run-node-python-server.ts

import path from 'path';
import express from 'express';
import fileUpload from 'express-fileupload';

import { pythonRunningProcess, spawnPythonProcess } from './spawn-python-process';
import { useRunningPythonServer } from './use-running-python-server';

const downloadsFolder = path.resolve(__dirname, './downloads');

let isProcessing = false;
const requestQueue: Array<{
  filePath: string;
  res: any; // Express response
}> = [];

async function processQueue() {
  if (requestQueue.length === 0) {
    isProcessing = false;
    return;
  }

  isProcessing = true;
  const firstEntry = requestQueue.shift();
  if (!firstEntry) {
    return;
  }

  const { filePath, res } = firstEntry;

  try {
    const solution = await useRunningPythonServer(filePath);
    console.log('solution: ', solution);
    res.status(200).send(solution);
    processQueue();
  } catch (error) {
    res.status(500).send(error);
    console.error(error);
    processQueue();
  }
}

async function handleFileUpload(req, res) {
  try {
    if (!pythonRunningProcess) {
      return res.status(500).send('python process is not running');
    }
    if (!req.files || Object.keys(req.files).length === 0) {
      return res.status(400).send('No files were uploaded');
    }
    if (Object.keys(req.files).length > 1) {
      return res.status(400).send('Provide a single file');
    }

    const imageFile = req.files.imageFile;
    const fileName = `image-${Date.now()}.png`;
    const filePath = path.join(downloadsFolder, fileName);
    console.log('filePath: ', filePath);

    // Use the mv() method to place the file somewhere on your server
    imageFile.mv(filePath, async function (err) {
      if (err) {
        return res.status(500).send(err);
      }

      requestQueue.push({ filePath, res });

      if (isProcessing) {
        return;
      }

      processQueue();
    });
  } catch (err) {
    console.error(err);
    return res.status(500).send(err);
  }
}

export function runNodeListenerServer() {
  const app = express();
  app.use(
    fileUpload({
      limits: { fileSize: 20 * 1024 }, // 20 kb
    })
  );

  console.log('>>> runNodeListenerServer');
  const PORT = 3456;
  app.listen(PORT, () => {
    console.log(`Server listening on port ${PORT}`);
  });

  // spawn python process  only once simultaneously with the server;
  // reuse it multiple times later
  spawnPythonProcess();

  app.get('/recognise-image', (req, res) => res.status(200).send('python process is running'));
  app.post('/recognise-image', handleFileUpload);
}

runNodeListenerServer();