[FFI] Lightweight json parser/writer

ffi/CMakeLists.txt

@@ -66,6 +66,8 @@ if (TVM_FFI_USE_EXTRA_CXX_API)
   list(APPEND tvm_ffi_objs_sources
     "${CMAKE_CURRENT_SOURCE_DIR}/src/ffi/extra/structural_equal.cc"
     "${CMAKE_CURRENT_SOURCE_DIR}/src/ffi/extra/structural_hash.cc"
+    "${CMAKE_CURRENT_SOURCE_DIR}/src/ffi/extra/json_parser.cc"
+    "${CMAKE_CURRENT_SOURCE_DIR}/src/ffi/extra/json_writer.cc"
   )
 endif()
 

ffi/include/tvm/ffi/extra/json.h

@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/*!
+ * \file tvm/ffi/json/json.h
+ * \brief Minimal lightweight JSON parsing and serialization utilities
+ */
+#ifndef TVM_FFI_EXTRA_JSON_H_
+#define TVM_FFI_EXTRA_JSON_H_
+
+#include <tvm/ffi/any.h>
+#include <tvm/ffi/container/array.h>
+#include <tvm/ffi/container/map.h>
+#include <tvm/ffi/extra/base.h>
+
+namespace tvm {
+namespace ffi {
+namespace json {
+
+/*!
+ * \brief alias Any as json Value.
+ *
+ * To keep things lightweight, we simply reuse the ffi::Any system.
+ */
+using Value = Any;
+
+/*!
+ * \brief alias Map<Any, Any> as json Object.
+ * \note We use Map<Any, Any> instead of Map<String, Any> to avoid
+ *      the overhead of key checking when doing as conversion,
+ *      the check will be performed at runtime when we read each key
+ */
+using Object = ffi::Map<Any, Any>;
+
+/*! \brief alias Array<Any> as json Array. */
+using Array = ffi::Array<Any>;
+
+/*!
+ * \brief Parse a JSON string into an Any value.
+ *
+ * Besides the standard JSON syntax, this function also supports:
+ * - Infinity/NaN as javascript syntax
+ * - int64 integer value
+ *
+ * If error_msg is not nullptr, the error message will be written to it
+ * and no exception will be thrown when parsing fails.
+ *
+ * \param json_str The JSON string to parse.
+ * \param error_msg The output error message, can be nullptr.
+ *
+ * \return The parsed Any value.
+ */
+TVM_FFI_EXTRA_CXX_API json::Value Parse(const String& json_str, String* error_msg = nullptr);
+
+/*!
+ * \brief Serialize an Any value into a JSON string.
+ *
+ * \param value The Any value to serialize.
+ * \param indent The number of spaces to indent the output.
+ *               If not specified, the output will be compact.
+ * \return The output JSON string.
+ */
+TVM_FFI_EXTRA_CXX_API String Stringify(const json::Value& value,
+                                       Optional<int> indent = std::nullopt);
+
+}  // namespace json
+}  // namespace ffi
+}  // namespace tvm
+#endif  // TVM_FFI_EXTRA_JSON_H_