RFC for creation of IntoRaw{Fd, Socket, Handle} trait to complement AsRaw*

Author: ipetkov

text/0000-into-raw-fd-socket-handle-traits.md

@@ -0,0 +1,68 @@
+- Feature Name: into-raw-fd-socket-handle-traits
+- Start Date: 2015-06-24
+- RFC PR:
+- Rust Issue:
+
+# 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.
+
+```rust
+// 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.