Support fd_fdstat_get and fd_renumber on stdin/stdout/stderr (#631)

* Support fd_fdstat_get on stdin/stdout/stderr.

Add a routine for obtaining an `OsFile` containing a file descriptor for
stdin/stdout/stderr so that we can do fd_fdstat_get on them.

* Add a testcase for fd_fdstat_get etc. on stdin etc.

* Don't dup file descriptors in fd_renumber.

* Fix compilation on macOS

* Rename OsFile to OsHandle

This commits renames `OsFile` to `OsHandle` which seems to make
more sense semantically as it is permitted to hold a valid OS handle
to OS entities other than simply file/dir (e.g., socket, stream, etc.).
As such, this commit also renames methods on `Descriptor` struct
from `as_actual_file` to `as_file` as this in reality does pertain
ops on FS entities such as files/dirs, and `as_file` to `as_os_handle`
as in this case it can be anything, from file, through a socket, to
a stream.

* Fix compilation on Linux

* Introduce `OsHandleRef` for borrowing OS resources.

To prevent a `ManuallyDrop<OsHandleRef>` from outliving the resource it
holds on to, create an `OsHandleRef` class parameterized on the lifetime
of the `Descriptor`.

* Fix scoping to pub-priv and backport to snapshot_0

crates/wasi-common/src/sys/unix/bsd/hostcalls_impl.rs

@@ -1,5 +1,5 @@
 use super::super::dir::{Dir, Entry, SeekLoc};
-use super::osfile::OsFile;
+use super::oshandle::OsHandle;
 use crate::hostcalls_impl::{Dirent, PathGet};
 use crate::sys::host_impl;
 use crate::sys::unix::str_to_cstring;
@@ -205,12 +205,12 @@ pub(crate) fn fd_advise(
 }
 
 pub(crate) fn fd_readdir<'a>(
-    os_file: &'a mut OsFile,
+    os_handle: &'a mut OsHandle,
     cookie: wasi::__wasi_dircookie_t,
 ) -> Result<impl Iterator<Item = Result<Dirent>> + 'a> {
     use std::sync::Mutex;
 
-    let dir = match os_file.dir {
+    let dir = match os_handle.dir {
         Some(ref mut dir) => dir,
         None => {
             // We need to duplicate the fd, because `opendir(3)`:
@@ -219,9 +219,9 @@ pub(crate) fn fd_readdir<'a>(
             //     descriptor, or to modify the state of the associated description other
             //     than by means of closedir(), readdir(), readdir_r(), or rewinddir(),
             //     the behaviour is undefined.
-            let fd = (*os_file).try_clone()?;
+            let fd = (*os_handle).try_clone()?;
             let dir = Dir::from(fd)?;
-            os_file.dir.get_or_insert(Mutex::new(dir))
+            os_handle.dir.get_or_insert(Mutex::new(dir))
         }
     };
     let mut dir = dir.lock().unwrap();

crates/wasi-common/src/sys/unix/bsd/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::{sys::host_impl, Result};

crates/wasi-common/src/sys/unix/bsd/oshandle.rs

@@ -5,9 +5,9 @@ use std::os::unix::prelude::{AsRawFd, RawFd};
 use std::sync::Mutex;
 
 #[derive(Debug)]
-pub(crate) struct OsFile {
+pub(crate) struct OsHandle {
     pub(crate) file: fs::File,
-    // In case that this `OsFile` actually refers to a directory,
+    // In case that this `OsHandle` actually refers to a directory,
     // when the client makes a `fd_readdir` syscall on this descriptor,
     // we will need to cache the `libc::DIR` pointer manually in order
     // to be able to seek on it later. While on Linux, this is handled
@@ -21,19 +21,19 @@ pub(crate) struct OsFile {
     pub(crate) dir: Option<Mutex<Dir>>,
 }
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self { file, dir: None }
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.file.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -41,7 +41,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.file
     }

crates/wasi-common/src/sys/unix/fdentry_impl.rs

@@ -1,11 +1,13 @@
-use crate::fdentry::Descriptor;
+use crate::fdentry::{Descriptor, OsHandleRef};
 use crate::{wasi, Error, Result};
+use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::os::unix::prelude::{AsRawFd, FileTypeExt, FromRawFd, RawFd};
 
 cfg_if::cfg_if! {
     if #[cfg(target_os = "linux")] {
-        pub(crate) use super::linux::osfile::*;
+        pub(crate) use super::linux::oshandle::*;
         pub(crate) use super::linux::fdentry_impl::*;
     } else if #[cfg(any(
             target_os = "macos",
@@ -15,7 +17,7 @@ cfg_if::cfg_if! {
             target_os = "ios",
             target_os = "dragonfly"
     ))] {
-        pub(crate) use super::bsd::osfile::*;
+        pub(crate) use super::bsd::oshandle::*;
         pub(crate) use super::bsd::fdentry_impl::*;
     }
 }
@@ -23,7 +25,7 @@ cfg_if::cfg_if! {
 impl AsRawFd for Descriptor {
     fn as_raw_fd(&self) -> RawFd {
         match self {
-            Self::OsFile(file) => file.as_raw_fd(),
+            Self::OsHandle(file) => file.as_raw_fd(),
             Self::Stdin => io::stdin().as_raw_fd(),
             Self::Stdout => io::stdout().as_raw_fd(),
             Self::Stderr => io::stderr().as_raw_fd(),
@@ -31,6 +33,14 @@ impl AsRawFd for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_fd(desc.as_raw_fd())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file descriptor.
 pub(crate) unsafe fn determine_type_and_access_rights<Fd: AsRawFd>(
     fd: &Fd,

crates/wasi-common/src/sys/unix/linux/mod.rs

@@ -1,6 +1,6 @@
 pub(crate) mod filetime;
 pub(crate) mod hostcalls_impl;
-pub(crate) mod osfile;
+pub(crate) mod oshandle;
 
 pub(crate) mod fdentry_impl {
     use crate::{sys::host_impl, Result};

crates/wasi-common/src/sys/unix/linux/oshandle.rs

@@ -3,21 +3,21 @@ use std::ops::{Deref, DerefMut};
 use std::os::unix::prelude::{AsRawFd, RawFd};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(fs::File);
+pub(crate) struct OsHandle(fs::File);
 
-impl From<fs::File> for OsFile {
+impl From<fs::File> for OsHandle {
     fn from(file: fs::File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawFd for OsFile {
+impl AsRawFd for OsHandle {
     fn as_raw_fd(&self) -> RawFd {
         self.0.as_raw_fd()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = fs::File;
 
     fn deref(&self) -> &Self::Target {
@@ -25,7 +25,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }

crates/wasi-common/src/sys/windows/fdentry_impl.rs

@@ -1,26 +1,27 @@
-use crate::fdentry::Descriptor;
+use crate::fdentry::{Descriptor, OsHandleRef};
 use crate::{wasi, Error, Result};
 use std::fs::File;
 use std::io;
+use std::mem::ManuallyDrop;
 use std::ops::{Deref, DerefMut};
 use std::os::windows::prelude::{AsRawHandle, FromRawHandle, RawHandle};
 
 #[derive(Debug)]
-pub(crate) struct OsFile(File);
+pub(crate) struct OsHandle(File);
 
-impl From<File> for OsFile {
+impl From<File> for OsHandle {
     fn from(file: File) -> Self {
         Self(file)
     }
 }
 
-impl AsRawHandle for OsFile {
+impl AsRawHandle for OsHandle {
     fn as_raw_handle(&self) -> RawHandle {
         self.0.as_raw_handle()
     }
 }
 
-impl Deref for OsFile {
+impl Deref for OsHandle {
     type Target = File;
 
     fn deref(&self) -> &Self::Target {
@@ -28,7 +29,7 @@ impl Deref for OsFile {
     }
 }
 
-impl DerefMut for OsFile {
+impl DerefMut for OsHandle {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.0
     }
@@ -37,7 +38,7 @@ impl DerefMut for OsFile {
 impl AsRawHandle for Descriptor {
     fn as_raw_handle(&self) -> RawHandle {
         match self {
-            Self::OsFile(file) => file.as_raw_handle(),
+            Self::OsHandle(file) => file.as_raw_handle(),
             Self::Stdin => io::stdin().as_raw_handle(),
             Self::Stdout => io::stdout().as_raw_handle(),
             Self::Stderr => io::stderr().as_raw_handle(),
@@ -45,6 +46,14 @@ impl AsRawHandle for Descriptor {
     }
 }
 
+pub(crate) fn descriptor_as_oshandle<'lifetime>(
+    desc: &'lifetime Descriptor,
+) -> OsHandleRef<'lifetime> {
+    OsHandleRef::new(ManuallyDrop::new(OsHandle::from(unsafe {
+        File::from_raw_handle(desc.as_raw_handle())
+    })))
+}
+
 /// This function is unsafe because it operates on a raw file handle.
 pub(crate) unsafe fn determine_type_and_access_rights<Handle: AsRawHandle>(
     handle: &Handle,

crates/wasi-common/src/sys/windows/hostcalls_impl/fs.rs

@@ -5,7 +5,7 @@ use crate::ctx::WasiCtx;
 use crate::fdentry::FdEntry;
 use crate::helpers::systemtime_to_timestamp;
 use crate::hostcalls_impl::{fd_filestat_set_times_impl, Dirent, FileType, PathGet};
-use crate::sys::fdentry_impl::{determine_type_rights, OsFile};
+use crate::sys::fdentry_impl::determine_type_rights;
 use crate::sys::host_impl::{self, path_from_host};
 use crate::sys::hostcalls_impl::fs_helpers::PathGetExt;
 use crate::{wasi, Error, Result};