JsonPostPromise.js

const uWS = require('uWebSockets.js');
const port = 9001;

const app = uWS./*SSL*/App({
}).post('/*', async (res, req) => {

  /* Note that you cannot read from req after returning from here */
  let url = req.getUrl();

  res.onAborted(() => {
    res.aborted = true;
  });

  let jsonData;

  try {
    jsonData = await readJson(res);
  } catch (e) {
    console.log('Invalid JSON or no data at all!');
    res.close();
    return;
  }

  console.log('Posted to ' + url + ': ');
  console.log(jsonData);
  
  try {
    console.log(req.getHeader('accept'));
  } catch (e) {
    // error will be caught
    // error reading header Using uWS.HttpRequest past its request handler return is forbidden (it is stack allocated).
    console.log(`error reading header ${e}`);
    return;
  }

  if (res.aborted) {
    return;
  }

  res.end('Thanks for this json!');
}).listen(port, (token) => {
  if (token) {
    console.log('Listening to port ' + port);
  } else {
    console.log('Failed to listen to port ' + port);
  }
});

/* Helper function for reading a posted JSON body */
function readJson(res) {
  let buffer;

  return new Promise((resolve, reject) => {
    res.onData((ab, isLast) => {
      let chunk = Buffer.from(ab);
      if (isLast) {
        let json;
        if (buffer) {
          try {
            json = JSON.parse(Buffer.concat([buffer, chunk]));
          } catch (e) {
            reject(e);
          }
          resolve(json);
        } else {
          try {
            json = JSON.parse(chunk);
          } catch (e) {
            reject(e);
          }
          resolve(json);
        }
      } else {
        if (buffer) {
          buffer = Buffer.concat([buffer, chunk]);
        } else {
          buffer = Buffer.concat([chunk]);
        }
      }
    });
  });
}