proxy-server.js

const express = require('express');
const bodyParser = require('body-parser');
const gremlin = require('gremlin');
const cors = require('cors');
const path = require('path');
const app = express();
const port = 3001;

app.use(cors({
  credentials: true,
}));

// parse application/json
app.use(bodyParser.json());

function mapToObj(inputMap) {
  let obj = {};

  inputMap.forEach((value, key) => {
    obj[key] = value
  });

  return obj;
}

function edgesToJson(edgeList) {
  return edgeList.map(
    edge => ({
      id: typeof edge.get('id') !== "string" ? JSON.stringify(edge.get('id')) : edge.get('id'),
      from: edge.get('from'),
      to: edge.get('to'),
      label: edge.get('label'),
      properties: mapToObj(edge.get('properties')),
    })
  );
}

function nodesToJson(nodeList) {
  return nodeList.map(
    node => ({
      id: node.get('id'),
      label: node.get('label'),
      properties: mapToObj(node.get('properties')),
      edges: edgesToJson(node.get('edges'))
    })
  );
}

function makeQuery(query, nodeLimit) {
  const nodeLimitQuery = !isNaN(nodeLimit) && Number(nodeLimit) > 0 ? `.limit(${nodeLimit})`: '';
  return `${query}${nodeLimitQuery}
  .dedup()
  .as('node')
  .project('id', 'label', 'properties', 'edges')
  .by(__.id())
  .by(__.label())
  .by(__.valueMap())
  .by(__.outE()
        .project('id', 'from', 'to', 'label', 'properties')
        .by(__.id())
        .by(__.select('node').id())
        .by(__.inV().id())
        .by(__.label())
        .by(__.valueMap())
        .fold()
  )`;
}

app.post('/query', (req, res, next) => {
  const gremlinHost = req.body.host;
  const gremlinPort = req.body.port;
  const nodeLimit = req.body.nodeLimit;
  const query = req.body.query;
  const traversalSource = req.body.traversalSource;

  const client = new gremlin.driver.Client(`ws://${gremlinHost}:${gremlinPort}/gremlin`, { traversalSource: traversalSource, mimeType: 'application/json' });

  client.submit(makeQuery(query, nodeLimit), {})
    .then((result) => res.send(nodesToJson(result._items)))
    .catch((err) => next(err));

});

app.get('/settings', (_, res) => {
  return res.json({
    GREMLIN_HOST: firstNotNull(process.env.GREMLIN_HOST, 'localhost'),
    GREMLIN_PORT: firstNotNull(process.env.GREMLIN_PORT, '8182'),
    GREMLIN_TRAVERSAL_SOURCE: firstNotNull(process.env.GREMLIN_TRAVERSAL_SOURCE, 'g'),
    GREMLIN_DEFAULT_QUERY: firstNotNull(process.env.GREMLIN_DEFAULT_QUERY, 'g.V()'),
  });
});

// Hosting react app in express 
// https://create-react-app.dev/docs/deployment#other-solutions
app.use(express.static(path.join(__dirname, 'frontend')));

app.get('/', function (_, res) {
  res.sendFile(path.join(__dirname, 'frontend', 'index.html'));
});

app.listen(port, () => console.log(`Simple gremlin-proxy server listening on port ${port}!`));

function firstNotNull() {
  for (let i = 0; i < arguments.length; i++) {
    const arg = arguments[i];
    if (arg) {
      return arg;
    }
  }
}