Hide unnecessary error checking from the user

[tbu-]

This affects the set_non_blocking function which cannot fail for Unix or
Windows, given correct parameters. Additionally, the short UDP write error case
has been removed as there is no such thing as "short UDP writes", instead, the
operating system will error out if the application tries to send a packet
larger than the MTU of the network path.

[rust-highfive]

r? @pcwalton

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[alexcrichton]

What's the motivation for doing this? It seems backwards to explicitly remove this error handling.

[tbu-]

The motivation for this is that the only errors ioctl or ioctlsocket can return are related to misuse of the API (passing in pointer to invalid memory, not passing in a correct fd, ...), and bubbling those up to the user is not useful.

There is also no such thing as a partially sent UDP packet, so if the OS returns that it has been partially sent, something has already gone horribly wrong (see also the commit message).

[oli-obk]

shouldn't this panic in the true-path and leave out the else path instead of unwrapping a fresh Result?

[tbu-]

This should be equivalent and will provide the contents of a potential error.

[oli-obk]

dropping the else-path and calling unwrap() on Err(last_error()) would increase readability imho

[tbu-]

Fixed.

[alexcrichton]

@bors: r+ 0fc1a7d

[Manishearth]

Needs Manishearth@e61a790 ; Manishearth@2470fa1 to compile on windows.

[bors]

⌛ Testing commit 0fc1a7d with merge 2baaabd...

[bors]

💔 Test failed - auto-win-64-opt