LengthFieldBasedFrameDecoder

[Trustin Lee (이희승)]

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
>
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