How to manually place data in a boost::asio::streambuf to later read it with a std::istream?

I am trying to use a std::istream as data source. I want to place custom binary data in the istream's stream buffer so it can later be retrieved from the istream.

I have read about boost::asio::streambuf and how it is used to do exactly what I want but using a socket as data source instead of an in-memory buffer, which is what I would like to use.

From what I understand from the documentation, the steps should be:

1. Create a boost::asio::streambuf
2. Create a std::istream passing the streambuf
3. Invoke boost::asio::streambuf::prepare to get the list of buffers representing the output sequence.
4. Somehow write in the output 开发者_StackOverflow中文版sequence.
5. Invoke boost::asio::streambuf::commit to move what I wrote in the output sequence to the input sequence.
6. Read from the std::istream from step 2 normally with std::stream::read.

I don't know how to address step 4, so I don't know even if I'm going in the right direction.

Are the depicted steps correct? If so, how to address step 4?

You can easily send any std stream, so you can also you a stringstream. You can write binary data to your stringstream (it is just a byte array, effectively).

A few samples:

boost::asio::streambuf request;
std::ostream request_stream(&request);
request_stream.write(&binarydata_buf, sizeof(binarydata_buf));
// or use stream operators: request_stream << "xxx" << yyy;

// Send the request.
boost::asio::write(socket, request);

If you already have a fully populated istream (using std::cin as dummy in this example):

boost::asio::streambuf request;
std::ostream request_stream(&request);
request_stream << std::cin.rdbuf() << std::flush;

// Send the request.
boost::asio::write(socket, request);

Ways to populate an istream are e.g. ostream::write or Boost Serialization binary_archive

There are many ways to skin a cat of course, so be sure to think over the other options before blindly copying this.

See How to send ostream via boost sockets in C++?

Why not just transmit the data across a socket into your streambuf? If you can link the std::istream to the asio::streambuf which is listening on a particular socket, just use the same socket with boost::asio::write to send it data.

There isn't much penalty to using actual sockets intra-process, rather than trying to simulated it by accessing underlying data structures.