const { StringDecoder } = require('string_decoder');
const fs = require('fs');
const path = require('path');
function parseHeader(stream, callback) {
  stream.on('error', callback);
  stream.on('readable', onReadable);
  const decoder = new StringDecoder('utf8');
  let header = '';
  function onReadable() {
    let chunk;
    while (null !== (chunk = stream.read())) {
      const str = decoder.write(chunk);
      if (str.match(/\n\n/)) {
        // Found the header boundary.
        const split = str.split(/\n\n/);
        header += split.shift();
        const remaining = split.join('\n\n');
        const buf = Buffer.from(remaining, 'utf8');
        stream.removeListener('error', callback);
        // Remove the 'readable' listener before unshifting.
        stream.removeListener('readable', onReadable);
        if (buf.length)
          stream.unshift(buf);
        // Now the body of the message can be read from the stream.
        callback(null, header, stream);
        // return;
      } else {
        // Still reading the header.
        header += str;
      }
    }
  }
}

const fsStream = fs.createReadStream(path.resolve(__dirname, './sample'));
parseHeader(fsStream, (error, header, stream) => {
    console.log(error, header);
});