MeshBot/src/mesh/codec.ts

import { create, fromBinary, toBinary } from '@bufbuild/protobuf';

let proto: typeof import('@meshtastic/protobufs') | null = null;

async function loadProto(): Promise<typeof import('@meshtastic/protobufs')> {
  if (!proto) proto = await import('@meshtastic/protobufs');
  return proto!;
}

export const BROADCAST_ADDR = 0xffffffff;
// official portnums.proto: TEXT_MESSAGE_APP=1 (task spec draft said 3 — the enum value wins)
export const PORT_TEXT_MESSAGE_APP = 1;
// verified against installed @meshtastic/protobufs Portnums.PortNum.POSITION_APP
export const PORT_POSITION_APP = 3;
// verified against installed @meshtastic/protobufs Portnums.PortNum.ROUTING_APP
export const PORT_ROUTING_APP = 5;

const START1 = 0x94;
const START2 = 0xc3;
const MAX_LEN = 1024;

export function extractFrames(buf: Uint8Array): {
  packets: Uint8Array[];
  rest: Uint8Array;
} {
  const packets: Uint8Array[] = [];
  let i = 0;
  for (;;) {
    if (i >= buf.length) return { packets, rest: new Uint8Array(0) };
    const isHeaderStart =
      buf[i] === START1 && i + 1 < buf.length && buf[i + 1] === START2;
    if (!isHeaderStart) {
      // keep a trailing lone 0x94 — it may be the first byte of a split header
      if (buf[i] === START1 && i + 1 >= buf.length)
        return { packets, rest: buf.subarray(i) };
      i++;
      continue;
    }
    if (i + 4 > buf.length) return { packets, rest: buf.subarray(i) }; // partial header
    const len = (buf[i + 2] << 8) | buf[i + 3];
    if (len > MAX_LEN) {
      i++; // bogus header — rescan from next byte
      continue;
    }
    if (i + 4 + len > buf.length) return { packets, rest: buf.subarray(i) }; // partial payload
    packets.push(buf.subarray(i + 4, i + 4 + len));
    i += 4 + len;
  }
}

export function frame(payload: Uint8Array): Uint8Array {
  const out = new Uint8Array(4 + payload.length);
  out[0] = START1;
  out[1] = START2;
  out[2] = (payload.length >> 8) & 0xff;
  out[3] = payload.length & 0xff;
  out.set(payload, 4);
  return out;
}

export async function decodeFromRadio(
  bytes: Uint8Array,
): Promise<import('@meshtastic/protobufs').Mesh.FromRadio> {
  const P = await loadProto();
  return fromBinary(P.Mesh.FromRadioSchema, bytes);
}

/** POSITION_APP packets carry a serialized meshtastic.Position in Data.payload. */
export async function decodePosition(
  bytes: Uint8Array,
): Promise<import('@meshtastic/protobufs').Mesh.Position> {
  const P = await loadProto();
  return fromBinary(P.Mesh.PositionSchema, bytes);
}

/** ROUTING_APP packets carry a serialized meshtastic.Routing in Data.payload (ACK/NACK for want_ack sends). */
export async function decodeRouting(
  bytes: Uint8Array,
): Promise<import('@meshtastic/protobufs').Mesh.Routing> {
  const P = await loadProto();
  return fromBinary(P.Mesh.RoutingSchema, bytes);
}

/** Human-readable name for a Routing.Error code (from the installed @meshtastic/protobufs enum), `reason <n>` fallback. */
export async function describeRoutingError(code: number): Promise<string> {
  const P = await loadProto();
  const hit = Object.entries(P.Mesh.Routing_Error).find(
    ([, v]) => typeof v === 'number' && v === code,
  );
  return hit ? String(hit[0]) : `reason ${code}`;
}

let hwModelNames: Map<number, string> | null = null;
/** Reverse lookup of meshtastic.HardwareModel (enum value -> name), loaded once. */
export async function loadHwModelNames(): Promise<Map<number, string>> {
  if (!hwModelNames) {
    const P = await loadProto();
    hwModelNames = new Map(
      Object.entries(P.Mesh.HardwareModel).map(([k, v]) => [
        Number(k),
        String(v),
      ]),
    );
  }
  return hwModelNames;
}

export async function buildTextToRadio(
  to: number,
  text: string,
  channelIndex: number,
): Promise<{ bytes: Uint8Array; id: number }> {
  const P = await loadProto();
  let id = Math.floor(Math.random() * 0x100000000) >>> 0;
  if (id === 0) id = 1; // non-zero uint32
  const meshPacket = create(P.Mesh.MeshPacketSchema, {
    to,
    id,
    wantAck: true,
    channel: channelIndex,
    payloadVariant: {
      case: 'decoded',
      value: {
        portnum: P.Portnums.PortNum.TEXT_MESSAGE_APP,
        payload: new TextEncoder().encode(text),
        wantResponse: true,
      },
    },
  });
  const toRadio = create(P.Mesh.ToRadioSchema, {
    payloadVariant: { case: 'packet', value: meshPacket },
  });
  return { bytes: frame(toBinary(P.Mesh.ToRadioSchema, toRadio)), id };
}

export async function buildWantConfigToRadio(
  wantConfigId: number,
): Promise<Uint8Array> {
  const P = await loadProto();
  const toRadio = create(P.Mesh.ToRadioSchema, {
    payloadVariant: { case: 'wantConfigId', value: wantConfigId },
  });
  return toBinary(P.Mesh.ToRadioSchema, toRadio);
}