code: func (c *Client) sendPostRequest(httpReq *http.Request, jReq *jsonRequest) {
  	// Don't send the message if shutting down.
  	select {
  	case <-c.shutdown:
  		jReq.responseChan <- &response{result: nil, err: ErrClientShutdown}
  	default:
  	}
  
  	c.sendPostChan <- &sendPostDetails{
  		jsonRequest: jReq,
  		httpRequest: httpReq,
  	}
  }
docs: // sendPostRequest sends the passed HTTP request to the RPC server using the
  // HTTP client associated with the client.  It is backed by a buffered channel,
  // so it will not block until the send channel is full.