Conversion of ChannelBuffer to InputStream

[이희승 (Trustin Lee)]

Hi Mike,

On Fri, 21 Aug 2009 03:10:42 +0900 (KST)
MikeQ <michaelquilleash at hotmail.com> wrote:

> 
> Hi all,
> 
> I am looking at using Netty for the first time.  I am trying to build
> a simple server that when a message is received a method of the form 
> 
> handleRequest( InputStream inputStream, OutputStream )
> 
> I'm not quite sure how to implement the InputStream part of this.  I
> want the called code to "pull" data off the InputStream as and when
> it chooses to rather than a callback handler pushing data
> continually.  (You could liken it to comparing SAX with StAX in XML
> world).
> 
> I looked at the decoder/framing stuff but I don't want to buffer the
> whole request in memory first as it may be very large, want to stream
> it off the network as it arrives.  Similar for the response.
> 
> Is there a common/suitable method for making this conversion?  It
> seems that I need something like the following.
> 
> - create an InputStream backed by some custom buffer
> - on messageReceived() callback copy ChannelBuffer contents into the
> custom buffer
> - invoke the method with the InputStream
> - the first messageReceived() may not contain all the data so
> subsequent calls would need to push the new data behind the same
> InputStream to be consumed by the client if necessary
> - when the called code is finished it returns
> - if there is still data buffered then the method is invoked again
> - repeat until data buffer is empty, go back to waiting for a new
> messageReceived() call
> 
> Is there anything out there that does the above?  Or should I just
> write something from scratch?

You might want to use something like PipeInput/OutputStream combo and
copy the content of the received ChannelBuffer to the PipeOutputStream
so that your 'handleRequest' method reads the data from
PipeInputStream.

To write the content of a ChannelBuffer to an OutputStream, you could
call ChannelBuffer.readBytes(OutputStream, ...).

> If I need to write from scratch are there any recommendations?
> 
> - Can I just copy the ChannelBuffer references on each callback and
> queue them somewhere?  Or do I need to drain the contents to a
> separate buffer before messageReceived() returns?

You don't need to drain the content of the received buffer.  Netty
I/O thread does not reuse nor modify the content of the buffer once it
fires a messageReceived event.  Therefore, you can keep the buffer
reference as you like.

> - Do I need to use a OrderedMemoryAwareThreadPoolExecutor somewhere?
> If so where?

I'd place it before handing off the buffer to the blocking stream so
that other connections are not blocked by the blocking I/O in your code.

HTH,
Trustin