esp-protocols/components/esp_modem/include/cxx_include/esp_modem_cmux.hpp

// Copyright 2021 Espressif Systems (Shanghai) PTE LTD
//
// Licensed 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.

#pragma once

#include "esp_modem_terminal.hpp"

namespace esp_modem {

constexpr size_t MAX_TERMINALS_NUM = 2;
/**
 * @defgroup ESP_MODEM_CMUX ESP_MODEM CMUX class
 * @brief Definition of CMUX terminal
 */
/** @addtogroup ESP_MODEM_CMUX
* @{
*/

/**
 * @brief CMUX state machine
 */
enum class cmux_state {
    INIT,
    HEADER,
    PAYLOAD,
    FOOTER,
    RECOVER,
};

/**
 * @brief CMUX terminal abstraction
 *
 * This class inherits from Terminal class, as it is a Terminal, but is also composed of another Terminal,
 * which is used to communicate with the modem, i.e. the original Terminal which has been multiplexed.
 *
 * @note Implementation of CMUX protocol is experimental
 */
class CMuxInstance;

/**
 * @brief CMux class which consumes the original terminal and creates multiple virtual terminals from it.
 * This class itself is not usable as a DTE terminal, only via its instances defined in `CMuxInstance`
 */
class CMux {
public:
    explicit CMux(std::unique_ptr<Terminal> t, std::unique_ptr<uint8_t[]> b, size_t buff_size):
        term(std::move(t)), payload_start(nullptr), total_payload_size(0), buffer_size(buff_size), buffer(std::move(b))  {}
    ~CMux() = default;

    /**
     * @brief Initializes CMux protocol
     * @return true on success
     */
    [[nodiscard]] bool init();

    /**
     * @brief Sets read callback for the appropriate terminal
     * @param inst Index of the terminal
     * @param f function pointer
     */
    void set_read_cb(int inst, std::function<bool(uint8_t *data, size_t len)> f);

    /**
     * @brief Writes to the appropriate terminal
     * @param i Index of the terminal
     * @param data Data to write
     * @param len Data length to write
     * @return The actual written length
     */
    int write(int i, uint8_t *data, size_t len);

private:
    static uint8_t fcs_crc(const uint8_t frame[6]);     /*!< Utility to calculate FCS CRC */
    void data_available(uint8_t *data, size_t len);     /*!< Called when valid data available */
    void send_sabm(size_t i);                           /*!< Sending initial SABM */
    bool on_cmux(uint8_t *data, size_t len);            /*!< Called from terminal layer when raw CMUX protocol data available */

    struct CMuxFrame;                                   /*!< Forward declare the Frame struct, used in protocol decoders */
    /**
     * These methods serve different states of the CMUX protocols
     * @param frame Currently available cmux frame (basically data, size, methods)
     * @return - true if the state processed successfully
     *         - false if more data needed to process the current state
     */
    bool on_recovery(CMuxFrame &frame);
    bool on_init(CMuxFrame &frame);
    bool on_header(CMuxFrame &frame);
    bool on_payload(CMuxFrame &frame);
    bool on_footer(CMuxFrame &frame);

    std::function<bool(uint8_t *data, size_t len)> read_cb[MAX_TERMINALS_NUM];  /*!< Function pointers to read callbacks */
    std::unique_ptr<Terminal> term;                   /*!< The original terminal */
    cmux_state state;                                 /*!< CMux protocol state */

    /**
     * CMux control fields and offsets
     */
    uint8_t dlci;
    uint8_t type;
    size_t payload_len;
    uint8_t frame_header[6];
    size_t frame_header_offset;
    uint8_t *payload_start;
    size_t total_payload_size;
    int instance;
    int sabm_ack;

    /**
     * Processing buffer size and pointer
     */
    size_t buffer_size;
    std::unique_ptr<uint8_t[]> buffer;

    Lock lock;
};

/**
 * @brief This represents a specific instance of a CMUX virtual terminal. This class also implements Terminal interface
 * and as such could be used as a DTE's terminal.
 */
class CMuxInstance: public Terminal {
public:
    explicit CMuxInstance(std::shared_ptr<CMux> parent, int i): cmux(std::move(parent)), instance(i) {}

    int write(uint8_t *data, size_t len) override
    {
        return cmux->write(instance, data, len);
    }
    void set_read_cb(std::function<bool(uint8_t *data, size_t len)> f) override
    {
        return cmux->set_read_cb(instance, std::move(f));
    }
    int read(uint8_t *data, size_t len) override
    {
        return  0;
    }
    void start() override { }
    void stop() override { }
private:
    std::shared_ptr<CMux> cmux;
    size_t instance;
};

/**
 * @}
 */

} // namespace esp_modem