[Qt-interest] Fwd: Network file transfer

[Shantanu Tushar Jha]

Oops, i forgot to cc the mailing list.

On Thu, Aug 27, 2009 at 10:16 PM, Jeroen De Wachter <
jeroen.dewachter at barco.com> wrote:

> QTcpSocket (and, in fact, the OS) should take care of splitting up the
> transfer into smaller packets.
> There is no 64K limitation mentioned in QTcpSocket's implementation in
> any case.
>
> Shantanu:
>
> About: socket.write(file.read(100000));
>
> Do you check the return status of the write call on QTcpSocket? If it
> returns -1, there's been an error. This is an often overlooked
> mistake...


yes, it returns 100000 only.

>
> You should also check the return status on the read call you are doing,
> by the way, don't just assume it's completed OK. Check the error()
> command on your QFile if the read call returns an empty QByteArray.
>
> I would also suggest just sending the file in its entirety without
> sending SENDDATA messages in the "control" channel to regulate the flow
> of data.
> It's of course fine to buffer only a certain amount of data in the
> thread (don't put 2 gigabyte files entirely into memory, for instance),
> but there is no reason to communicate between client and server to
> notify the client that 100000 bytes are coming...
>
> Don't worry about making sure the bytes get there, the TCP protocol is
> designed to be reliable and (in my experience) usually does its job
> rather well. Just remember to take into account the return values of the
> methods you call on the files/sockets.


Then should i just keep executing socket.write(data) (where data is some
100000 bytes) in a loop until whole file is transferred ?
just for info, this is for a LAN, so no speed problems.

>
>
> Kind regards,
>
> Jeroen
>
> On Thu, 2009-08-27 at 19:36 +0400, Constantin Makshin wrote:
> > TCP window size is specified by 2 bytes in the TCP packet header, so the
> > limit is 64KB. Try sending files in smaller chunks.
> >
> > On Thu, 27 Aug 2009 13:24:53 +0400, Shantanu Tushar Jha
> > <jhahoneyk at gmail.com> wrote:
> > > Hello all,
> > > I want to transfer files (small to huge) over the network using Qt 4.5
> > >
> > > Right now, i'm making use of the following steps-
> > > 1. Client (QTcpSocket) sends filename to the server (QTcpServer)
> > > 2. server creates a thread each "incomingConnection" and the thread
> sends
> > > "OK<filesize>" if file was found.
> > > 3. client receives "OK<filesize>" and sends "SENDDATA" to server
> > > 4. server receives "SENDDATA" and sends first 100,000 (100KB) of data
> to
> > > the client.    ( using socket.write(file.read(100000)) )
> > > 5. client gets the data and saves it to a file. then it sends
> "SENDDATA"
> > > to server    ( using file.write(socket.readAll()) )
> > > 6. server receives "SENDDATA" and sends next 100,000 (100KB) of data to
> > > the client, and so on ....
> > > 7. client stops after <filesize> bytes have been written
> > >
> > > Now, this seems to work randomly sometimes, and at times creating
> corrupt
> > > transfers. The problem is that the server does send 100000 bytes, but
> at
> > > times the client receives less than that (i've added to wait till
> > > socket.bytesAvailable() >= 100000 but that never happens in the case).
> > > Any ideas?
> > >
> > > Also, to send the file data, i'm right now using
> > > socket.write(file.read(100000)); and for the status strings (e.g. OK)
> i'm
> > > using socket.write(string.toUtf8());
> > > Should I use QDataStream here ?
> > >
> > > Thanks a lot :)
> >
>
>
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-- 
Shantanu Tushar    (UTC +0530)
http://www.shantanutushar.com



-- 
Shantanu Tushar    (UTC +0530)
http://www.shantanutushar.com
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