Re: [asio-users] multiple calls of std::ostream( asio::streambuf )

[Christopher K. <ch...@ko...>]

Hi Axel,

On Wed, 31 Jan 2007 11:29:02 +0100, "Alexander (Axel) Straschil"
<ax...@st...> said:
> Hello!
> 
> I'm fooling around with asio falling in love with that ;-)
> 
> Now, if got the following Problem:
> For testing purpose, I'm writing a Webserver just giving the content of a
> File to the Client, the way I did was to read the whole file into an
> asio::streambuf and send this over the socket, works perfectly. 
> Now, as I want to be able to deal with really large files, I want to read
> an
> send chucks of the file, and did something like:
> 
> New Socket Request:
> boost::asio::streambuf out_buffer;
> std::ostream os( out_buffer );
> std::ifstream file( "MyFile.txt", std::ios::in|std::ios::binary );
> char buf[256];
> while ( file.read(buf, sizeof(buf)).gcount() > 0 )
> {        O
>     os.write( buf, file.gcount() );
>     boost::asio::write( socket, out_buffer );
> }
> 
> But this does not write the whole file to the client. 
> On about the first two or three calls. the whole file is written,
> later, only parts are written.
> On each socket request, out_buffer and os is created new.
> 
> Any Idea what I messed up?

The std::ostream object includes a "state" field which can contain
values like badbit, failbit, eofbit etc. If the state has been set it
will no longer perform any I/O. However, the state can be cleared to
allow I/O to proceed again.

I would guess that one of the boost::asio::write() calls is writing all
of the available data in out_buffer, which means that the eofbit state
is getting set. You might try adding the following line inside the loop,
after the call to boost::asio::write():

  os.clear();

Cheers,
Chris