Boost asio async_read_until stop reading on matched condition

Question

I have a general question about using boost asio's async_read_until. The documentation says there might be more data inside the buffer when the handler is called. Is there any way to work around this and stop the buffer from consuming bytes from the socket right after the sequence condition was matched?

Answer 1

Q. Is there any way to work around this

Not directly, because of the way network traffic works (it's packet oriented).

Of course, you might get things on the protocol boundary if the sending party actively ensures it, but that's unusual for stream protocols.

Q. and stop the buffer from consuming bytes from the socket right after the sequence condition was matched?

No, but you can stop consuming the buffer. So, e.g. this is a valid pattern:

boost::asio::streambuf sb;
auto bytes = boost::asio::read_until(socket, sb, "\r\n\r\n");

std::istream is(&sb);
std::string line;
while (getline(is, line) && !line.empty())    {
     std::cout << "Received: '" << line << "'\n";
}

// sb still contains un-consumed data, if any

Simply use the same streambuf for any subsequent reads and it will manage the "stream position" for you.