Sanitize file/directory symlinks in path_symlinks on Windows

crates/wasi-common/src/old/snapshot_0/sys/windows/hostcalls_impl/fs.rs

@@ -11,7 +11,7 @@ use crate::old::snapshot_0::sys::hostcalls_impl::fs_helpers::PathGetExt;
 use crate::old::snapshot_0::wasi::{self, WasiError, WasiResult};
 use log::{debug, trace};
 use std::convert::TryInto;
-use std::fs::{File, Metadata, OpenOptions};
+use std::fs::{self, File, Metadata, OpenOptions};
 use std::io::{self, Seek, SeekFrom};
 use std::os::windows::fs::{FileExt, OpenOptionsExt};
 use std::os::windows::prelude::{AsRawHandle, FromRawHandle};
@@ -467,8 +467,21 @@ pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> WasiResult<()>
     let old_path = concatenate(resolved.dirfd(), Path::new(old_path))?;
     let new_path = resolved.concatenate()?;
 
-    // try creating a file symlink
-    let err = match symlink_file(&old_path, &new_path) {
+    // Windows distinguishes between file and directory symlinks.
+    // If the source doesn't exist or is an exotic file type, we fall back
+    // to regular file symlinks.
+    let use_dir_symlink = fs::metadata(&new_path)
+        .as_ref()
+        .map(Metadata::is_dir)
+        .unwrap_or(false);
+
+    let res = if use_dir_symlink {
+        symlink_dir(&old_path, &new_path)
+    } else {
+        symlink_file(&old_path, &new_path)
+    };
+
+    let err = match res {
         Ok(()) => return Ok(()),
         Err(e) => e,
     };
@@ -486,8 +499,15 @@ pub(crate) fn path_symlink(old_path: &str, resolved: PathGet) -> WasiResult<()>
                         return Err(WasiError::EEXIST);
                     }
                 }
+                // If the target contains a trailing slash, the Windows API returns
+                // ERROR_INVALID_NAME (which corresponds to ENOENT) instead of
+                // ERROR_ALREADY_EXISTS (which corresponds to EEXIST)
+                //
+                // This concerns only trailing slashes (not backslashes) and
+                // only symbolic links (not hard links).
+                //
+                // Since POSIX will return EEXIST in such case, we simulate this behavior
                 winerror::ERROR_INVALID_NAME => {
-                    // does the target without trailing slashes exist?
                     if let Some(path) = strip_trailing_slashes_and_concatenate(&resolved)? {
                         if path.exists() {
                             return Err(WasiError::EEXIST);