Implement fd_filestat_get for all platforms (#42)

* Implement fd_filestat_get for all platforms

* Remove an old comment

* Remove panics from the syscall wrappers

* Return WASI error type

* Reuse Metadata if possible to save syscalls.

* Refactor the change for two separate fd_filestat_get_impl

* Refactor error handling

src/sys/windows/hostcalls_impl/fs.rs

@@ -3,11 +3,13 @@
 use super::fs_helpers::*;
 use crate::ctx::WasiCtx;
 use crate::fdentry::FdEntry;
-use crate::sys::errno_from_host;
+use crate::helpers::systemtime_to_timestamp;
+use crate::sys::{errno_from_ioerror, errno_from_host};
 use crate::sys::fdentry_impl::determine_type_rights;
 use crate::sys::host_impl;
 use crate::{host, Result};
-use std::fs::File;
+use std::convert::TryInto;
+use std::fs::{File, Metadata};
 use std::io::{self, Seek, SeekFrom};
 use std::os::windows::fs::FileExt;
 use std::os::windows::prelude::{AsRawHandle, FromRawHandle};
@@ -173,8 +175,65 @@ pub(crate) fn path_rename(
     unimplemented!("path_rename")
 }
 
-pub(crate) fn fd_filestat_get(fd: &File) -> Result<host::__wasi_filestat_t> {
-    unimplemented!("fd_filestat_get")
+pub(crate) fn num_hardlinks(file: &File, _metadata: &Metadata) -> io::Result<u64> {
+    Ok(winx::file::get_fileinfo(file)?.nNumberOfLinks.into())
+}
+
+pub(crate) fn device_id(file: &File, _metadata: &Metadata) -> io::Result<u64> {
+    Ok(winx::file::get_fileinfo(file)?.dwVolumeSerialNumber.into())
+}
+
+pub(crate) fn file_serial_no(file: &File, _metadata: &Metadata) -> io::Result<u64> {
+    let info = winx::file::get_fileinfo(file)?;
+    let high = info.nFileIndexHigh;
+    let low = info.nFileIndexLow;
+    let no = ((high as u64) << 32) | (low as u64);
+    Ok(no)
+}
+
+pub(crate) fn change_time(file: &File, _metadata: &Metadata) -> io::Result<i64> {
+    winx::file::change_time(file)
+}
+
+pub(crate) fn fd_filestat_get_impl(file: &std::fs::File) -> Result<host::__wasi_filestat_t> {
+    let metadata = file.metadata().map_err(errno_from_ioerror)?;
+    Ok(host::__wasi_filestat_t {
+        st_dev: device_id(file, &metadata).map_err(errno_from_ioerror)?,
+        st_ino: file_serial_no(file, &metadata).map_err(errno_from_ioerror)?,
+        st_nlink: num_hardlinks(file, &metadata)
+            .map_err(errno_from_ioerror)?
+            .try_into()
+            .map_err(|_| host::__WASI_EOVERFLOW)?, // u64 doesn't fit into u32
+        st_size: metadata.len(),
+        st_atim: metadata
+            .accessed()
+            .map_err(errno_from_ioerror)
+            .and_then(systemtime_to_timestamp)?,
+        st_ctim: change_time(file, &metadata)
+            .map_err(errno_from_ioerror)?
+            .try_into()
+            .map_err(|_| host::__WASI_EOVERFLOW)?, // i64 doesn't fit into u64
+        st_mtim: metadata
+            .modified()
+            .map_err(errno_from_ioerror)
+            .and_then(systemtime_to_timestamp)?,
+        st_filetype: filetype(&metadata).map_err(errno_from_ioerror)?,
+    })
+}
+
+fn filetype(metadata: &Metadata) -> io::Result<host::__wasi_filetype_t> {
+    let ftype = metadata.file_type();
+    let ret = if ftype.is_file() {
+        host::__WASI_FILETYPE_REGULAR_FILE
+    } else if ftype.is_dir() {
+        host::__WASI_FILETYPE_DIRECTORY
+    } else if ftype.is_symlink() {
+        host::__WASI_FILETYPE_SYMBOLIC_LINK
+    } else {
+        host::__WASI_FILETYPE_UNKNOWN
+    };
+
+    Ok(ret)
 }
 
 pub(crate) fn fd_filestat_set_times(