implementing decoder interface

Author: andreagilardoni

src/cbor/CborDecoder.cpp

@@ -0,0 +1,78 @@
+/*
+    This file is part of the Arduino_CloudUtils library.
+
+    Copyright (c) 2024 Arduino SA
+
+    This Source Code Form is subject to the terms of the Mozilla Public
+    License, v. 2.0. If a copy of the MPL was not distributed with this
+    file, You can obtain one at http://mozilla.org/MPL/2.0/.
+*/
+#include "CborDecoder.h"
+
+static CBORMessageDecoderClass* singleton = nullptr;
+CBORMessageDecoderClass& CBORMessageDecoder = CBORMessageDecoderClass::getInstance();
+
+Decoder::Status CBORMessageDecoderClass::decode(Message* msg, const uint8_t* const buf, size_t &len) { // TODO do we need to propagate the maximum length?
+  // prepare cbor structure
+  CborValue iter;
+  CborTag tag;
+  CborParser parser;
+
+  if (cbor_parser_init(buf, len, 0, &parser, &iter) != CborNoError) {
+    return Decoder::Status::Error;
+  }
+
+  if (iter.type != CborTagType) {
+    return Decoder::Status::Error;
+  }
+
+  if (cbor_value_get_tag(&iter, &tag) != CborNoError) {
+    return Decoder::Status::Error;
+  }
+
+  if (cbor_value_advance(&iter) != CborNoError) {
+    return Decoder::Status::Error;
+  }
+
+  auto decoder_it = decoders.find(tag);
+
+  // check if message.id exists on the decoders list or return error
+  if(decoder_it == decoders.end()) {
+    return Decoder::Status::Error;
+  }
+
+  // encode the message
+  if(decoder_it->second->_decode(&iter, msg) == Decoder::Status::Error) {
+    return Decoder::Status::Error;
+  }
+
+  return Decoder::Status::Complete;
+}
+
+CBORMessageDecoderClass& CBORMessageDecoderClass::getInstance() {
+  if(singleton == nullptr) {
+    singleton = new CBORMessageDecoderClass();
+  }
+  return *singleton;
+}
+
+CBORMessageDecoderInterface::CBORMessageDecoderInterface(const CBORTag tag, const MessageId id)
+: tag(tag), id(id) {
+  // call singleton/global variable and insert this encoder
+  CBORMessageDecoderClass::getInstance().append(tag, this);
+}
+
+Decoder::Status CBORMessageDecoderInterface::_decode(CborValue* iter, Message *msg) {
+  CborValue array_iter;
+  msg->id = this->id;
+
+  if (cbor_value_get_type(iter) != CborArrayType) {
+    return Decoder::Status::Error;
+  }
+
+  if (cbor_value_enter_container(iter, &array_iter) != CborNoError) {
+    return Decoder::Status::Error;
+  }
+
+  return decode(&array_iter, msg);
+}

src/cbor/CborDecoder.h

@@ -0,0 +1,58 @@
+/*
+    This file is part of the Arduino_CloudUtils library.
+
+    Copyright (c) 2024 Arduino SA
+
+    This Source Code Form is subject to the terms of the Mozilla Public
+    License, v. 2.0. If a copy of the MPL was not distributed with this
+    file, You can obtain one at http://mozilla.org/MPL/2.0/.
+*/
+#pragma once
+
+#include <map>
+#include "../interfaces/Decoder.h"
+#include "CBOR.h"
+#include "../interfaces/message.h"
+#include "./tinycbor/cbor-lib.h"
+
+class CBORMessageDecoderClass;
+
+// TODO find a better name
+// TODO maybe a template<CBORTag tag, MessageId id> ?
+// TODO maybe template<resultStruct> that is also the parameter of encode
+// TODO in order to make this more extensible we should not pass Message* as a parameter, templated function may be better (or void*)
+// providing both id and tag gives the ability to convert and avoid using a conversion function
+class CBORMessageDecoderInterface {
+public:
+  CBORMessageDecoderInterface(const CBORTag tag, const MessageId id);
+  virtual ~CBORMessageDecoderInterface() {}
+
+protected:
+  virtual Decoder::Status decode(CborValue* iter, Message *msg) = 0;
+
+private:
+  const CBORTag tag;
+  const MessageId id;
+
+  friend CBORMessageDecoderClass;
+
+  // wrapper for encode function that for the time being only writes the tag in the buffer
+  Decoder::Status _decode(CborValue* iter, Message *msg);
+};
+
+// TODO make a private constructor?
+class CBORMessageDecoderClass: public Decoder {
+public:
+  CBORMessageDecoderClass() {}
+  static CBORMessageDecoderClass& getInstance();
+
+  void append(CBORTag id, CBORMessageDecoderInterface* encoder) {
+    decoders[id] = encoder;
+  }
+
+  Decoder::Status decode(Message* msg, const uint8_t* const buf, size_t &len);
+private:
+  std::map<CBORTag, CBORMessageDecoderInterface*> decoders;
+};
+
+extern CBORMessageDecoderClass& CBORMessageDecoder;