running_status.hpp

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#pragma once
 
// MIDI 1.0 running-status byte-stream parser.
//
// Platform MIDI backends (ALSA raw MIDI, Win32 mmeapi MIM_LONGDATA, BLE
// MIDI) deliver raw bytes — status bytes may be omitted when they would
// repeat the previous channel-voice status ("running status"). The prior
// ALSA MIDI parser had a simple state machine that didn't track running
// status, so a note-on sequence like `90 3C 7F 3D 7F 3E 7F` would emit
// only the first note. This parser handles running status, real-time
// interleave, and system-common/sysex boundaries correctly.
//
// Pure C++ — consumed by platform backends + unit-tested without any
// MIDI device attached.
//
// RT-safety contract:
//
//   - Install callbacks and call reserve_sysex(N) before entering the MIDI
//     callback, where N is the largest SysEx payload body the port accepts
//     after F0 and before F7.
//   - After that preparation, feed() and reset() do not allocate while SysEx
//     payloads stay within the reserved size.
//   - Callback objects and callback-owned destination storage are caller-owned.
//     Keep them preconstructed and allocation-free when using this parser from
//     realtime code.
 
#include <pulp/midi/message.hpp>
 
#include <cstddef>
#include <cstdint>
#include <functional>
#include <vector>
 
namespace pulp::midi {

using ShortMessageSink = std::function<void(const MidiEvent&)>;
using SysexSink        = std::function<void(const uint8_t* data, std::size_t size)>;
 
class RunningStatusParser {
public:
    RunningStatusParser() = default;
 
    void on_short_message(ShortMessageSink sink) { short_sink_ = std::move(sink); }
    void on_sysex(SysexSink sink) { sysex_sink_ = std::move(sink); }

    void reserve_sysex(std::size_t worst_case_body_bytes);

    void feed(const uint8_t* data, std::size_t size);

    void reset();
 
private:
    static int expected_data_bytes(uint8_t status);
    void emit_short(uint8_t status, uint8_t d1, uint8_t d2);
 
    uint8_t running_status_ = 0;        
    uint8_t current_system_common_ = 0; 
    uint8_t data_[2] = {0, 0};
    int data_count_ = 0;
    int data_expected_ = 0;             
    bool in_sysex_ = false;
    std::vector<uint8_t> sysex_buf_;
 
    ShortMessageSink short_sink_;
    SysexSink        sysex_sink_;
};
 
}  // namespace pulp::midi