LengthFieldBasedFrameDecoder
Trustin Lee (이희승)
trustin at gmail.com
Thu Sep 24 20:19:57 EDT 2009
Hmm, I want the Javadoc to be easily understandable without referring
to the source code. What would you suggest me to fix the
documentation?
-- Trustin Lee, http://gleamynode.net/
On Wed, Sep 23, 2009 at 3:02 PM, hezjing <hezjing at gmail.com> wrote:
> 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
>> >> 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
>> >
>> >
>>
>> _______________________________________________
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>> netty-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/netty-users
>
>
>
> --
>
> Hez
>
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