hg: add osstring_to_local_bytes function to the encoding crate

Summary: Another convenience method that I plan to use in the `hgmain` later.

Reviewed By: quark-zju

Differential Revision: D9441426

fbshipit-source-id: 007e4932a344b9d1c8d4d654152bcca5c2362431

lib/encoding/src/lib.rs

@@ -21,6 +21,7 @@ mod unix;
 pub use unix::{
     local_bytes_to_osstring,
     local_bytes_to_path,
+    osstring_to_local_bytes,
     path_to_local_bytes
 };
 
@@ -28,6 +29,7 @@ pub use unix::{
 pub use windows::{
     local_bytes_to_osstring,
     local_bytes_to_path,
+    osstring_to_local_bytes,
     path_to_local_bytes
 };
 

lib/encoding/src/unix.rs

@@ -26,3 +26,8 @@ pub fn path_to_local_bytes(path: &Path) -> io::Result<&[u8]> {
 pub fn local_bytes_to_path(bytes: &[u8]) -> io::Result<&Path> {
     Ok(Path::new(local_bytes_to_osstring(bytes)?))
 }
+
+#[inline]
+pub fn osstring_to_local_bytes<S: AsRef<OsStr>>(s: &S) -> io::Result<&[u8]> {
+    Ok(s.as_ref().as_bytes())
+}

lib/encoding/src/windows.rs

@@ -7,12 +7,13 @@ use std::io::ErrorKind::InvalidInput;
 use winapi;
 use kernel32;
 use local_encoding::{Encoder, Encoding};
-use std::os::windows::ffi::OsStringExt;
-use std::ffi::OsString;
+use std::os::windows::ffi::{OsStringExt, OsStrExt};
+use std::ffi::{OsString, OsStr};
 use std::path::{Path, PathBuf};
 use winapi;
 
 const MB_ERR_INVALID_CHARS: winapi::DWORD = 0x00000008;
+const WC_COMPOSITECHECK: winapi::DWORD = 0x00000200;
 
 /// Convert local bytes into an `OsString`
 /// Since this is a Windows-specific version of this function,
@@ -51,7 +52,7 @@ pub fn local_bytes_to_osstring(bytes: &[u8]) -> io::Result<OsString> {
             len,
         )
     };
-    if len > 0 {
+    if len as usize == wide.len() {
         Ok(OsString::from_wide(&wide))
     } else {
         Err(io::Error::last_os_error())
@@ -79,4 +80,48 @@ pub fn path_to_local_bytes(path: &Path) -> io::Result<Vec<u8>> {
 #[inline]
 pub fn local_bytes_to_path(bytes: &[u8]) -> io::Result<PathBuf> {
     Ok(PathBuf::from(local_bytes_to_osstring(bytes)?))
-}
+}
+
+#[inline]
+pub fn osstring_to_local_bytes<S: AsRef<OsStr>>(s: &S) -> io::Result<Vec<u8>> {
+    let codepage = winapi::CP_ACP;
+    let s: &OsStr = s.as_ref();
+    if s.len() == 0 {
+        return Ok(Vec::new());
+    }
+    let wstr: Vec<u16> = s.encode_wide().collect();
+    let len = unsafe {
+        kernel32::WideCharToMultiByte(
+            codepage,
+            WC_COMPOSITECHECK,
+            wstr.as_ptr(),
+            wstr.len() as i32,
+            std::ptr::null_mut(),
+            0,
+            std::ptr::null(),
+            std::ptr::null_mut(),
+        )
+    };
+    if len == 0 {
+        return Err(io::Error::last_os_error());
+    }
+    let mut astr: Vec<u8> = Vec::with_capacity(len as usize);
+    let len = unsafe {
+        astr.set_len(len as usize);
+        kernel32::WideCharToMultiByte(
+            codepage,
+            WC_COMPOSITECHECK,
+            wstr.as_ptr(),
+            wstr.len() as i32,
+            astr.as_mut_ptr() as winapi::LPSTR,
+            len,
+            std::ptr::null(),
+            std::ptr::null_mut(),
+        )
+    };
+    if len as usize == astr.len() {
+        Ok(astr)
+    } else {
+        Err(io::Error::last_os_error())
+    }
+}