boost::asio async_read guarantee all bytes are read

Question

I have a server that receives a compressed string (compressed with zlib) from a client, and I was using async_receive from the boost::asio library to receive this string, it turns out however that there is no guarantee that all bytes will be received, so I now have to change it to async_read. The problem I face is that the size of the bytes received is variable, so I am not sure how to use async_read without knowing the number of bytes to be received. With the async_receive I just have a boost::array<char, 1024>, however this is a buffer that is not necessarily filled completely.

I wondered if anyone can suggest a solution where I can use async_read even though I do not know the number of bytes to be received in advance?

void tcp_connection::start(boost::shared_ptr<ResolverQueueHandler> queue_handler)
{
    if (!_queue_handler.get())
        _queue_handler = queue_handler;

    std::fill(buff.begin(), buff.end(), 0);

    //socket_.async_receive(boost::asio::buffer(buff), boost::bind(&tcp_connection::handle_read, shared_from_this(), boost::asio::placeholders::error));
    boost::asio::async_read(socket_, boost::asio::buffer(buff), boost::bind(&tcp_connection::handle_read, shared_from_this(), boost::asio::placeholders::error));
}

buff is a boost::array<char, 1024>

Answer 1

How were you expecting to do this using any other method?

There are a few general methods to sending data of variable sizes in an async manor:

1. By message - meaning that you have a header that defines the length of the expected message followed by a body which contains data of the specified length.
2. By stream - meaning that you have some marker (and this is very broad) method of knowing when you've gotten a complete packet.
3. By connection - each complete packet of data is sent in a single connection which is closed once the data is complete.

So can your data be parsed, or a length sent etc...

Answer 2

Use async_read_until and create your own match condition, or change your protocol to send a header including the number of bytes to expect in the compressed string.