Implement AsFile for dyn Handle

This cleans up a lot of repeating boilerplate code todo with
dynamic dispatch.

Author: Jakub Konka

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

@@ -29,6 +29,7 @@ use crate::wasi::types;
 use osdir::OsDir;
 use osfile::OsFile;
 use osother::OsOther;
+use stdio::Stdio;
 use std::convert::TryFrom;
 use std::fs::File;
 use std::io;
@@ -39,6 +40,22 @@ pub(crate) trait AsFile {
     fn as_file(&self) -> ManuallyDrop<File>;
 }
 
+impl AsFile for dyn Handle + 'static {
+    fn as_file(&self) -> ManuallyDrop<File> {
+        if let Some(file) = self.as_any().downcast_ref::<OsFile>() {
+            file.as_file()
+        } else if let Some(dir) = self.as_any().downcast_ref::<OsDir>() {
+            dir.as_file()
+        } else if let Some(stdio) = self.as_any().downcast_ref::<Stdio>() {
+            stdio.as_file()
+        } else if let Some(other) = self.as_any().downcast_ref::<OsOther>() {
+            other.as_file()
+        } else {
+            panic!("non-OS resource cannot be made into a File")
+        }
+    }
+}
+
 impl TryFrom<File> for Box<dyn Handle> {
     type Error = io::Error;
 

crates/wasi-common/src/sys/osdir.rs

@@ -97,7 +97,7 @@ impl Handle for OsDir {
     ) -> Result<()> {
         let new_handle = match new_handle.as_any().downcast_ref::<Self>() {
             None => {
-                error!("Tried to link OS resource with Virtual");
+                error!("Tried to link with handle that's not an OsDir");
                 return Err(Errno::Badf);
             }
             Some(handle) => handle,
@@ -116,7 +116,7 @@ impl Handle for OsDir {
     fn rename(&self, old_path: &str, new_handle: Box<dyn Handle>, new_path: &str) -> Result<()> {
         let new_handle = match new_handle.as_any().downcast_ref::<Self>() {
             None => {
-                error!("Tried to link OS resource with Virtual");
+                error!("Tried to rename with handle that's not an OsDir");
                 return Err(Errno::Badf);
             }
             Some(handle) => handle,

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

@@ -5,14 +5,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::File;
 use std::io;
-use std::ops::Deref;
-use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
-
-impl AsRawFd for OsDir {
-    fn as_raw_fd(&self) -> RawFd {
-        self.deref().as_raw_fd()
-    }
-}
+use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd};
 
 impl TryFrom<File> for OsDir {
     type Error = io::Error;

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

@@ -5,14 +5,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::{File, OpenOptions};
 use std::io;
-use std::ops::Deref;
-use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
-
-impl AsRawFd for OsFile {
-    fn as_raw_fd(&self) -> RawFd {
-        self.deref().as_raw_fd()
-    }
-}
+use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd};
 
 impl TryFrom<File> for OsFile {
     type Error = io::Error;

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

@@ -6,14 +6,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::File;
 use std::io;
-use std::ops::Deref;
-use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
-
-impl AsRawFd for OsOther {
-    fn as_raw_fd(&self) -> RawFd {
-        self.deref().as_raw_fd()
-    }
-}
+use std::os::unix::prelude::{AsRawFd, FromRawFd, IntoRawFd};
 
 impl TryFrom<File> for OsOther {
     type Error = io::Error;

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

@@ -1,9 +1,6 @@
 use crate::entry::EntryHandle;
 use crate::poll::{ClockEventData, FdEventData};
-use crate::sys::osdir::OsDir;
 use crate::sys::osfile::OsFile;
-use crate::sys::osother::OsOther;
-use crate::sys::stdio::Stdio;
 use crate::sys::AsFile;
 use crate::wasi::{types, Errno, Result};
 use std::io;
@@ -32,18 +29,7 @@ pub(crate) fn oneoff(
                 // events we filtered before. If we get something else here, the code has a serious bug.
                 _ => unreachable!(),
             };
-            let fd = if let Some(file) = event.handle.as_any().downcast_ref::<OsFile>() {
-                file.as_raw_fd()
-            } else if let Some(dir) = event.handle.as_any().downcast_ref::<OsDir>() {
-                dir.as_raw_fd()
-            } else if let Some(stdio) = event.handle.as_any().downcast_ref::<Stdio>() {
-                stdio.as_raw_fd()
-            } else if let Some(other) = event.handle.as_any().downcast_ref::<OsOther>() {
-                other.as_raw_fd()
-            } else {
-                panic!("can poll FdEvent for OS resources only")
-            };
-            unsafe { PollFd::new(fd, flags) }
+            unsafe { PollFd::new(event.handle.as_file().as_raw_fd(), flags) }
         })
         .collect();
 
@@ -97,16 +83,9 @@ fn handle_fd_event(
             let meta = file.as_file().metadata()?;
             let len = meta.len();
             let host_offset = unsafe { tell(file.as_raw_fd())? };
-            Ok(len - host_offset)
-        } else if let Some(dir) = handle.as_any().downcast_ref::<OsDir>() {
-            unsafe { Ok(fionread(dir.as_raw_fd())?.into()) }
-        } else if let Some(stdio) = handle.as_any().downcast_ref::<Stdio>() {
-            unsafe { Ok(fionread(stdio.as_raw_fd())?.into()) }
-        } else if let Some(other) = handle.as_any().downcast_ref::<OsOther>() {
-            unsafe { Ok(fionread(other.as_raw_fd())?.into()) }
-        } else {
-            panic!("can poll FdEvent for OS resources only")
+            return Ok(len - host_offset);
         }
+        Ok(unsafe { fionread(handle.as_file().as_raw_fd())?.into() })
     }
 
     for (fd_event, poll_fd) in ready_events {

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

@@ -5,14 +5,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::File;
 use std::io;
-use std::ops::Deref;
-use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
-
-impl AsRawHandle for OsDir {
-    fn as_raw_handle(&self) -> RawHandle {
-        self.deref().as_raw_handle()
-    }
-}
+use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle};
 
 impl TryFrom<File> for OsDir {
     type Error = io::Error;

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

@@ -5,14 +5,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::{File, OpenOptions};
 use std::io;
-use std::ops::Deref;
-use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
-
-impl AsRawHandle for OsFile {
-    fn as_raw_handle(&self) -> RawHandle {
-        self.deref().as_raw_handle()
-    }
-}
+use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle};
 
 impl TryFrom<File> for OsFile {
     type Error = io::Error;

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

@@ -6,14 +6,7 @@ use crate::wasi::{types, RightsExt};
 use std::convert::TryFrom;
 use std::fs::File;
 use std::io;
-use std::ops::Deref;
-use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
-
-impl AsRawHandle for OsOther {
-    fn as_raw_handle(&self) -> RawHandle {
-        self.deref().as_raw_handle()
-    }
-}
+use std::os::windows::prelude::{FromRawHandle, IntoRawHandle};
 
 impl TryFrom<File> for OsOther {
     type Error = io::Error;

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

@@ -145,42 +145,16 @@ fn handle_timeout_event(timeout_event: ClockEventData, events: &mut Vec<types::E
 
 fn handle_rw_event(event: FdEventData, out_events: &mut Vec<types::Event>) {
     let handle = &event.handle;
-    let size = if let Some(file) = handle.as_any().downcast_ref::<OsFile>() {
-        if event.r#type == types::Eventtype::FdRead {
-            file.as_file()
-                .metadata()
-                .map(|m| m.len())
-                .map_err(Into::into)
-        } else {
-            // The spec is unclear what nbytes should actually be for __WASI_EVENTTYPE_FD_WRITE and
-            // the implementation on Unix just returns 0 here, so it's probably fine
-            // to do the same on Windows for now.
-            // cf. https://github.com/WebAssembly/WASI/issues/148
-            Ok(0)
-        }
-    } else if let Some(dir) = handle.as_any().downcast_ref::<OsDir>() {
-        if event.r#type == types::Eventtype::FdRead {
-            dir.as_file()
-                .metadata()
-                .map(|m| m.len())
-                .map_err(Into::into)
-        } else {
-            // The spec is unclear what nbytes should actually be for __WASI_EVENTTYPE_FD_WRITE and
-            // the implementation on Unix just returns 0 here, so it's probably fine
-            // to do the same on Windows for now.
-            // cf. https://github.com/WebAssembly/WASI/issues/148
-            Ok(0)
-        }
-    } else if let Some(stdio) = handle.as_any().downcast_ref::<Stdio>() {
+    let size = if let Some(stdio) = handle.as_any().downcast_ref::<Stdio>() {
         match stdio {
             // We return the only universally correct lower bound, see the comment later in the function.
             Stdio::In { .. } => Ok(1),
             // On Unix, ioctl(FIONREAD) will return 0 for stdout/stderr. Emulate the same behavior on Windows.
             Stdio::Out { .. } | Stdio::Err { .. } => Ok(0),
         }
-    } else if let Some(other) = handle.as_any().downcast_ref::<OsOther>() {
+    } else {
         if event.r#type == types::Eventtype::FdRead {
-            other
+            handle
                 .as_file()
                 .metadata()
                 .map(|m| m.len())
@@ -192,10 +166,7 @@ fn handle_rw_event(event: FdEventData, out_events: &mut Vec<types::Event>) {
             // cf. https://github.com/WebAssembly/WASI/issues/148
             Ok(0)
         }
-    } else {
-        panic!("can poll FdEvent for OS resources only")
     };
-
     let new_event = make_rw_event(&event, size);
     out_events.push(new_event);
 }