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c++socketsiocp

Should I handle the fact that WSASend() may not send all data?

I have found out that WSASend() may not send all of the data, for example if I asked it to send 800 bytes, it may only send 600 bytes.

Now my question is: are the situations where this can happen are extremely rare that I should not bother handling this kind of event. Or do I have to handle it? Can't I for example just show an error message to the user that not all data have been sent and abort the connection instead of trying to recover?

Note: I am using IOCP.

Solution

  • When sending using overlapped I/O and IOCP it's unlikely that you'll ever see a partial send. It's possibly more likely that you'll see a send with an error where you wanted to send a multiple of the system page size and only a smaller multiple was sent, but even that's fairly unlikely (and I don't have unit tests that force that condition as I view it as theoretical).

    When sending via overlapped I/O, over a TCP connection, when your peer is receiving and processing slower than you are sending then this is the more likely situation that you'll encounter, that is, TCP flow control kicking in and your WSASend() calls taking longer and longer to complete.

    It's really unlikely that you'll actually see an error either from a WSASend() call or a subsequent GetQueuedCompletionStatus() call. Things will just keep working until they don't...