Socket::keepalive doesn't work on Windows

[sfackler]

There is apparently not any way of reading these values.

[alexcrichton]

Weird, does the ioctl we execute do anything at all?

And for posterity I think the relevant test which is the impetus for this is here:

https://github.com/alexcrichton/socket2-rs/blob/f1952af36473cbd0934a660fde2f0851c5941033/src/socket.rs#L974-L984

[sfackler]

It fails because the input pointer is invalid.

[yorickpeterse]

I also ran into this issue. When obtaining the keepalive value, an error is returned with the following message:

The system detected an invalid pointer address in attempting to use a pointer argument in a call. (os error 10014)

Unfortunately, I know next to nothing about the winsocks API so I'm not sure how to determine what the root cause is, and how to fix it.

[hawkw]

I did some research, and as far as I can tell, the Microsoft documentation doesn't make any mention of accessing the keepalive values using WSAIoctl, or via any other function. However, it never clearly states that this is not possible.

The closest thing to a definitive answer I could find is this StackOverflow answer (admittedly, not the most reliable source), which states:

The system doesn't have any method of checking the current values of the tcp_keepalive structure passed to WSAIoctl for SIO_KEEPALIVE_VALS. You can set them to the values you want, but you cannot interrogate what they are presently.

Of course, it's still possible to test whether or not keepalive is enabled for a socket on Windows, by using getsockopt(SOL_SOCKET, SO_KEEPALIVE, ...), as one would on Linux. However, it's not possible to retrieve the keepalive time. The only good solution I can think of is splitting the API into two methods, one of which returns a bool indicating whether or not TCP keepalive is enabled, and another which returns the configured keepalive idle duration. The second would have to be #[cfg(not(windows))].