IOCP server and send data with single wsasend

Question

I work on IOCP Server in windows. And i have to send buffer to all connected socket. The buffer size is small - up to 10 bytes. When i get notification for each wsasend in GetQueuedCompletionStatus, is there guarantee that the buffer was sent in one piece by single wsasend? Or should i put additional code, that check if all 10 bytes was sent, and post another wsasend if necessary?

Answer 1

There is no guarantee but it's highly unlikely that a send that is less than a single operating system page size would partially fail.

Failures are more likely if you're sending a buffer that is more than a single operating system page size in length and if you're not actively managing how many outstanding operations you have and how many your system can support before running out of "non paged pool" or hitting the "I/O page lock limit"

It's only possible to recover from a partial failure if you never have any other sends pending on that connection.

I tend to check that the value is as expected in the completion handler and abort the connection with an RST if it's not. I've never had this code execute in production and I've been building lots of different kinds of IOCP based client and server systems for well over 10 years now.