Hello,

This UDP stuff is driving me nuts.
Maximum outbound (send) size of a message returned by getsockopt
as described below is 65507 bytes on my w2k box. Up to this size
datagrams go over the wire. However if I SendTo a bigger datagram
up to 65527 bytes then SendTo happily returns success even though
nothing was sent! At a datagram size of 65528 bytes however the
function fails with WSAGetLastError returning WSAEMSGSIZE as
stated in the M$ documentation, is this normal? 

Also, when I set the IP_DONTFRAGMENT flag before sending a datagram
that would have being fragmented otherwise SendTo also happily
returns success even though no data was sent.

---
Arno Garrels [TeamICS]
http://www.overbyte.be/eng/overbyte/teamics.html



Arno Garrels wrote:
> Hello,
> 
> I would like to send datagrams thru SendTo() instead of
> Send() in order to bypass copying data to TWSocket's send
> buffer. When I call SendTo() I have to handle
> possible errors by myself, but I do not understand
> exactely whether it's possible that the function returns
> a positive result smaller than Len.
> 
> The online help says:
> 
> "If no error occurs, sendto returns the total number of bytes
> sent, which can be less than the number indicated by len."
> 
> OK, but a little bit later:
> 
> "For message-oriented sockets, care must be taken not to exceed
> the maximum packet size of the underlying subnets, which can
> be obtained by using getsockopt to retrieve the value of
> socket option SO_MAX_MSG_SIZE. If the data is too long to pass
> atomically through the underlying protocol, the error
> WSAEMSGSIZE is returned and no data is transmitted."
> 
> Does this mean that in UDP either any number of bytes is sent
> or WSAEMSGSIZE is returned?
> 
> 
> ---
> Arno Garrels [TeamICS]
> http://www.overbyte.be/eng/overbyte/teamics.html
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