Windows Build Broke 0.3.8

[gluax]

Please see the issue describe at tokio-rs/mio#1535.

[Thomasdezeeuw]

@yoshuawuyts @faern could you yank 0.3.8 for now? It contains a breaking change of some kind that broke Mio (see issue linked in original comment).

[yoshuawuyts]

yes, on it! Give me a few mins

[yoshuawuyts]

alright, yanked! Crates.io now resolves to 0.3.7 by default: https://crates.io/crates/miow

[Thomasdezeeuw]

Thanks for the quick response @yoshuawuyts!

[yoshuawuyts]

As to why this released caused build failures, we merged two feature PRs since the last release:

• Mark CompletionStatus as repr(transparent) to guarantee layout #46
• Migrate from winapi to windows-sys #50

I'll have to do some digging to figure out what caused the issue exactly.

[Thomasdezeeuw]

My guess would be the switch to windows-sys reading the logs in tokio-rs/mio#1535 (comment). I think a type from winapi was exposed in Miow's public interface.

[yoshuawuyts]

Ahh, yes I think I might have found the culprit:

• miow::Overlapped::from_raw<'a>(ptr: *mut OVERLAPPED) -> &'a mut Overlapped
• miow::Overlapped::raw(&self) -> *mut OVERLAPPED

Because we switched from winapi to windows-sys, OVERLAPPED comes from a different crate, which leads to issues. Luckily the two definitions are very similar, and going between winapi and windows-sys is likely reasonably straight forward (see next section for an API comparison).

@Thomasdezeeuw what I'm thinking of doing is releasing the current HEAD of miow as 0.4.0. This shouldn't break any existing builds, as it's semver-incompatible. If you like I can then follow that up with a PR to mio to use the latest miow. What do you think?

OVERLAPPED type definitions

Windows Metadata

This is how OVERLAPPED is defined according to microsoft/win32metadata:

public struct OVERLAPPED {
    [StructLayout(LayoutKind.Explicit)]
    public struct _Anonymous_e__Union {
        public struct _Anonymous_e__Struct {
            public uint Offset;
            public uint OffsetHigh;
        }
        [FieldOffset(0)]
        public _Anonymous_e__Struct Anonymous;
        [FieldOffset(0)]
        public unsafe void* Pointer;
    }
    public UIntPtr Internal;
    public UIntPtr InternalHigh;
    public _Anonymous_e__Union Anonymous;
    public HANDLE hEvent;
}

winapi

pub struct OVERLAPPED {
    pub Internal: ULONG_PTR,
    pub InternalHigh: ULONG_PTR,
    pub u: OVERLAPPED_u,
    pub hEvent: HANDLE,
}
pub struct OVERLAPPED_u(_);

windows-sys

pub struct OVERLAPPED {
    pub Internal: usize,
    pub InternalHigh: usize,
    pub Anonymous: OVERLAPPED_0,
    pub hEvent: HANDLE,
}
pub union OVERLAPPED_0 {
    pub Anonymous: OVERLAPPED_0_0,
    pub Pointer: *mut c_void,
}
pub struct OVERLAPPED_0_0 {
    pub Offset: u32,
    pub OffsetHigh: u32,
}

[Thomasdezeeuw]

@Thomasdezeeuw what I'm thinking of doing is releasing the current HEAD of miow as 0.4.0. This shouldn't break any existing builds, as it's semver-incompatible.

I think that makes sense.

If you like I can then follow that up with a PR to mio to use the latest miow. What do you think?

I'll have to review windows-sys crate so that will take me some time. We also use winapi directly, so it might be painful to have both as dependencies. We'll have to see what the best way forward is there.

[Jake-Shadle]

Oops, I didn't see this discussion, but I posted a PR to replace winapi/ntapi in mio just now

• Replace miow, winapi, and ntapi with windows-sys tokio-rs/mio#1556