codec_cobs.h

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// Copyright 2025 The Aerospace Corporation.
// This file is a part of SatCat5, licensed under CERN-OHL-W v2 or later.
 
#pragma once
 
#include <satcat5/io_buffer.h>
#include <satcat5/pkt_buffer.h>
 
// Default size parameters
// (Must be large enough for one full-size Ethernet frame + metadata,
//  larger sizes are fine if you have the memory for it.)
#ifndef SATCAT5_COBS_BUFFSIZE
#define SATCAT5_COBS_BUFFSIZE   1600    // One full-size Ethernet frame
#endif
 
#ifndef SATCAT5_COBS_PACKETS
#define SATCAT5_COBS_PACKETS    32      // ...or many smaller frames
#endif
 
namespace satcat5 {
    namespace io {
        class CobsEncoder : public satcat5::io::Writeable {
        public:
            explicit CobsEncoder(satcat5::io::Writeable* dst);
 
            // Implement required API from Writeable:
            unsigned get_write_space() const override;
            bool write_finalize() override;
            void write_overflow() override;
 
        private:
            // Implement required API from Writeable:
            void write_next(u8 data) override;
 
            // Flush the lookahead buffer.
            void flush_segment();
 
            // Internal state:
            satcat5::io::Writeable* const m_dst;    // Output object
            u8 m_ctr;                               // Run-length counter
            u8 m_ovr;                               // Overflow flag
            u8 m_buf[254];                          // Lookahead buffer
        };
 
        class CobsDecoder : public satcat5::io::Writeable {
        public:
            explicit CobsDecoder(satcat5::io::Writeable* dst);
 
            // Implement required API from Writeable:
            unsigned get_write_space() const override;
 
        private:
            // Implement required API from Writeable:
            void write_next(u8 data) override;
            void write_overflow() override;
 
            // Internal state:
            satcat5::io::Writeable* const m_dst;        // Output object
            u8 m_blk;                                   // Block type
            u8 m_ctr;                                   // Bytes remaining
            u8 m_ovr;                                   // Overflow flag
        };
 
        class CobsCodec
            : public satcat5::io::CobsEncoder
            , public satcat5::io::ReadableRedirect
        {
        public:
            CobsCodec(
                satcat5::io::Writeable* dst,
                satcat5::io::Readable* src);
 
        protected:
            satcat5::io::PacketBuffer m_buff;       
            satcat5::io::CobsDecoder m_decode;      
            satcat5::io::BufferedCopy m_copy;       
            u8 m_rawbuff[SATCAT5_COBS_BUFFSIZE];    
        };
 
        class CobsCodecInverse
            : public satcat5::io::CobsDecoder
            , public satcat5::io::ReadableRedirect
        {
        public:
            CobsCodecInverse(
                satcat5::io::Writeable* dst,
                satcat5::io::Readable* src);
 
        protected:
            satcat5::io::PacketBuffer m_buff;       
            satcat5::io::CobsEncoder m_encode;      
            satcat5::io::BufferedCopy m_copy;       
            u8 m_rawbuff[SATCAT5_COBS_BUFFSIZE];    
        };
    }
}