Re: [Boost-users] [Asio] async_read_until is passing no error and bytes_transferred of zero to handler

Subject: Re: [Boost-users] [Asio] async_read_until is passing no error and bytes_transferred of zero to handler
From: Marcano, Gabriel E (gmarcano_at_[hidden])
Date: 2014-05-08 13:31:58

> Ok, my last suggestion is to set num_threads=1 when constructing the 
> io_service.

This worked for the first time I ran the tests... but the second time the
problem resurfaced. What baffles me is that none of the other serial
applications on my computer seem to be dropping bytes...

> Just because it may have worked on an older ASIO means little.

I actually haven't tried any other version of ASIO with this code. It may
or may not have worked before.

> An boss of mine said "never use any serial API not used by
> HyperTerminal" and I think he was right.

I'm beginning to think this myself, and further, this could probably be
generalized for a lot of more proprietary programming APIs... at least
based on my limited experience thus far.

Still, I am not sure the problem lies with the serial code alone.
async_read_until's behavior does not conform to its documentation-- that
is certainly a bug. This is from the Boost.Asio async_read_until docs:

    Parameters:
    ...
        void handler(
          // Result of operation.
          const boost::system::error_code& error,

          // The number of bytes in the streambuf's get
          // area up to and including the delimiter.
          // 0 if an error occurred.
          std::size_t bytes_transferred
        );
        
If I'm interpreting this correctly, error and bytes_transferred cannot be
errorless and 0, respectively. This is exactly the behavior I'm observing.
The question is, I guess, what is causing this. Like you said, it could
very well be a bug in Windows that is leaking through the Boost.Asio
implementation of async_read_until. Regardless of whose fault it is,
currently async_read_until does not conform to its documentation. I'll
keep probing at it as work permits, but I'm unfamiliar with most of
Windows's APIs so I have my doubts that I'll be able to trace the problem.
Thanks for the help!