Easiest way to implement a true boost::asio::async_read_until

Question

What's the easiest way to implement a version of boost::asio::async_read_until that only reads until the delimiter is found? Can I implement a special match condition that knows how to consume the proper amount of bytes? If not, then how to I write an async reader that checks each byte?

I need to stop the provided streambuf from consuming bytes beyond the delimiter.

Adriano Repetti Adriano Repetti · Accepted Answer · 2012-03-27T15:01:51

In the documentation you can find a simple match function:

std::pair<iterator, bool>
match_whitespace(iterator begin, iterator end)
{
  iterator i = begin;
  while (i != end)
    if (std::isspace(*i++))
      return std::make_pair(i, true);
  return std::make_pair(i, false);
}

In this case it matches any whitespace (change std::isspace according to what you want). Again in that documentation you can see a more complex event, it consumes the stream until it finds a specific character:

class match_char
{
public:
  explicit match_char(char c) : c_(c) {}

  template <typename Iterator>
  std::pair<Iterator, bool> operator()(
      Iterator begin, Iterator end) const
  {
    Iterator i = begin;
    while (i != end)
      if (c_ == *i++)
        return std::make_pair(i, true);
    return std::make_pair(i, false);
  }

private:
  char c_;
};

And the code to use that class:

// Function used for error handling
void handler(const boost::system::error_code& e, std::size_t size)
{
 // Do something
}

// Example of call, it reads from inputStream to outputStreamBuff
// until the specified delimiter (";") is found
boost::asio::async_read_until(inputStream, outputStreamBuff,
   match_char(';'), handler);

Easiest way to implement a true boost::asio::async_read_until

3 Answers