Re: Receiving large text strings with RECV api question

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 18/12/2009, at 9:12 AM, GKern@xxxxxxxxxxxxxxxx wrote:

> Is there any way to trap/detect if a data stream is larger than the  
> what
> the socket's input field can handle?

Only if the data stream is structured and contains a length prefix.  
That's determined at the application level. TCP doesn't know or care.

You need to receive data from the socket until:
	a) Some end-of-data indicator is received
	b) Receiver KNOWS all data is received
	c) EWOULDBLOCK is received on the socket
	d) A timeout occurs on the receive
	e) The sender closes the connexion

a) and b) requires agreement between sender and receiver
c) requires the socket be set to non-blocking mode
d) requires the use of select()


> Can I extract a portion of the data?

You can read it a byte at a time if you like but of course that's less  
efficient. Just read it in chunks of some convenient size.

> I ask that since I've been testing receiving data streams over 32k,  
> but in
> debug the data appears as a string of @'s and I'm not sure what's  
> causing
> that. I'm assuming it's 'error' related.

ASCII @ signs have the same hex representation as EBCDIC spaces (at  
least in the most common US code pages) so it's likely what you're  
seeing is really a bunch of blanks. Note that you can't necessarily  
rely  on that--it's likely the blanks are there as a result of  
initialised storage that hasn't yet had anything written to it. You  
should only process the amount of data that recv() indicates was  
received.

> The numerous things I've tried (including searching the archives and  
> the
> net) have left scratching my head as to how to proceed.
>
> Also I know that QDCXLATE is limited to 32767 bytes. Are there any
> alternatives for translating text larger than 32k or should I just
> deconstruct and then reconstruct it in 32k chunks?

The iconv suite of functions are the preferred way to convert data  
from one CCSID to another.

> At the very least I'd like to be able to detect a large string, pull  
> some
> identifiable data out of it and send off an email to the sender  
> letting
> them know I can't handle data stream larger than x bytes long. Does  
> that
> make sense?

No sense at all. A socket program ought to be able to handle however  
much data is sent to it.

If you must then simply track the number of bytes received from the  
sender and when some arbitrary threshold is reached complain. You'll  
still have to receive the rest of what is sent else it will remain for  
the next receive operation.

Regards,
Simon Coulter.
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