Socket read problems
dsc at swcp.com
Fri Oct 8 01:42:47 EDT 2010
Could you have gotten the two length bytes swapped and are asking for
way too many bytes?
On Oct 7, 2010, at 6:22 PM, Len Morgan wrote:
> I'm trying to read data from a MODBus/TCP controller and having
> some issues with the timing of the read command. I request a block
> of registers from the slave and it returns the requested bytes and
> header just fine and very quickly. In order to read everything
> right, I have to first read the first 6 bytes of the header to know
> how many bytes are to follow. Once I know that, I do a read from
> socket tSock for <bytes> characters. Note that ALL of the
> characters have been received in a single packet so once I read the
> 6 bytes, the rest of the data is already in the socket buffer.
> The problem I have is when I do the second read, the read command
> blocks for the socketTimeoutInterval before continuing. It doesn't
> matter what I set it to, it will wait that long before continuing.
> I tried catching the socketTimeout message but that message is
> never sent, even when I set the socketTimeoutInterval to 5
> I am not using the read ... with message form of the command since
> I want the handler to wait until all the bytes have been received
> before I move on. Has anyone else seen this? Have I missed
> something in the documentation or could this be something in the
> Windows code that handles sockets?
> Any help would be appreciated!
> len morgan
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