codec_hdlc.h

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// Copyright 2024-2025 The Aerospace Corporation.
// This file is a part of SatCat5, licensed under CERN-OHL-W v2 or later.
 
#pragma once
 
#include <satcat5/crc16_checksum.h>
#include <satcat5/eth_checksum.h>
#include <satcat5/io_checksum.h>
 
namespace satcat5 {
    namespace io {
        class HdlcEncoder : public satcat5::io::WriteableRedirect {
        public:
            explicit HdlcEncoder(satcat5::io::Writeable* dst);
 
            inline void set_mode_actrl(bool actrl)
                { m_bstuff.m_actrl = actrl; }
 
            void set_mode_crc32(bool mode32);
 
        private:
            // Helper class for byte-stuffing.
            class ByteStuff : public satcat5::io::Writeable {
            public:
                explicit ByteStuff(satcat5::io::Writeable* dst);
                unsigned get_write_space() const override;
                void write_abort() override;
                bool write_finalize() override;
                void write_next(u8 data) override;
                satcat5::io::Writeable* const m_dst;    // Output object
                bool m_actrl;                           // Escape < 0x20?
            } m_bstuff;
 
            // Append checksum using the selected algorithm.
            satcat5::eth::ChecksumTx m_crc32;
            satcat5::crc16::KermitTx m_crc16;
        };
 
        class HdlcDecoder : public satcat5::io::Writeable {
        public:
            explicit HdlcDecoder(satcat5::io::Writeable* dst);
 
            // Implement required API from Writeable:
            unsigned get_write_space() const override;
 
            inline void set_mode_actrl(bool actrl)
                { m_actrl = actrl; }
 
            void set_mode_crc32(bool mode32);
 
        private:
            // Implement required API from Writeable:
            void write_next(u8 data) override;
            void write_overflow() override;
 
            // Verify checksum using the selected algorithm.
            satcat5::eth::ChecksumRx m_crc32;
            satcat5::crc16::KermitRx m_crc16;
 
            // Internal state:
            enum class State {HDLC_RDY, HDLC_ESC, HDLC_EOF, HDLC_ERR};
            satcat5::io::HdlcDecoder::State m_state;    // Decoder state
            bool m_actrl;                               // Escape < 0x20?
            satcat5::io::Writeable* m_crc;              // CRC16 or CRC32?
        };
    }
}