1 files changed, 172 insertions, 0 deletions
diff --git a/src/win.rs b/src/win.rs
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index 0000000..6924739
--- /dev/null
+++ b/src/win.rs
@@ -0,0 +1,172 @@
+use std::fs::File;
+use std::hash::{Hash, Hasher};
+use std::io;
+use std::os::windows::io::{AsRawHandle, IntoRawHandle, RawHandle};
+use std::path::Path;
+
+use winapi_util as winutil;
+
+// For correctness, it is critical that both file handles remain open while
+// their attributes are checked for equality. In particular, the file index
+// numbers on a Windows stat object are not guaranteed to remain stable over
+// time.
+//
+// See the docs and remarks on MSDN:
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa363788(v=vs.85).aspx
+//
+// It gets worse. It appears that the index numbers are not always
+// guaranteed to be unique. Namely, ReFS uses 128 bit numbers for unique
+// identifiers. This requires a distinct syscall to get `FILE_ID_INFO`
+// documented here:
+// https://msdn.microsoft.com/en-us/library/windows/desktop/hh802691(v=vs.85).aspx
+//
+// It seems straight-forward enough to modify this code to use
+// `FILE_ID_INFO` when available (minimum Windows Server 2012), but I don't
+// have access to such Windows machines.
+//
+// Two notes.
+//
+// 1. Java's NIO uses the approach implemented here and appears to ignore
+//    `FILE_ID_INFO` altogether. So Java's NIO and this code are
+//    susceptible to bugs when running on a file system where
+//    `nFileIndex{Low,High}` are not unique.
+//
+// 2. LLVM has a bug where they fetch the id of a file and continue to use
+//    it even after the handle has been closed, so that uniqueness is no
+//    longer guaranteed (when `nFileIndex{Low,High}` are unique).
+//    bug report: http://lists.llvm.org/pipermail/llvm-bugs/2014-December/037218.html
+//
+// All said and done, checking whether two files are the same on Windows
+// seems quite tricky. Moreover, even if the code is technically incorrect,
+// it seems like the chances of actually observing incorrect behavior are
+// extremely small. Nevertheless, we mitigate this by checking size too.
+//
+// In the case where this code is erroneous, two files will be reported
+// as equivalent when they are in fact distinct. This will cause the loop
+// detection code to report a false positive, which will prevent descending
+// into the offending directory. As far as failure modes goes, this isn't
+// that bad.
+
+#[derive(Debug)]
+pub struct Handle {
+    kind: HandleKind,
+    key: Option<Key>,
+}
+
+#[derive(Debug)]
+enum HandleKind {
+    /// Used when opening a file or acquiring ownership of a file.
+    Owned(winutil::Handle),
+    /// Used for stdio.
+    Borrowed(winutil::HandleRef),
+}
+
+#[derive(Debug, Eq, PartialEq, Hash)]
+struct Key {
+    volume: u64,
+    index: u64,
+}
+
+impl Eq for Handle {}
+
+impl PartialEq for Handle {
+    fn eq(&self, other: &Handle) -> bool {
+        // Need this branch to satisfy `Eq` since `Handle`s with
+        // `key.is_none()` wouldn't otherwise.
+        if self as *const Handle == other as *const Handle {
+            return true;
+        } else if self.key.is_none() || other.key.is_none() {
+            return false;
+        }
+        self.key == other.key
+    }
+}
+
+impl AsRawHandle for crate::Handle {
+    fn as_raw_handle(&self) -> RawHandle {
+        match self.0.kind {
+            HandleKind::Owned(ref h) => h.as_raw_handle(),
+            HandleKind::Borrowed(ref h) => h.as_raw_handle(),
+        }
+    }
+}
+
+impl IntoRawHandle for crate::Handle {
+    fn into_raw_handle(self) -> RawHandle {
+        match self.0.kind {
+            HandleKind::Owned(h) => h.into_raw_handle(),
+            HandleKind::Borrowed(h) => h.as_raw_handle(),
+        }
+    }
+}
+
+impl Hash for Handle {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.key.hash(state);
+    }
+}
+
+impl Handle {
+    pub fn from_path<P: AsRef<Path>>(p: P) -> io::Result<Handle> {
+        let h = winutil::Handle::from_path_any(p)?;
+        let info = winutil::file::information(&h)?;
+        Ok(Handle::from_info(HandleKind::Owned(h), info))
+    }
+
+    pub fn from_file(file: File) -> io::Result<Handle> {
+        let h = winutil::Handle::from_file(file);
+        let info = winutil::file::information(&h)?;
+        Ok(Handle::from_info(HandleKind::Owned(h), info))
+    }
+
+    fn from_std_handle(h: winutil::HandleRef) -> io::Result<Handle> {
+        match winutil::file::information(&h) {
+            Ok(info) => Ok(Handle::from_info(HandleKind::Borrowed(h), info)),
+            // In a Windows console, if there is no pipe attached to a STD
+            // handle, then GetFileInformationByHandle will return an error.
+            // We don't really care. The only thing we care about is that
+            // this handle is never equivalent to any other handle, which is
+            // accomplished by setting key to None.
+            Err(_) => Ok(Handle { kind: HandleKind::Borrowed(h), key: None }),
+        }
+    }
+
+    fn from_info(
+        kind: HandleKind,
+        info: winutil::file::Information,
+    ) -> Handle {
+        Handle {
+            kind: kind,
+            key: Some(Key {
+                volume: info.volume_serial_number(),
+                index: info.file_index(),
+            }),
+        }
+    }
+
+    pub fn stdin() -> io::Result<Handle> {
+        Handle::from_std_handle(winutil::HandleRef::stdin())
+    }
+
+    pub fn stdout() -> io::Result<Handle> {
+        Handle::from_std_handle(winutil::HandleRef::stdout())
+    }
+
+    pub fn stderr() -> io::Result<Handle> {
+        Handle::from_std_handle(winutil::HandleRef::stderr())
+    }
+
+    pub fn as_file(&self) -> &File {
+        match self.kind {
+            HandleKind::Owned(ref h) => h.as_file(),
+            HandleKind::Borrowed(ref h) => h.as_file(),
+        }
+    }
+
+    pub fn as_file_mut(&mut self) -> &mut File {
+        match self.kind {
+            HandleKind::Owned(ref mut h) => h.as_file_mut(),
+            HandleKind::Borrowed(ref mut h) => h.as_file_mut(),
+        }
+    }
+}