## Summary of the Pull Request
The File Locksmith IPC layer reads and writes raw UTF-16 (WCHAR) bytes
to `last-run.log`, but all three stream opens were using the default
text mode. On Windows, the CRT translates `0x0A` bytes to `0x0D 0x0A` on
write and collapses `0x0D 0x0A` back to `0x0A` on read. Because each
WCHAR is 2 bytes, any code unit whose little-endian byte pair contains
`0x0A` in the low position (e.g. `U+010A`, `U+0A0D`) is silently
corrupted. The fix opens all three streams in binary mode and adds an
explicit open-failure guard.
```cpp
// IPC.cpp — Writer::start()
// Before
m_stream = std::ofstream(path);
// After
m_stream = std::ofstream(path, std::ios::binary);
// + is_open() guard returning E_FAIL on failure
// NativeMethods.cpp — StartAsElevated() writer
// Before
std::ofstream stream(paths_file());
// After
std::ofstream stream(paths_file(), std::ios::binary);
// NativeMethods.cpp — ReadPathsFromFile() reader
// Before
std::ifstream stream(paths_file());
// After
std::ifstream stream(paths_file(), std::ios::binary);
```
## PR Checklist
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx
## Detailed Description of the Pull Request / Additional comments
Three targeted changes across two files:
1. **`FileLocksmithLib/IPC.cpp` — `Writer::start()`**: switched
`std::ofstream` from text to binary mode and added an `is_open()` check
that returns `E_FAIL` immediately when the file cannot be opened
(previously the try/catch did not catch a silent open failure because
`std::ofstream` does not throw by default).
2. **`FileLocksmithLibInterop/NativeMethods.cpp` —
`StartAsElevated()`**: switched `std::ofstream` from text to binary
mode. This is the elevated-restart writer path; without this fix,
Unicode corruption persisted when File Locksmith relaunched as
administrator.
3. **`FileLocksmithLibInterop/NativeMethods.cpp` —
`ReadPathsFromFile()`**: switched `std::ifstream` from text to binary
mode. This is the symmetric reader-side bug — even with both writers
corrected, the CRT text-mode reader could collapse a `0x0D 0x0A` byte
pair (a valid UTF-16 LE code unit, e.g. U+0A0D GURMUKHI EK ONKAR) into a
single byte, desynchronising the 2-bytes-at-a-time read loop and
corrupting all subsequent path data.
No behaviour change for purely ASCII paths. Paths containing Unicode
code points whose little-endian UTF-16 byte pair spans `0x0D 0x0A` were
silently corrupted in all three code paths before this fix.
## Validation Steps Performed
- Code review: no issues flagged.
- Full diff reviewed: all three stream opens (`ofstream` writer in
`IPC.cpp`, `ofstream` writer in `NativeMethods.cpp`, `ifstream` reader
in `NativeMethods.cpp`) now use `std::ios::binary`, making write and
read paths byte-exact and symmetric.
- Mechanically correct: `std::ios::binary` suppresses Windows CRT
`\n`↔`\r\n` translation; the delimiter `L'\n'` (LE bytes `0x0A 0x00`) is
unambiguous in binary mode and is handled correctly by the existing read
loop.
---------
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: MuyuanMS <116717757+MuyuanMS@users.noreply.github.com>
Co-authored-by: Muyuan Li (from Dev Box) <muyuanli@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
