Fix empty LUA table reply (#3924)

* Fix empty LUA table reply

* processMapKeyValueReply returns List<KeyValue>

* make PROTOCOL_EMPTY_MAP unmodifiable

Author: sazzad16

Diff for: src/main/java/redis/clients/jedis/BuilderFactory.java

@@ -385,7 +385,9 @@ public Object build(Object data) {
 
       if (data instanceof List) {
         final List list = (List) data;
-        if (list.isEmpty()) return Collections.emptyMap();
+        if (list.isEmpty()) {
+          return list == Protocol.PROTOCOL_EMPTY_MAP ? Collections.emptyMap() : Collections.emptyList();
+        }
 
         if (list.get(0) instanceof KeyValue) {
           return ((List<KeyValue>) data).stream()
@@ -397,8 +399,9 @@ public Object build(Object data) {
         }
       } else if (data instanceof byte[]) {
         return STRING.build(data);
+      } else {
+        return data;
       }
-      return data;
     }
   };
 

Diff for: src/main/java/redis/clients/jedis/Protocol.java

@@ -4,6 +4,7 @@
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 
@@ -49,6 +50,8 @@ public final class Protocol {
   public static final byte[] POSITIVE_INFINITY_BYTES = "+inf".getBytes();
   public static final byte[] NEGATIVE_INFINITY_BYTES = "-inf".getBytes();
 
+  static final List<KeyValue> PROTOCOL_EMPTY_MAP = Collections.unmodifiableList(new ArrayList<>(0));
+
   private static final String ASK_PREFIX = "ASK ";
   private static final String MOVED_PREFIX = "MOVED ";
   private static final String CLUSTERDOWN_PREFIX = "CLUSTERDOWN ";
@@ -192,7 +195,6 @@ private static byte[] processBulkReply(final RedisInputStream is) {
   }
 
   private static List<Object> processMultiBulkReply(final RedisInputStream is) {
-  // private static List<Object> processMultiBulkReply(final int num, final RedisInputStream is) {
     final int num = is.readIntCrLf();
     if (num == -1) return null;
     final List<Object> ret = new ArrayList<>(num);
@@ -206,16 +208,20 @@ private static List<Object> processMultiBulkReply(final RedisInputStream is) {
     return ret;
   }
 
-  // private static List<Object> processMultiBulkReply(final RedisInputStream is) {
-  // private static List<Object> processMultiBulkReply(final int num, final RedisInputStream is) {
   private static List<KeyValue> processMapKeyValueReply(final RedisInputStream is) {
     final int num = is.readIntCrLf();
-    if (num == -1) return null;
-    final List<KeyValue> ret = new ArrayList<>(num);
-    for (int i = 0; i < num; i++) {
-      ret.add(new KeyValue(process(is), process(is)));
+    switch (num) {
+      case -1:
+        return null;
+      case 0:
+        return PROTOCOL_EMPTY_MAP;
+      default:
+        final List<KeyValue> ret = new ArrayList<>(num);
+        for (int i = 0; i < num; i++) {
+          ret.add(new KeyValue(process(is), process(is)));
+        }
+        return ret;
     }
-    return ret;
   }
 
   public static Object read(final RedisInputStream is) {

Diff for: src/test/java/redis/clients/jedis/commands/jedis/ScriptingCommandsTest.java

@@ -328,6 +328,12 @@ public void scriptExistsWithBrokenConnection() {
     deadClient.close();
   }
 
+  @Test
+  public void emptyLuaTableReply() {
+    Object reply = jedis.eval("return {}");
+    assertEquals(Collections.emptyList(), reply);
+  }
+
   @Test
   public void functionLoadAndDelete() {
     String engine = "Lua";