garbled data passed in cumulation buffer for decode(), probably when data re-transmission.

[huican ping]

Hello Trustin,

I have been looking at that garbled channel buffer for my FrameDecoder
case in these days.
FYI, my dummy frameDecoder for comming message with structure (for
example): StartByte+Any-Bytes-Different-Than-StartByte-Trailer+TrailerByte.

So far, I saw both the two failed cases for my 1066 bytes (results in
2 messageReceived calls).
  a) good-1024-bytes + bad data.   // Since I am waiting on the tailer
byte, so it receiveTimeout.
  b) bad-1024-bytes + good data.   // Since I found the trailer byte,
but there is no good startByte, so it is bad message.

1:) I captured and tcpdumped one failed case inside
million-and-million successful oens, and noticed that the client sent
in a good message to the server based on the FrameDecoder.
2:) and when I read the code at: FrameDecoder.java, method messageReceived().
Since the client can sends in a message which results in multiple
messageReceived Call (such as 2 for my input), I just wonder how the
code below to keep synchronizing the cumulation buffer for these if
and else cases. What I am worrying is that when the previous
messageReceived event at the else branch (not done yet), another
messageReceived event can go into the if branch.

Is this a problem?

Thanks
Huican Ping

===============
    public void messageReceived(
            ChannelHandlerContext ctx, MessageEvent e) throws Exception {

        Object m = e.getMessage();
        if (!(m instanceof ChannelBuffer)) {
            ctx.sendUpstream(e);
            return;
        }

        ChannelBuffer input = (ChannelBuffer) m;
        if (!input.readable()) {
            return;
        }

        ChannelBuffer cumulation = cumulation(ctx);
        if (cumulation.readable()) {
            cumulation.discardReadBytes();
            cumulation.writeBytes(input);
            callDecode(ctx, e.getChannel(), cumulation, e.getRemoteAddress());
        } else {
            callDecode(ctx, e.getChannel(), input, e.getRemoteAddress());
            if (input.readable()) {
                cumulation.writeBytes(input);
            }
        }
    }
==========================



On Thu, Sep 10, 2009 at 10:17 PM, huican ping <pinghuican at gmail.com> wrote:
> Hello Trustin,
>
> I thought I found some place in my parser suspicious, now my logic is
> pretty much same as the example posted at the FrameDecoder page, and
> still get the same issue.
>
> // My decode() logic.
> protected Object decode(ChannelHandlerContext ctx, Channel channel,
>                        ChannelBuffer buffer) throws Exception {
>
>        // return if the buffer empty
>        if (buffer.readableBytes() <= 0) {
>                return null;
>        }
>
>        // Mark the current buffer position before parsing the buffer
>        // because the whole message might not be in the buffer yet.
>        // We will reset the buffer position to the marked position in
>        // that case.
>        buffer.markReaderIndex();
>
>
>        for ( loc = buffer.readerIndex(); loc < buffer.writerIndex(); loc++)
>        {
>                // Paser code.
>                // if find the whole message, then return that message
>                // otherwise, it will hit the end of the loop
>                // Inside the loop
>
>                // I didn't modify the buffer except change its readerIndex if
>                // the whole message is not there yet.
>        }
>
>
>        // The whole message were not received yet - return null.
>        // This method will be invoked again when more packets are
>        // received and appended to the buffer.
>
>        // Reset to the marked position to read the length field again
>        // next time.
>        buffer.resetReaderIndex();
>        return null;
> }
>
> // my getPipeline() logic:
>                pipeline.addLast("decoder", new acmeDecoder());
>                pipeline.addLast("encoder", new acmeEncoder());
>                pipeline.addLast("handler", new acmeServerHandler());
>
>
> Thanks
> Huican Ping
>
> On Thu, Sep 10, 2009 at 9:49 PM, Huican Ping <pinghuican at gmail.com> wrote:
>>
>> Hello Trustin,
>>
>> Probably it is my parser problem. Don't waste time on it now. I am
>> sorry about it.
>>
>> Thanks
>> Huican Ping
>>
>> On Thu, Sep 10, 2009 at 5:40 PM, Huican Ping (via Nabble)
>> <ml-user+135163-919750110 at n2.nabble.com> wrote:
>>> FYI, my decoder inherited from the FrameDecoder.
>>>
>>> Thanks
>>> Huican Ping
>