Re: [boost] [asio] buffered_read_stream issue, with async_read()

Subject: Re: [boost] [asio] buffered_read_stream issue, with async_read()
From: Michael Caisse (boost_at_[hidden])
Date: 2009-06-04 16:04:10

brad higgins wrote:
> Hi,
>   I am using boost asio in a project.  My program has  a TCP protocol 
> which reads a fixed size message header, followed by a variable-sized 
> message body.  It is possible to have a message with a 0-byte body, 
> and it is possible that no messages are received for some time.
>
>   I have an issue when attempting to async_read() a 0-byte body with 
> the buffered_read_stream, detailed here:
>
> (1) My program reads a fixed-sized header
> (2) After this succeeds, my program issues an async read for 0 bytes, 
> for the message body
> (3) buffered_read_stream sees that storage_ is empty, so it calls 
> async_fill(), to fill it
> (4) no more messages arrive for some time, so there is no data 
> available to fill
> (5) BUG -> My program's 0-byte read timer expires, rather than the 
> read() succeeding and calling my handler immediately
>
>   If I use the boost::asio::tcp::socket instead of the 
> buffered_read_stream, the 0-byte read occurs immediately, and does not 
> time out.  I believe the read() with the buffered_read_stream is 
> getting 'blocked' in async_fill(), rather than succeeding immediately.
>
>   Do you think the buffered_read_stream should have special cases for 
> 0 byte reads to cover this case, or do you think client code should 
> avoid issuing 0 byte reads?
>
> Thanks,
> Brad
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Brad -

Perhaps you can consider changing your completion routine for the header
read. If the header indicates that the body is 0 bytes then there
is no need to read a body. Simply read the next header.

I have a similar setup for some of servers.

Best Regards -
michael

-- 
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Michael Caisse
Object Modeling Designs
www.objectmodelingdesigns.com