Summary

Introduce and implement IntoRaw{Fd, Socket, Handle} traits to complement the existing AsRaw{Fd, Socket, Handle} traits already in the standard library.

Motivation

The FromRaw{Fd, Socket, Handle} traits each take ownership of the provided handle, however, the AsRaw{Fd, Socket, Handle} traits do not give up ownership. Thus, converting from one handle wrapper to another (for example converting an open fs::File to a process::Stdio) requires the caller to either manually dup the handle, or mem::forget the wrapper, which is unergonomic and can be prone to mistakes.

Traits such as IntoRaw{Fd, Socket, Handle} will allow for easily transferring ownership of OS handles, and it will allow wrappers to perform any cleanup/setup as they find necessary.

Detailed design

The IntoRaw{Fd, Socket, Handle} traits will behave exactly like their AsRaw{Fd, Socket, Handle} counterparts, except they will consume the wrapper before transferring ownership of the handle.

Note that these traits should not have a blanket implementation over T: AsRaw{Fd, Socket, Handle}: these traits should be opt-in so that implementors can decide if leaking through mem::forget is acceptable or another course of action is required.

// Unix
pub trait IntoRawFd {
    fn into_raw_fd(self) -> RawFd;
}

// Windows
pub trait IntoRawSocket {
    fn into_raw_socket(self) -> RawSocket;
}

// Windows
pub trait IntoRawHandle {
    fn into_raw_handle(self) -> RawHandle;
}

Drawbacks

This adds three new traits and methods which would have to be maintained.

Alternatives

Instead of defining three new traits we could instead use the std::convert::Into<T> trait over the different OS handles. However, this approach will not offer a duality between methods such as as_raw_fd()/into_raw_fd(), but will instead be as_raw_fd()/into().

Another possibility is defining both the newly proposed traits as well as the Into<T> trait over the OS handles letting the caller choose what they prefer.

Unresolved questions

None at the moment.

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