drawio/lib/versioning/run_server.js

// NodeJS script

const fs = require('fs/promises');
const fsConstants = require('fs').constants;
const path = require('path');
const {EOL} = require('os');

const http = require('http');
const handler = require('serve-handler');

const IDLENGTH = 36; // UUID v4

const port = process.env.DRAWIOPORT || 8700;
const stateDir = process.env.DRAWIOSTATEDIR || ".";

async function startServer() {
  const opsDir = path.join(stateDir, 'ops');
  const sessionDir = path.join(stateDir, 'sessions');
  try {
    process.stdout.write("Can read/write in directory '" + opsDir + "' ? ...");
    await fs.access(opsDir, fsConstants.R_OK | fsConstants.W_OK);
    process.stdout.write("OK" + EOL);
    process.stdout.write("Can read/write in directory '" + sessionDir + "' ? ...");
    await fs.access(sessionDir, fsConstants.R_OK | fsConstants.W_OK);
    process.stdout.write("OK" + EOL);
  } catch (e) {
    process.stdout.write(EOL + "Please make sure the following directories exist and are writable:" + EOL);
    process.stdout.write("  " + opsDir + EOL);
    process.stdout.write("  " + sessionDir + EOL);
    process.exit(1);
  }

  const { WebSocketServer } = require('ws');
  const { v4: uuidv4 } = require("uuid");

  function asyncSleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
  }

  const httpServer = http.createServer((request, response) => {
    // You pass two more arguments for config and middleware
    // More details here: https://github.com/vercel/serve-handler#options
    console.log(request.method, request.url)
    return handler(request, response);
  });

  const wsServer = new WebSocketServer({
    server: httpServer,
    path: "/websocket",
  });

  // Provides async reads and writes to files, while guaranteeing that for every file, a read always reads the latest write.
  class QueuedIO {
    constructor(path) {
      this.path = path;
      this.queues = new Map();
    }
    _queuedIO(f, filename, ...args) {
      const lastIO = this.queues.get(filename) || Promise.resolve();
      const nextIO = lastIO.then(() => f(path.join(this.path, filename), ...args));
      this.queues.set(filename, nextIO.catch(e => {/*console.log("silently caught", e)*/}));
      return nextIO;
    }
    write(filename, data) {
      // console.log("writing file", filename);
      return this._queuedIO((path, data) => fs.writeFile(path, data, {encoding: 'utf8'}), filename, data);
    }
    append(filename, data) {
      // console.log("appending to file", filename);
      const result = this._queuedIO(fs.appendFile, filename, data);
      // result.then(() => console.log("success")).catch(e => console.log("COULD NOT APPEND", e));
      return result;
    }
    stat(filename) {
      // console.log("statting file", filename);
      return this._queuedIO(fs.stat, filename);
    }
    read(filename) {
      // console.log("reading file", filename);
      return this._queuedIO(path => fs.readFile(path, {encoding:'utf8'}), filename);
    }
    writeJSON(filename, json) {
      // console.log("writeJSONing file", filename);
      return this.write(filename, JSON.stringify(json));
    }
    readJSON(filename) {
      // console.log("readJSONing file", filename);
      return this.read(filename).then(JSON.parse);
    }
  }

  const opsDB = new QueuedIO(opsDir);
  const sessionDB = new QueuedIO(sessionDir);

  // mapping of modelId to set of sockets
  const subscriptions = new Map();

  wsServer.on('connection', function(socket) {
    console.log("Client connected.")
    const mySubscriptions = new Set();

    function join(sessionId) {
      const subbedSockets = subscriptions.get(sessionId);
      if (subbedSockets) {
        subbedSockets.add(socket);
      } else {
        subscriptions.set(sessionId, new Set([socket]));
      }
      mySubscriptions.add(sessionId);
    }
    function leave(sessionId) {
      const subbedSockets = subscriptions.get(sessionId);
      if (subbedSockets) {
        subbedSockets.delete(socket);
      }
      mySubscriptions.delete(sessionId);      
    }
    function leaveAll() {
      mySubscriptions.forEach(leave);
    }

    async function handle(req) {
      if (req.type === "ping") {
        return {type: "pong"};
      }
      else {
        console.log("-> ", req);

        if (req.type === "join") {
          const { reqId, sessionId } = req;
          leaveAll(); // a client can only join 1 session at a time
          join(sessionId);
          // Reply with all operations in session
          const session = await sessionDB.read(sessionId).catch(e => {
            if (e.code === 'ENOENT') {
              return ""; // Act as if session exists and is empty
            } else {
              throw e;
            }
          });
          const opIds = new Array(session.length / IDLENGTH);
          for (let i=0; i<opIds.length; i+=1) {
            const offset = i * IDLENGTH;
            opIds[i] = session.slice(offset, offset + IDLENGTH);
          }
          const ops = await Promise.all(opIds.map(async id => ({id, detail: await opsDB.readJSON(id)})));
          return {type: "ack", reqId, ops};
        }

        else if (req.type === "leave") {
          const { reqId } = req;
          leaveAll();
          return {type: "ack", reqId};
        }

        else if (req.type === "new_share") {
          const { reqId, ops } = req;
          const sessionId = uuidv4();
          leaveAll();
          join(sessionId);
          await Promise.all(ops.map(({id, detail}) => opsDB.writeJSON(id, detail)));
          await sessionDB.write(sessionId, ops.map(op=>op.id).join(''));
          return {type: "ack", reqId, sessionId};
        }

        else if (req.type === "new_edit") {
          const { reqId, sessionId, op: {id, detail} } = req;
          await opsDB.writeJSON(id, detail);
          await sessionDB.append(sessionId, id); // Creates file if it doesn't exist yet
          // Best effort broadcast to all subscribers
          (async () => {
            const subbedSockets = subscriptions.get(sessionId) || new Set();
            const broadcastMsg = {type:"pub_edit", sessionId, op: {id, detail}};
            console.log("BROADCAST to", subbedSockets.size-1,"subscribers...", broadcastMsg);
            const stringified = JSON.stringify(broadcastMsg);
            // await asyncSleep(3000);
            subbedSockets.forEach(subbed => {
              if (subbed !== socket) { // don't echo
                try {
                  subbed.send(stringified); // forward incoming request to all
                } catch (e) {
                  console.log("Error:", e, "Closing socket...")
                  subbed.close(); // in case of an error, it is the client's responsibility to re-subscribe and 'catch up'.
                }
              }
            });
          })();
          return {type: "ack", reqId};
        }
      }
    }

    socket.on('message', function(data) {
      const req = JSON.parse(data);
      handle(req).then(json => {
        if (json.type !== 'pong')
          console.log("<- ", json);
        socket.send(JSON.stringify(json));
      }).catch(e => {
        console.log("Error handling", req, e);
      })
    });

    socket.on('close', function() {
      leaveAll();
      console.log("Client disconnected.");
    })
  });

  httpServer.listen(port);
  console.log("Listening on", port);
}


startServer().catch(e => {
  console.log("Error in startServer:", e);
  process.exit(1);
});