How to read large responses in Boost::asio::read?

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I don't understand how to count a very large response with a GET request from boost::asio. I do char buffer[1024] the answer does not fit. as a result takes off exception. and if I make a buffer 4096, then the application freezes. in the while loop, the title is read first, I look for Content-Length and read the length. the response comes in the form of a header and then a Json body. how to make it read sooo big answer?