C++ boost asio Windows file handle async_read_until infinite loop - no eof

Question

I\'m using boost 1.50 with VS2010, reading using a Windows file HANDLE (which seems to be relatively uncommon compared to asio use with sockets).

Probl

Answer 1

A stream_handle will always read at offset zero. I think it's meant for sockets handles and useless for regular files.

Calling async_read_until() gets 512 bytes if the streambuf doesn't already contain a newline. The first call reads a bit more than 7 lines. When seven lines are extracted the remainig characters ("LINE 8 abcdefghijklmno") don't have a newline and (the same) 512 bytes are appended.

To solve the problem I'd suggest to use a random_access_handle. You have to track the file position manually and replace async_read_until with async_read_at.

class AsyncReader
{
  ...
  void start_read()
  {
    async_read_at(input_handle, input_offset, input_buffer, ...);
  }
private:
  boost::asio::windows::random_access_handle input_handle;
  boost::uint64_t input_offset;
};

void AsyncReader::handle_read(const boost::system::error_code& error,
                              std::size_t length)
{
  input_offset += length;
  if (!error || error == boost::asio::error::eof)
  {
    ...