Boost C++ Libraries

Many commonly-used internet protocols are line-based, which means that they have protocol elements that are delimited by the character sequence "\r\n". Examples include HTTP, SMTP and FTP.

To more easily permit the implementation of line-based protocols, as well as other protocols that use delimiters, Boost.Asio includes the functions read_until() and async_read_until().

The following example illustrates the use of async_read_until() in an HTTP server, to receive the first line of an HTTP request from a client:

class http_connection
{
  ...

  void start()
  {
    asio::async_read_until(socket_, data_, "\r\n",
        boost::bind(&http_connection::handle_request_line, this, _1));
  }

  void handle_request_line(boost::system::error_code ec)
  {
    if (!ec)
    {
      std::string method, uri, version;
      char sp1, sp2, cr, lf;
      std::istream is(&data_);
      is.unsetf(std::ios_base::skipws);
      is >> method >> sp1 >> uri >> sp2 >> version >> cr >> lf;
      ...
    }
  }

  ...

  asio::ip::tcp::socket socket_;
  asio::streambuf data_;
};