intercepting body stream makes request.js not setting header of response

[TooBug]

in koa-logger, it replaces ctx.body with a Counter:

    if (length == null && body && body.readable) {
      ctx.body = body
        .pipe(counter = Counter())
        .on('error', ctx.onerror)
    }

in request.js, it will add headers to dest stream if it supports setHeader() method:

  // here, if koa-logger is used, dest.setHeader is undefined.

  if (dest.setHeader && !dest.headersSent) {
    for (var i in response.headers) {
      // If the response content is being decoded, the Content-Encoding header
      // of the response doesn't represent the piped content, so don't pass it.
      if (!self.gzip || i !== 'content-encoding') {
        dest.setHeader(i, response.headers[i])
      }
    }
    dest.statusCode = response.statusCode
  }

so, if we use ctx.body = request() and request() returns a stream, the headers from request() stream are lost.