
+        try (ChargebeeClient client = ChargebeeClient.builder("local-test-key", "local-test")
+                .endpoint("http://127.0.0.1:" + server.getAddress().getPort() + "/api/v2")
+                .build()) {
+            LedgerOperationAllocateParams params = LedgerOperationAllocateParams.builder()
+                    .subscriptionId("local-subscription").unitId("local-unit")
+                    .id("local-allocation").amount("25").metadata(METADATA).build();
+            LedgerOperationAllocateResponse response = async
+                    ? client.ledgerOperations().allocateAsync(params).get(10, TimeUnit.SECONDS)
+                    : client.ledgerOperations().allocate(params);
+
+            assertEquals("POST", requestMethod.get());
+            assertEquals("/api/v2/ledger_operations/allocate", requestPath.get());
+            assertEquals(JsonUtil.parse(JsonUtil.toJson(METADATA)),
+                    JsonUtil.parse(requestBody.get()).get("metadata"));
+            assertEquals(1, response.getGrantBlocks().size());
+            GrantBlock grant = response.getGrantBlocks().get(0);
+            assertEquals("local-grant", grant.getId());
+            assertEquals("test-promo-claim", grant.getMetadata().get("reason"));
+            assertEquals(METADATA, grant.getMetadata());
+        } finally {
+            server.stop(0);
+        }
+    }
+
+    @ParameterizedTest
+    @ValueSource(booleans = {false, true})
+    void itemAndItemPricePreserveMetadata(boolean stringEncoded) {
+        JsonObject model = metadataModel(stringEncoded);
+        assertEquals(METADATA, Item.fromJson(model).getMetadata());
+        assertEquals(METADATA, ItemPrice.fromJson(model).getMetadata());
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"{}", "{\"metadata\":null}", "{\"metadata\":{}}", "{\"metadata\":\"{}\"}",
+            "{\"metadata\":\"{\"}", "{\"metadata\":[]}", "{\"metadata\":42}", "{\"metadata\":true}"})
+    void absentOrInvalidMetadataRemainsEmpty(String json) {
+        assertTrue(GrantBlock.fromJson(json).getMetadata().isEmpty());
+        assertTrue(Item.fromJson(json).getMetadata().isEmpty());
+        assertTrue(ItemPrice.fromJson(json).getMetadata().isEmpty());
+    }
+
+    private static JsonObject metadataModel(boolean stringEncoded) {
+        JsonObject model = new JsonObject();
+        String json = JsonUtil.toJson(METADATA);
+        if (stringEncoded) {
+            model.addProperty("metadata", json);
+        } else {
+            model.add("metadata", JsonUtil.parse(json));
+        }
+        return model;
+    }
+}