docs: function buildUpyunReceiverStream(opts) {
    var options = opts || {};
  
    _.defaults(options, {
  
      endpoing: 'v0',
      apiVersion: 'legacy',
  
      // Upload limit (in bytes)
      // defaults to ~15MB
      maxBytes: 15000000,
  
      // Upload limit for per coming file (in bytes)
      // falsy means no limit
      perMaxBytes: 15000000,
  
      // Upload limit for per file (in content-type)
      // falsy means accept all the type
      acceptTypes: null,
  
    });
  
    var receiver__ = WritableStream({ objectMode: true });
  
    // if onProgress handler was provided, bind an event automatically:
    if (_.isFunction(options.onProgress)) {
      receiver__.on('progress', options.onProgress);
    }
  
    // Track the progress of all file uploads that pass through this receiver
    // through one or more attached Upstream(s).
    receiver__._files = [];
  
    // This `_write` method is invoked each time a new file is received
    // from the Readable stream (Upstream) which is pumping filestreams
    // into this receiver.  (filename === `__newFile.filename`).
    receiver__._write = onFile.bind({ options });
  
    return receiver__;
  }