`midi-contract/midi-message`

Purpose

Defines the local mirror of the @suaveplan/midi MidiMessage discriminated union plus its peer types (Channel, MidiPortLike, NRPNChange, RPNChange, CC14Change, Unsubscribe). This file exists so @suaveplan/react-midi can be developed and tested on its own branch while @suaveplan/midi is being authored in parallel on feat/midi. Once both branches land, the type aliases here SHALL be replaced by a re-export from @suaveplan/midi; no shape change is intended at swap time.

Features

Channel-voice variants: noteOn, noteOff, polyAftertouch, controlChange, programChange, channelPressure, pitchBend.
System variants: sysEx, clock, start, continue, stop, activeSensing, systemReset.
High-resolution reducer events: NRPNChange, RPNChange, CC14Change.
Structural MidiPortLike interface compatible with any transport.

Usage: Basic

import type { MidiMessage } from "@suaveplan/react-midi/midi-contract";

function isNote(msg: MidiMessage): boolean {
    return msg.type === "noteOn" || msg.type === "noteOff";
}

Usage: Advanced

import type { MidiPortLike } from "@suaveplan/react-midi/midi-contract";

class FakePort implements MidiPortLike {
    readonly id = "fake-1";
    readonly name = "Fake In";
    readonly state = "connected" as const;
    private subs = new Set<(m: MidiMessage) => void>();
    send(_: Uint8Array): void {}
    onMessage(handler: (m: MidiMessage) => void) {
        this.subs.add(handler);
        return () => this.subs.delete(handler);
    }
}

API Reference

Channel = 0..15 literal union.
MidiMessage discriminated union — see Features.
MidiMessageType = MidiMessage["type"].
MidiPortLike { id, name, manufacturer?, state, send, onMessage }.
NRPNChange, RPNChange, CC14Change — reducer outputs.
Unsubscribe = () => void.

Implementation Notes

The file deliberately uses interface declarations (not type aliases) for variant shapes so each one can be discriminated in user code by hovering over the inferred type. The structural MidiPortLike mirrors the Web MIDI shape but adds a manufacturer field and a typed onMessage that yields parsed MidiMessage rather than raw bytes — that lift is performed inside port/web-midi-port.ts.

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midi-contract/midi-message