jsonImageUploadStream.js

const express = require('express');
const app = express();

app.post('/image-upload', (req, res) => {
  let body = '';
  let len = parseInt(req.get('content-length'), 10);
  req.on('data', chunk => {
    body += chunk;
  });
  req.on('end', () => {
    const chunkLen = parseInt(body.length, 10);
    const json = JSON.parse(body);
    var base64Data = json.url.replace(/^data:image\/png;base64,/, '');
    if (chunkLen === len) {
      require('fs').writeFile('out.png', base64Data, 'base64', function(err) {
        console.log(err);
      });
      return res.status(200).send('Upload file success.');
    }
    return res.status(200).send('Upload file failed.');
  });
});

app.listen(3001, () => {
  console.log('Server listen on port 3001');
});