Re: [Boost-users] [asio] SSL async_shutdown() never finishes if called when async_read_some() is in progress

On 6 April 2018 at 16:29, Alexander D. via Boost-users < boost-users@lists.boost.org> wrote:

On April 6, 2018 9:55 PM, Vinnie Falco via Boost-users < boost-users@lists.boost.org> wrote:

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On Fri, Apr 6, 2018 at 6:11 AM, Alexander D. via Boost-users wrote:

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The only solution I can think of would be to cancel the read operation, but there's no portable way in asio to do this.

sock.next_layer().cancel();

?

Per ASIO Reference:

"Calls to cancel() will always fail with boost::asio::error::operation_not_supported when run on Windows XP, Windows Server 2003, and earlier versions of Windows, unless BOOST_ASIO_ENABLE_CANCELIO is defined. However, the CancelIo function has two issues that should be considered before enabling its use: ..."

which renders cancel() non-portable.

I consider the issues with cancel present in Windows XP and Windows Server 2003 to be sufficiently problematic that it is not worth taking them into account when designing robust network applications (I do develop mostly on Windows). Unless you have a specific business need to support those defective operating systems, I would just ignore them.

Yes, I do need the program to work on at least Windows XP.

However, even if cancel() is used, it is a workaround, not a solution. If you run the code I supplied, you'll notice that async_read_some() is actually finished with a "stream truncated" error, quite similar to "canceling" the read. The problem is on async_shutdown()'s handler not being called, and it's not mentioned anywhere in the reference. Why can't we shutdown a stream while reading from it (since we can close a socket while reading)?

In the past, when I have had queries about the inner workings and design decisions behind ASIO, I have emailed the author, Chris Karloff. I am sure he is a busy guy but he has taken the trouble to answer helpfully in the past. It may be worth dropping him a line and asking for a suggestion. He didn't charge me but having received help twice now, I think it would be rude of me not to offer him a few hours consultancy if I needed his help again. https://think-async.com/Asio/CommercialSupport

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