mpd-backend-dashboard/server.mjs

import fs from 'node:fs';
import https from 'node:https';
import net from 'node:net';

const MPD_HOST =
  process.env.MPD_HOST ?? '127.0.0.1';

const MPD_PORT =
  Number(process.env.MPD_PORT ?? '6600');

const MPD_TIMEOUT_MS =
  Number(process.env.MPD_TIMEOUT_MS ?? '700');

const POLL_INTERVAL_MS =
  Number(process.env.POLL_INTERVAL_MS ?? '1000');

const TLS_CERT_FILE =
  process.env.TLS_CERT_FILE ?? '/var/run/tls/tls.crt';

const TLS_KEY_FILE =
  process.env.TLS_KEY_FILE ?? '/var/run/tls/tls.key';

const state = {
  available: false,
  current: null,
  previous: [],
  error: 'Waiting for MPD',
  updatedAt: null,
};

let pollRunning = false;

const songDisplay = (fields) => {
  const artist =
    fields.Artist ??
    fields.AlbumArtist ??
    '';

  const title =
    fields.Title ??
    fields.Name ??
    fields.file ??
    'Unknown';

  return artist
    ? `${artist} - ${title}`
    : title;
};

const parseSong = (raw) => {
  const fields = {};

  for (const line of raw.split(/\r?\n/)) {
    if (
      !line ||
      line === 'OK' ||
      line.startsWith('OK MPD ')
    ) {
      continue;
    }

    if (line.startsWith('ACK ')) {
      throw new Error(line);
    }

    const separator = line.indexOf(': ');

    if (separator === -1) {
      continue;
    }

    const key = line.slice(0, separator);
    const value = line.slice(separator + 2);

    if (fields[key] === undefined) {
      fields[key] = value;
    }
  }

  if (
    !fields.file &&
    !fields.Title &&
    !fields.Name
  ) {
    return null;
  }

  const display = songDisplay(fields);

  return {
    id: [
      fields.file ?? '',
      fields.Artist ?? '',
      fields.Title ?? '',
      fields.Name ?? '',
    ].join('\u0000'),

    display,
    artist: fields.Artist ?? null,
    title: fields.Title ?? null,
    file: fields.file ?? null,
  };
};

const getCurrentSong = () =>
  new Promise((resolve, reject) => {
    const socket = net.createConnection({
      host: MPD_HOST,
      port: MPD_PORT,
    });

    socket.setEncoding('utf8');
    socket.setTimeout(MPD_TIMEOUT_MS);

    let buffer = '';
    let commandSent = false;
    let finished = false;

    const fail = (error) => {
      if (finished) {
        return;
      }

      finished = true;
      socket.destroy();
      reject(error);
    };

    const complete = (song) => {
      if (finished) {
        return;
      }

      finished = true;
      socket.end();
      resolve(song);
    };

    socket.on('timeout', () => {
      fail(
        new Error(
          `MPD did not respond within ${MPD_TIMEOUT_MS} ms`,
        ),
      );
    });

    socket.on('error', fail);

    socket.on('data', (chunk) => {
      buffer += chunk;

      if (!commandSent) {
        const newline = buffer.indexOf('\n');

        if (newline === -1) {
          return;
        }

        const greeting =
          buffer.slice(0, newline).trim();

        if (!greeting.startsWith('OK MPD ')) {
          fail(
            new Error(
              `Invalid MPD greeting: ${greeting}`,
            ),
          );
          return;
        }

        buffer = buffer.slice(newline + 1);

        commandSent = true;
        socket.write('currentsong\n');
      }

      if (
        buffer === 'OK\n' ||
        buffer.endsWith('\nOK\n')
      ) {
        try {
          complete(parseSong(buffer));
        } catch (error) {
          fail(error);
        }
      }

      if (buffer.includes('\nACK ')) {
        fail(new Error(buffer.trim()));
      }
    });

    socket.on('close', () => {
      if (!finished) {
        fail(
          new Error(
            'MPD connection closed unexpectedly',
          ),
        );
      }
    });
  });

const pollMPD = async () => {
  if (pollRunning) {
    return;
  }

  pollRunning = true;

  try {
    const nextSong = await getCurrentSong();

    const currentId =
      state.current?.id ?? null;

    const nextId =
      nextSong?.id ?? null;

    if (currentId !== nextId) {
      if (state.current) {
        state.previous = [
          {
            display: state.current.display,
            artist: state.current.artist,
            title: state.current.title,
            file: state.current.file,
          },
          ...state.previous,
        ].slice(0, 5);
      }

      state.current = nextSong;
    }

    state.available = true;
    state.error = null;
    state.updatedAt =
      new Date().toISOString();
  } catch (error) {
    state.available = false;
    state.error =
      error instanceof Error
        ? error.message
        : String(error);

    state.updatedAt =
      new Date().toISOString();
  } finally {
    pollRunning = false;
  }
};

await pollMPD();

setInterval(
  pollMPD,
  POLL_INTERVAL_MS,
);

const server = https.createServer(
  {
    cert: fs.readFileSync(TLS_CERT_FILE),
    key: fs.readFileSync(TLS_KEY_FILE),
  },
  (req, res) => {
    res.setHeader(
      'Content-Type',
      'application/json',
    );

    if (req.url === '/healthz') {
      res.writeHead(200);
      res.end(
        JSON.stringify({
          status: 'ok',
        }),
      );
      return;
    }

    if (req.url === '/api/status') {
      const current = state.current
        ? {
            display: state.current.display,
            artist: state.current.artist,
            title: state.current.title,
            file: state.current.file,
          }
        : null;

      res.writeHead(200);

      res.end(
        JSON.stringify({
          available: state.available,
          current,
          previous: state.previous,
          error: state.error,
          updatedAt: state.updatedAt,
        }),
      );

      return;
    }

    res.writeHead(404);
    res.end(
      JSON.stringify({
        error: 'Not found',
      }),
    );
  },
);

server.listen(9443, '0.0.0.0', () => {
  console.log(
    `MPD status server listening on :9443, MPD=${MPD_HOST}:${MPD_PORT}`,
  );
});