feat(string): add digest length validation for DelEX IFDEQ/IFDNE

- Add 16-character digest validation for IFDEQ/IFDNE options in DelEX command
- Return clear error if digest length is not exactly 16 hexadecimal characters
- Add test case for invalid digest length rejection as requested by reviewer

This commit only modifies DelEX command behavior.

Author: kirito632

src/commands/cmd_string.cc

@@ -118,9 +118,17 @@ class CommandDelEX : public Commander {
     CommandParser parser(args, 2);
     while (parser.Good()) {
       if (parser.EatEqICase("ifdeq")) {
-        option_ = {DelExOption::IFDEQ, GET_OR_RET(parser.TakeStr())};
+        std::string digest = GET_OR_RET(parser.TakeStr());
+        if (digest.size() != 16) {
+          return {Status::RedisParseErr, "ERR digest must be exactly 16 hexadecimal characters"};
+        }
+        option_ = {DelExOption::IFDEQ, std::move(digest)};
       } else if (parser.EatEqICase("ifdne")) {
-        option_ = {DelExOption::IFDNE, GET_OR_RET(parser.TakeStr())};
+        std::string digest = GET_OR_RET(parser.TakeStr());
+        if (digest.size() != 16) {
+          return {Status::RedisParseErr, "ERR digest must be exactly 16 hexadecimal characters"};
+        }
+        option_ = {DelExOption::IFDNE, std::move(digest)};
       } else if (parser.EatEqICase("ifeq")) {
         option_ = {DelExOption::IFEQ, GET_OR_RET(parser.TakeStr())};
       } else if (parser.EatEqICase("ifne")) {

tests/gocase/unit/type/strings/strings_test.go

@@ -349,6 +349,21 @@ func testString(t *testing.T, configs util.KvrocksServerConfigs) {
 		require.Equal(t, "", rdb.Get(ctx, value).Val())
 	})
 
+	t.Run("DelEX IFDEQ and IFDNE reject invalid digest length", func(t *testing.T) {
+		key := "test-string-key-invalid-digest"
+		value := "Hello world"
+
+		require.NoError(t, rdb.Del(ctx, key).Err())
+		require.NoError(t, rdb.Set(ctx, key, value, 0).Err())
+		require.ErrorContains(t, rdb.Do(ctx, "DelEX", key, "ifdeq", "123456789012345").Err(),
+			"exactly 16 hexadecimal characters")
+		require.Equal(t, value, rdb.Get(ctx, key).Val())
+
+		require.ErrorContains(t, rdb.Do(ctx, "DelEX", key, "ifdne", "123456789012345").Err(),
+			"exactly 16 hexadecimal characters")
+		require.Equal(t, value, rdb.Get(ctx, key).Val())
+	})
+
 	t.Run("MGET command", func(t *testing.T) {
 		require.NoError(t, rdb.FlushDB(ctx).Err())
 		require.NoError(t, rdb.Set(ctx, "foo", "BAR", 0).Err())