implementing encoder interface

Author: andreagilardoni

src/cbor/CborEncoder.cpp

@@ -0,0 +1,80 @@
+/*
+    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 "CborEncoder.h"
+#include <algorithm>
+
+Encoder::Status CBORMessageEncoderSingleton::encode(Message* message, uint8_t * data, size_t& len) { // TODO do we need to propagate the maximum length?
+  // prepare cbor structure
+  CborEncoder encoder;
+
+  cbor_encoder_init(&encoder, data, len, 0);
+
+  auto encoder_it = encoders.begin();
+
+  for(; encoder_it != encoders.end(); encoder_it++) {
+    if(encoder_it->first == message->id) {
+      break;
+    }
+  }
+
+  // check if message.id exists on the encoders list or return error
+  if(encoder_it == encoders.end()) {
+    return Encoder::Status::Error;
+  }
+
+  // encode the message
+  if(encoder_it->second->_encode(&encoder, message) == Encoder::Status::Error) {
+    return Encoder::Status::Error;
+  }
+
+  len = cbor_encoder_get_buffer_size(&encoder, data);
+
+  return Encoder::Status::Complete;
+}
+
+CBORMessageEncoderSingleton& CBORMessageEncoderSingleton::getInstance() {
+  static CBORMessageEncoderSingleton singleton;
+
+  return singleton;
+}
+
+void CBORMessageEncoderSingleton::append(MessageId id, CBORMessageEncoderInterface* encoder) {
+  auto encoder_it = encoders.begin();
+
+  for(; encoder_it != encoders.end(); encoder_it++) {
+    if(encoder_it->first == id) {
+      return;
+    }
+  }
+
+  encoders.push_back(
+    std::make_pair(id, encoder)
+  );
+}
+
+CBORMessageEncoderInterface::CBORMessageEncoderInterface(const CBORTag tag, const MessageId id)
+: tag(tag), id(id) {
+  // call singleton/global variable and insert this encoder
+  CBORMessageEncoderSingleton::getInstance().append(id, this);
+}
+
+Encoder::Status CBORMessageEncoderInterface::_encode(CborEncoder* encoder, Message *msg) {
+  // this must always be true, it could mean that there are issues in the map of encoders
+  assert(msg->id == id);
+
+  if (tag == cbor::tag::CBORUnknownCmdTag16b ||
+      tag == cbor::tag::CBORUnknownCmdTag32b ||
+      tag == cbor::tag::CBORUnknownCmdTag64b ||
+      cbor_encode_tag(encoder, tag) != CborNoError) {
+    return Encoder::Status::Error;
+  }
+
+  return this->encode(encoder, msg);
+}

src/cbor/CborEncoder.h

@@ -0,0 +1,132 @@
+/*
+    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 <vector>
+#include "../interfaces/Encoder.h"
+#include "CBOR.h"
+#include "../interfaces/message.h"
+#include "./tinycbor/cbor-lib.h"
+
+// forward declaration
+class CBORMessageEncoderSingleton;
+
+/*
+ * This library collects the interfaces used to encode Messages. Messages are C structs
+ * that are identified by a uint32 id after which they can contain anything.
+ * The objective of this library is to be modular and extensible in other libraries.
+ *
+ * In order to do so one have to extend the class `CBORMessageEncoderInterface`,
+ * provide the associated CBORTag and MessageId and provide a way to encode the message
+ * specific data. MessageId must be univocal across all EncoderInterfaces instantiated.
+ * The class implemented must be instantiated somewhere (using extern may be helpful)
+ * and that is enough to have it included in the encode process.
+ *
+ * In order to encode a message one can instantiate `CBORMessageEncoder` and
+ * call the encode function.
+ */
+
+/**
+ * CBORMessageEncoderInterface class is an abstract class one has to implement
+ * in order to provide the instructions needed to encode a buffer contasining
+ * a message specific data.
+ */
+class CBORMessageEncoderInterface {
+public:
+
+  /**
+   * Constructor that initializes the CBORMessageEncoderInterface by providing the associated
+   * CBORTag and MessageId. The constructor also appends the object into CBORMessageEncoderSingleton
+   * allowing it to be used in CBORMessageEncoderSingleton::encode
+   *
+   * @param tag the cbor tag the message is associated with
+   * @param id  the message id the message is associated with
+   */
+  CBORMessageEncoderInterface(const CBORTag tag, const MessageId id);
+  virtual ~CBORMessageEncoderInterface() {}
+
+protected:
+
+  /**
+   * Abstract encode function one must implement to encode a Message into a provided buffer
+   *
+   * @param encoder tinycbor encoder struct
+   * @param msg     The message from which data must be extracted
+   */
+  virtual Encoder::Status encode(CborEncoder* encoder, Message *msg) = 0;
+
+private:
+  const CBORTag tag;
+  const MessageId id;
+
+  friend CBORMessageEncoderSingleton;
+
+  /**
+   * Encode wrapper function that encodes the cbor tag and then calls the encode virtual function
+   *
+   * @param encoder tinycbor encoder struct
+   * @param msg     The message from which data must be extracted
+   */
+  Encoder::Status _encode(CborEncoder* encoder, Message *msg);
+};
+
+/**
+ * This class is a singleton. It collects CBORMessageEncoderInterfaces implementations to encode
+ * all possible CBOR encoded messages
+ */
+class CBORMessageEncoderSingleton: public Encoder {
+public:
+  /**
+   * Get the singleton instance
+   */
+  static CBORMessageEncoderSingleton& getInstance();
+
+  /**
+   * Add a new encoder to the singleton instance associating it to the provided cbor tag
+   *
+   * @param tag     the tag to which we associate the encoder
+   * @param encoder the instance of encoder to append
+   */
+  void append(MessageId id, CBORMessageEncoderInterface* encoder);
+
+  /**
+   * Encode a message and put the contents into a byte buffer. The message should be big enough
+   * to accommodate the content of the buffer.
+   *
+   * @param[in] msg     A struct that embeds struct Message
+   * @param[in out] buf The output buffer onto which the message will be encoded
+   * @param[in out] len The length of the buffer
+   */
+  Encoder::Status encode(Message* message, uint8_t * data, size_t& len);
+private:
+  CBORMessageEncoderSingleton() {}
+
+  std::vector<std::pair<MessageId, CBORMessageEncoderInterface*>> encoders;
+};
+
+/**
+ * In order to encode a message one can instantiate `CBORMessageEncoder` and
+ * call the encode function. In the future this class will contain encode session related
+ * information, in order to allow streaming decoding
+ */
+class CBORMessageEncoder: public Encoder {
+public:
+  /**
+   * Encode a message and put the contents into a byte buffer. The message should be big enough
+   * to accommodate the content of the buffer.
+   *
+   * @param[in] msg     A struct that embeds struct Message
+   * @param[in out] buf The output buffer onto which the message will be encoded
+   * @param[in out] len The length of the buffer
+   */
+  inline Encoder::Status encode(Message* msg, uint8_t* buf, size_t &len) {
+    return CBORMessageEncoderSingleton::getInstance().encode(msg, buf, len);
+  }
+};