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Rename OptionFileHandle to HandleOrInvalid and make it just wrap an Option<OwnedHandle>
The name (and updated documentation) make the FFI-only usage clearer, and wrapping Option<OwnedHandle> avoids the need to write a separate Drop or Debug impl. Co-authored-by: Josh Triplett <josh@joshtriplett.org>
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@ -45,7 +45,7 @@ pub struct BorrowedHandle<'handle> {
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/// Note that it *may* have the value `INVALID_HANDLE_VALUE` (-1), which is
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/// sometimes a valid handle value. See [here] for the full story. For APIs
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/// like `CreateFileW` which report errors with `INVALID_HANDLE_VALUE` instead
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/// of null, use [`OptionFileHandle`] instead of `Option<OwnedHandle>`.
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/// of null, use [`HandleOrInvalid`] instead of `Option<OwnedHandle>`.
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///
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/// `OwnedHandle` uses [`CloseHandle`] to close its handle on drop. As such,
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/// it must not be used with handles to open registry keys which need to be
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@ -61,25 +61,21 @@ pub struct OwnedHandle {
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handle: NonNull<c_void>,
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}
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/// Similar to `Option<OwnedHandle>`, but intended for use in FFI interfaces
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/// where `INVALID_HANDLE_VALUE` is used as the sentry value, and null values
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/// are not used at all, such as in the return value of `CreateFileW`.
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/// FFI type for handles in return values or out parameters, where `INVALID_HANDLE_VALUE` is used
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/// as a sentry value to indicate errors, such as in the return value of `CreateFileW`. This uses
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/// `repr(transparent)` and has the representation of a host handle, so that it can be used in such
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/// FFI declarations.
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///
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/// The main thing you can do with an `OptionFileHandle` is to convert it into
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/// an `OwnedHandle` using its [`TryFrom`] implementation, and this conversion
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/// takes care of the check for `INVALID_HANDLE_VALUE`.
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/// The only thing you can usefully do with a `HandleOrInvalid` is to convert it into an
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/// `OwnedHandle` using its [`TryFrom`] implementation; this conversion takes care of the check for
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/// `INVALID_HANDLE_VALUE`. This ensures that such FFI calls cannot start using the handle without
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/// checking for `INVALID_HANDLE_VALUE` first.
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///
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/// If this holds an owned handle, it closes the handle on drop.
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///
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/// This uses `repr(transparent)` and has the representation of a host handle,
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/// so it can be used in FFI in places where a non-null handle is passed as a
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/// consumed argument or returned as an owned value, or it is
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/// `INVALID_HANDLE_VALUE` indicating an error or an otherwise absent value.
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/// If this holds a valid handle, it will close the handle on drop.
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#[repr(transparent)]
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#[unstable(feature = "io_safety", issue = "87074")]
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pub struct OptionFileHandle {
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handle: RawHandle,
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}
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#[derive(Debug)]
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pub struct HandleOrInvalid(Option<OwnedHandle>);
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// The Windows [`HANDLE`] type may be transferred across and shared between
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// thread boundaries (despite containing a `*mut void`, which in general isn't
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@ -87,10 +83,10 @@ pub struct OptionFileHandle {
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//
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// [`HANDLE`]: std::os::windows::raw::HANDLE
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unsafe impl Send for OwnedHandle {}
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unsafe impl Send for OptionFileHandle {}
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unsafe impl Send for HandleOrInvalid {}
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unsafe impl Send for BorrowedHandle<'_> {}
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unsafe impl Sync for OwnedHandle {}
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unsafe impl Sync for OptionFileHandle {}
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unsafe impl Sync for HandleOrInvalid {}
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unsafe impl Sync for BorrowedHandle<'_> {}
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impl BorrowedHandle<'_> {
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@ -114,54 +110,31 @@ impl BorrowedHandle<'_> {
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}
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}
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impl OptionFileHandle {
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/// Return an empty `OptionFileHandle` with no resource.
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#[inline]
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#[unstable(feature = "io_safety", issue = "87074")]
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pub const fn none() -> Self {
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Self { handle: c::INVALID_HANDLE_VALUE }
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}
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}
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impl TryFrom<OptionFileHandle> for OwnedHandle {
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impl TryFrom<HandleOrInvalid> for OwnedHandle {
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type Error = ();
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#[inline]
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fn try_from(option: OptionFileHandle) -> Result<Self, ()> {
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let handle = option.handle;
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forget(option);
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if let Some(non_null) = NonNull::new(handle) {
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if non_null.as_ptr() != c::INVALID_HANDLE_VALUE {
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Ok(Self { handle: non_null })
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} else {
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Err(())
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}
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fn try_from(handle_or_invalid: HandleOrInvalid) -> Result<Self, ()> {
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// In theory, we ought to be able to assume that the pointer here is
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// never null, use `OwnedHandle` rather than `Option<OwnedHandle>`, and
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// obviate the the panic path here. Unfortunately, Win32 documentation
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// doesn't explicitly guarantee this anywhere.
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//
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// APIs like [`CreateFileW`] itself have `HANDLE` arguments where a
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// null handle indicates an absent value, which wouldn't work if null
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// were a valid handle value, so it seems very unlikely that it could
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// ever return null. But who knows?
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//
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// [`CreateFileW`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
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let owned_handle = handle_or_invalid.0.expect("A `HandleOrInvalid` was null!");
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if owned_handle.handle.as_ptr() == c::INVALID_HANDLE_VALUE {
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Err(())
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} else {
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// In theory, we ought to be able to assume that the pointer here
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// is never null, change `option.handle` to `NonNull`, and obviate
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// the the panic path here. Unfortunately, Win32 documentation
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// doesn't explicitly guarantee this anywhere.
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//
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// APIs like [`CreateFileW`] itself have `HANDLE` arguments where a
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// null handle indicates an absent value, which wouldn't work if
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// null were a valid handle value, so it seems very unlikely that
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// it could ever return null. But who knows?
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//
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// [`CreateFileW`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
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panic!("An `OptionFileHandle` was null!");
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Ok(owned_handle)
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}
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}
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}
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impl From<OwnedHandle> for OptionFileHandle {
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#[inline]
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fn from(owned: OwnedHandle) -> Self {
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let handle = owned.handle;
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forget(owned);
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Self { handle: handle.as_ptr() }
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}
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}
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impl AsRawHandle for BorrowedHandle<'_> {
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#[inline]
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fn as_raw_handle(&self) -> RawHandle {
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@ -188,7 +161,7 @@ impl IntoRawHandle for OwnedHandle {
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impl FromRawHandle for OwnedHandle {
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/// Constructs a new instance of `Self` from the given raw handle.
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///
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/// Use `OptionFileHandle` instead of `Option<OwnedHandle>` for APIs that
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/// Use `HandleOrInvalid` instead of `Option<OwnedHandle>` for APIs that
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/// use `INVALID_HANDLE_VALUE` to indicate failure.
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///
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/// # Safety
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@ -212,12 +185,12 @@ impl FromRawHandle for OwnedHandle {
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}
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}
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impl FromRawHandle for OptionFileHandle {
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/// Constructs a new instance of `Self` from the given raw handle returned
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impl FromRawHandle for HandleOrInvalid {
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/// Constructs a new instance of `Self` from the given `RawHandle` returned
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/// from a Windows API that uses `INVALID_HANDLE_VALUE` to indicate
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/// failure, such as `CreateFileW`.
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///
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/// Use `Option<OwnedHandle>` instead of `OptionFileHandle` for APIs that
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/// Use `Option<OwnedHandle>` instead of `HandleOrInvalid` for APIs that
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/// use null to indicate failure.
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///
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/// # Safety
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@ -230,8 +203,8 @@ impl FromRawHandle for OptionFileHandle {
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/// [here]: https://devblogs.microsoft.com/oldnewthing/20040302-00/?p=40443
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#[inline]
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unsafe fn from_raw_handle(handle: RawHandle) -> Self {
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assert!(!handle.is_null());
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Self { handle }
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// We require non-null here to catch errors earlier.
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Self(Some(OwnedHandle::from_raw_handle(handle)))
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}
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}
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@ -244,15 +217,6 @@ impl Drop for OwnedHandle {
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}
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}
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impl Drop for OptionFileHandle {
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#[inline]
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fn drop(&mut self) {
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unsafe {
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let _ = c::CloseHandle(self.handle);
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}
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}
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}
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impl fmt::Debug for BorrowedHandle<'_> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("BorrowedHandle").field("handle", &self.handle).finish()
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@ -265,12 +229,6 @@ impl fmt::Debug for OwnedHandle {
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}
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}
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impl fmt::Debug for OptionFileHandle {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("OptionFileHandle").field("handle", &self.handle).finish()
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}
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}
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/// A trait to borrow the handle from an underlying object.
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#[unstable(feature = "io_safety", issue = "87074")]
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pub trait AsHandle {
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@ -34,7 +34,7 @@ pub mod prelude {
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use super::io::{
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AsHandle, AsSocket, BorrowedHandle, BorrowedSocket, FromRawHandle, FromRawSocket,
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IntoRawHandle, IntoRawSocket, OptionFileHandle, OwnedHandle, OwnedSocket,
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HandleOrInvalid, IntoRawHandle, IntoRawSocket, OwnedHandle, OwnedSocket,
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};
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#[doc(no_inline)]
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#[stable(feature = "rust1", since = "1.0.0")]
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