LengthFieldBasedFrameDecoder
hezjing
hezjing at gmail.com
Wed Sep 23 02:02:37 EDT 2009
Yes, you're right.
I should really create a decoder with LengthFieldBasedFrameDecoder(0xFFFF,
2, 2, 16, 0).
I was having problem figuring the correct lengthAdjustment until I found the
formula from the LengthFieldBasedFrameDecoder source code:
frameLength += lengthAdjustment + lengthFieldEndOffset;
Again, thanks for your help!
On Mon, Sep 21, 2009 at 2:45 PM, Trustin Lee (이희승) <trustin at gmail.com>wrote:
> Not actually. It is supposed to work with either cases, as there are
> lengthAdjustment and initialBytesToStrip.
>
> initialBytesToStrip should be 0 because you don't want the resulting
> frame's header stripped out.
>
> lengthAdjustment could be 20 or something close to it because there's
> an extra data between the length field and the payload.
>
> The Javadoc says:
>
> "It is particularly useful when you decode a binary message which has
> an integer header field that represents the length of the message body
> or the whole message."
>
> which means, it works regardless whether the length field includes the
> header or not. Am I missing something? Could you suggest where to
> improve?
>
> — Trustin Lee, http://gleamynode.net/
>
>
>
> On Mon, Sep 21, 2009 at 3:24 PM, hezjing <hezjing at gmail.com> wrote:
> > Hi Trustin
> >
> > In my case, the length field is the size of the payload (excluding the
> > header).
> >
> > If I read the Javadoc correctly, the LengthFieldBasedFrameDecoder is
> > applicable when the length field is the size of the header and payload
> > right?
> >
> > :-)
> >
> > On Mon, Sep 21, 2009 at 9:39 AM, Trustin Lee (이희승) <trustin at gmail.com>
> > wrote:
> >>
> >> Hi Hez,
> >>
> >> Thanks for closing this thread with a good answer and sorry that I'm
> late.
> >>
> >> Do you find the Javadoc of LengthFieldBasedFrameDecoder difficult to
> >> understand? I thought your use case is explained already there. Let
> >> me know what you think so that we can improve the documentation.
> >>
> >> Cheers
> >>
> >> — Trustin Lee, http://gleamynode.net/
> >>
> >>
> >>
> >> On Sun, Sep 20, 2009 at 9:12 PM, hezjing <hezjing at gmail.com> wrote:
> >> > Hi Mike
> >> > Hmmm ... do you mean the example of the frame like the following?
> >> > <-- HEADER 20 bytes --><-- PAYLOAD 14 bytes -->
> >> > +-------+---------+----+-----------------------+
> >> > | | Length | | Payload |
> >> > | | 0x000C | | |
> >> > +-------+---------+----+-----------------------+
> >> > Total frame size is 34 bytes.
> >> > <-- HEADER 20 bytes --><-- PAYLOAD 100 bytes -->
> >> > +-------+--------+-----+------------------------+
> >> > | | Length | | Payload |
> >> > | | 0x0064 | | |
> >> > +-------+--------+-----+------------------------+
> >> > Total frame size is 120 bytes.
> >> >
> >> >
> >> > On Sun, Sep 20, 2009 at 1:41 AM, Mike McGrady
> >> > <mmcgrady at topiatechnology.com>
> >> > wrote:
> >> >>
> >> >> Could you include an example write with this? The two together, I
> >> >> suspect, will be most helpful to many people, including me.
> >> >> Mike
> >> >> On Sep 19, 2009, at 8:11 AM, hezjing wrote:
> >> >>
> >> >> Hi
> >> >> To close this thread, my solution is to extends FrameDecoder like the
> >> >> following code:
> >> >> @ChannelPipelineCoverage("all")
> >> >> public class MyFrameDecoder extends FrameDecoder {
> >> >> @Override
> >> >> protected Object decode(ChannelHandlerContext ctx, Channel
> channel,
> >> >> ChannelBuffer buf) throws Exception {
> >> >> // the length field is at 3rd and 4th octet
> >> >> if (buf.readableBytes() < 4) {
> >> >> return null;
> >> >> }
> >> >> // The length field is in the buffer.
> >> >> buf.markReaderIndex();
> >> >> ...
> >> >> // Read the length field (the payload size)
> >> >> int length = buf.readUnsignedShort();
> >> >> // The actual frame size is header (20) + payload size
> >> >> length += 20;
> >> >> buf.resetReaderIndex();
> >> >> if (buf.readableBytes() < length) {
> >> >> return null;
> >> >> }
> >> >> ChannelBuffer frame = buf.readBytes(length);
> >> >> return frame;
> >> >> }
> >> >> }
> >> >>
> >> >> Thank you!
> >> >>
> >> >> On Thu, Sep 10, 2009 at 9:23 PM, hezjing <hezjing at gmail.com> wrote:
> >> >>>
> >> >>> Hi
> >> >>> I have a message containing a fixed length header of 20 bytes,
> >> >>> followed
> >> >>> by a payload of variable length.
> >> >>> The header contains a 2 bytes length field, indicating the length of
> >> >>> the
> >> >>> payload (excluding the header).
> >> >>> For example if the message has 10 bytes payload, then the entire
> frame
> >> >>> length is 30 bytes (20 bytes header + 10 bytes of payload),
> >> >>> and the length field is 10.
> >> >>> May I know what is the parameter to
> >> >>> create LengthFieldBasedFrameDecoder?
> >> >>>
> >> >>> Thank you!
> >> >>>
> >> >>> --
> >> >>>
> >> >>> Hez
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >>
> >> >> Hez
> >> >> _______________________________________________
> >> >> netty-users mailing list
> >> >> netty-users at lists.jboss.org
> >> >> https://lists.jboss.org/mailman/listinfo/netty-users
> >> >>
> >> >> Mike McGrady
> >> >> Principal Investigator AF081-028 AFRL SBIR
> >> >> Senior Engineer
> >> >> Topia Technology, Inc.
> >> >> 1.253.720.3365
> >> >> mmcgrady at topiatechnology.com
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> netty-users mailing list
> >> >> netty-users at lists.jboss.org
> >> >> https://lists.jboss.org/mailman/listinfo/netty-users
> >> >>
> >> >
> >> >
> >> >
> >> > --
> >> >
> >> > Hez
> >> >
> >> > _______________________________________________
> >> > netty-users mailing list
> >> > netty-users at lists.jboss.org
> >> > https://lists.jboss.org/mailman/listinfo/netty-users
> >> >
> >> >
> >>
> >> _______________________________________________
> >> netty-users mailing list
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> >> https://lists.jboss.org/mailman/listinfo/netty-users
> >
> >
> >
> > --
> >
> > Hez
> >
> > _______________________________________________
> > netty-users mailing list
> > netty-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/netty-users
> >
> >
>
> _______________________________________________
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--
Hez
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