How to properly handle decoder chain in netty?

[Jiang Bian]

Frederic -

Always appreciate your quick response.

Yes, I do have those features implemented already, the md5 checksum (i.e. it
might be a overkill, but i just don't want to worry about it), index number
of each chunk, etc.

The protocol works, and the file did go through eventually (of course the
server will request to send the corrupted data again). I just feel annoyed
by the corruption. Now, it seems that I have to live with it.

Thanks again for your help!

Jiang


Frederic Bregier wrote:
> 
> Hi Jiang,
> 
> I think that corrupted data on huge transfer is probably normal.
> 
> My view is based on the following.
> When you want to download a huge file (say a ISO file of your favorite
> linux distribution, about 4 GB), you have often three pointers:
> - one link to an HTTP download link with a "warning" that says "you might
> better want to use the FTP protocol since HTTP download can corrupt data" 
> - one link to an FTP download link
> - one link to a MD5 file with a "warning" saying "for such huge file, you
> should verify the correctness of your download with the following MD5 key"
> 
> So based on this example, my guess is that sending huge file (by chunk or
> not) can lead to some bad transfer that TCP/IP (or even more UDP) cannot
> address.
> That's why most of the "financial" transfer file software integrate a
> checksum during the transfer to validate each file (or even each chunk).
> 
> My suggestion could be the following (but take it only as a suggestion),
> you could perhaps integrate something like a checksum in your protocol, in
> two ways:
> - either at the end of the transfer, you send the checksum (MD5 for
> instance) and compares it on the target host (each checksum computed
> probably at both side during the transfer in order to prevent a new read
> of the file)
> - either for each chunk, you send too a checksum of this chunk to be
> compared on the remote host
> 
> You can even include a count number that orders the chunks (for instance
> to see if there is an error in the transmission where a chunk number 1024
> occurs after a chunk number 1021, meaning the chunks with numbers 1022 and
> 1023 are missing and to enable the restart from chunk 1022).
> 
> But don't go too fast, because including such behaviour in your protocol
> will increase greatly the computation (checksum, order of chunk, retry,
> ...) and so decrease the efficiency. In such problem, it is always a
> choice between efficiency and security, depending on your final goals...
> 
> HTH,
> Frederic
> 
> 

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