flat_buffer copy constructor error after a call to flat_buffer::consume

[grenadium]

When compiling with beast from the boost 1.70 distribution, I noted that the copy constructor of flat_buffer does not correctly copies a buffer that had some bytes consumed.

After looking at the source code it seems that the error comes from the flat_buffer::copy_from method: std::memcpy(begin_, other.begin_, n); should probably be std::memcpy(begin_, other.in_, n);

Version of Beast

Version 248 (included in boost 1.70)

Steps necessary to reproduce the problem

#include <iostream>
#include <string>
#include <string_view>

#include <boost/beast/core/flat_buffer.hpp>

int main()
{
	using namespace std;
	using namespace boost::beast;

	const string test_content = "test";

	flat_buffer buf1;
	buf1.commit(
		buffer_copy(
			buf1.prepare(test_content.size()),
			boost::asio::buffer(test_content)));

	buf1.consume(1);

	flat_buffer buf2 = buf1;

	const auto buf1_bytes = buf1.cdata();
	const auto buf2_bytes = buf2.cdata();

	const string_view buf1_sv{
		static_cast<const char*>(buf1_bytes.data()),
		buf1_bytes.size()};

	const string_view buf2_sv{
		static_cast<const char*>(buf2_bytes.data()),
		buf2_bytes.size()};

	cout << "buf1 size     : " << buf1.size() << "\n"
	     << "buf1 contents : " << buf1_sv << "\n"
	     << "buf2 size     : " << buf2.size() << "\n"
	     << "buf2 contents : " << buf2_sv << "\n";

	return 0;
}

prints:

buf1 size     : 3
buf1 contents : est
buf2 size     : 3
buf2 contents : tes

All relevant compiler information

Tested with MSVC 2019.1 and GCC 8.3.0 (linux x64)

[vinniefalco]

Yes it looks like you are correct here, investigating...