Add HSTRING builder and registry support

crates/libs/registry/Cargo.toml

@@ -24,3 +24,7 @@ path = "../targets"
 [dependencies.windows-result]
 version = "0.1.1"
 path = "../result"
+
+[dependencies.windows-strings]
+version = "0.1.0"
+path = "../strings"

crates/libs/registry/src/key.rs

@@ -98,6 +98,15 @@ impl Key {
         unsafe { self.set_value(name, REG_SZ, value.as_ptr() as _, value.len() * 2) }
     }
 
+    /// Sets the name and value in the registry key.
+    pub fn set_hstring<T: AsRef<str>>(
+        &self,
+        name: T,
+        value: &windows_strings::HSTRING,
+    ) -> Result<()> {
+        unsafe { self.set_value(name, REG_SZ, value.as_ptr() as _, value.len() * 2) }
+    }
+
     /// Sets the name and value in the registry key.
     pub fn set_multi_string<T: AsRef<str>>(&self, name: T, value: &[T]) -> Result<()> {
         let mut packed = value.iter().fold(vec![0u16; 0], |mut packed, value| {
@@ -278,6 +287,40 @@ impl Key {
         }
     }
 
+    /// Gets the value for the name in the registry key.
+    pub fn get_hstring<T: AsRef<str>>(&self, name: T) -> Result<HSTRING> {
+        let name = pcwstr(name);
+        let mut ty = 0;
+        let mut len = 0;
+
+        let result = unsafe {
+            RegQueryValueExW(self.0, name.as_ptr(), null(), &mut ty, null_mut(), &mut len)
+        };
+
+        win32_error(result)?;
+
+        if !matches!(ty, REG_SZ | REG_EXPAND_SZ) {
+            return Err(invalid_data());
+        }
+
+        let mut value = HStringBuilder::new(len as usize / 2)?;
+
+        let result = unsafe {
+            RegQueryValueExW(
+                self.0,
+                name.as_ptr(),
+                null(),
+                null_mut(),
+                value.as_mut_ptr() as _,
+                &mut len,
+            )
+        };
+
+        win32_error(result)?;
+        value.trim_end();
+        Ok(value.into())
+    }
+
     /// Gets the value for the name in the registry key.
     pub fn get_bytes<T: AsRef<str>>(&self, name: T) -> Result<Vec<u8>> {
         let name = pcwstr(name);

crates/libs/registry/src/lib.rs

@@ -30,6 +30,9 @@ pub use r#type::Type;
 pub use windows_result::Result;
 use windows_result::*;
 
+pub use windows_strings::HSTRING;
+use windows_strings::*;
+
 /// The predefined `HKEY_CLASSES_ROOT` registry key.
 pub const CLASSES_ROOT: &Key = &Key(HKEY_CLASSES_ROOT);
 

crates/libs/result/src/bindings.rs

@@ -19,7 +19,6 @@ pub type BOOL = i32;
 pub type BSTR = *const u16;
 pub const ERROR_INVALID_DATA: WIN32_ERROR = 13u32;
 pub const ERROR_NO_UNICODE_TRANSLATION: WIN32_ERROR = 1113u32;
-pub const E_INVALIDARG: HRESULT = 0x80070057_u32 as _;
 pub const E_UNEXPECTED: HRESULT = 0x8000FFFF_u32 as _;
 pub const FORMAT_MESSAGE_ALLOCATE_BUFFER: FORMAT_MESSAGE_OPTIONS = 256u32;
 pub const FORMAT_MESSAGE_FROM_HMODULE: FORMAT_MESSAGE_OPTIONS = 2048u32;

crates/libs/strings/.natvis

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
   <Type Name="windows_strings::hstring::HSTRING">
-    <Intrinsic Name="header" Expression="(windows_strings::hstring::Header *)__0.tag" />
-    <Intrinsic Name="is_empty" Expression="__0.tag == 0" />
+    <Intrinsic Name="header" Expression="(windows_strings::hstring_header::HStringHeader *)__0" />
+    <Intrinsic Name="is_empty" Expression="__0 == 0" />
     <DisplayString Condition="is_empty()">""</DisplayString>
     <DisplayString>{header()->data,[header()->len]su}</DisplayString>
 

crates/libs/strings/src/hstring.rs

@@ -1,27 +1,27 @@
 use super::*;
 
-/// A WinRT string ([HSTRING](https://docs.microsoft.com/en-us/windows/win32/winrt/hstring))
-/// is reference-counted and immutable.
+/// An ([HSTRING](https://docs.microsoft.com/en-us/windows/win32/winrt/hstring))
+/// is a reference-counted and immutable UTF-16 string type.
 #[repr(transparent)]
-pub struct HSTRING(Option<core::ptr::NonNull<Header>>);
+pub struct HSTRING(pub(crate) *mut HStringHeader);
 
 impl HSTRING {
     /// Create an empty `HSTRING`.
     ///
     /// This function does not allocate memory.
     pub const fn new() -> Self {
-        Self(None)
+        Self(core::ptr::null_mut())
     }
 
     /// Returns `true` if the string is empty.
-    pub const fn is_empty(&self) -> bool {
+    pub fn is_empty(&self) -> bool {
         // An empty HSTRING is represented by a null pointer.
-        self.0.is_none()
+        self.0.is_null()
     }
 
     /// Returns the length of the string. The length is measured in `u16`s (UTF-16 code units), not including the terminating null character.
     pub fn len(&self) -> usize {
-        if let Some(header) = self.get_header() {
+        if let Some(header) = self.as_header() {
             header.len as usize
         } else {
             0
@@ -35,7 +35,7 @@ impl HSTRING {
 
     /// Returns a raw pointer to the `HSTRING` buffer.
     pub fn as_ptr(&self) -> *const u16 {
-        if let Some(header) = self.get_header() {
+        if let Some(header) = self.as_header() {
             header.data
         } else {
             const EMPTY: [u16; 1] = [0];
@@ -66,7 +66,7 @@ impl HSTRING {
             return Ok(Self::new());
         }
 
-        let ptr = Header::alloc(len.try_into()?)?;
+        let ptr = HStringHeader::alloc(len.try_into()?)?;
 
         // Place each utf-16 character into the buffer and
         // increase len as we go along.
@@ -79,11 +79,11 @@ impl HSTRING {
 
         // Write a 0 byte to the end of the buffer.
         (*ptr).data.offset((*ptr).len as isize).write(0);
-        Ok(Self(core::ptr::NonNull::new(ptr)))
+        Ok(Self(ptr))
     }
 
-    fn get_header(&self) -> Option<&Header> {
-        self.0.map(|header| unsafe { header.as_ref() })
+    fn as_header(&self) -> Option<&HStringHeader> {
+        unsafe { self.0.as_ref() }
     }
 }
 
@@ -95,8 +95,8 @@ impl Default for HSTRING {
 
 impl Clone for HSTRING {
     fn clone(&self) -> Self {
-        if let Some(header) = self.get_header() {
-            Self(core::ptr::NonNull::new(header.duplicate().unwrap()))
+        if let Some(header) = self.as_header() {
+            Self(header.duplicate().unwrap())
         } else {
             Self::new()
         }
@@ -105,17 +105,12 @@ impl Clone for HSTRING {
 
 impl Drop for HSTRING {
     fn drop(&mut self) {
-        if self.is_empty() {
-            return;
-        }
-
-        if let Some(header) = self.0.take() {
-            // REFERENCE_FLAG indicates a string backed by static or stack memory that is
+        if let Some(header) = self.as_header() {
+            // HSTRING_REFERENCE_FLAG indicates a string backed by static or stack memory that is
             // thus not reference-counted and does not need to be freed.
             unsafe {
-                let header = header.as_ref();
-                if header.flags & REFERENCE_FLAG == 0 && header.count.release() == 0 {
-                    heap_free(header as *const _ as *mut _);
+                if header.flags & HSTRING_REFERENCE_FLAG == 0 && header.count.release() == 0 {
+                    HStringHeader::free(self.0);
                 }
             }
         }
@@ -407,54 +402,3 @@ impl From<HSTRING> for std::ffi::OsString {
         Self::from(&hstring)
     }
 }
-
-const REFERENCE_FLAG: u32 = 1;
-
-#[repr(C)]
-struct Header {
-    flags: u32,
-    len: u32,
-    _0: u32,
-    _1: u32,
-    data: *mut u16,
-    count: RefCount,
-    buffer_start: u16,
-}
-
-impl Header {
-    fn alloc(len: u32) -> Result<*mut Header> {
-        debug_assert!(len != 0);
-        // Allocate enough space for header and two bytes per character.
-        // The space for the terminating null character is already accounted for inside of `Header`.
-        let alloc_size = core::mem::size_of::<Header>() + 2 * len as usize;
-
-        let header = heap_alloc(alloc_size)? as *mut Header;
-
-        unsafe {
-            // Use `ptr::write` (since `header` is unintialized). `Header` is safe to be all zeros.
-            header.write(core::mem::MaybeUninit::<Header>::zeroed().assume_init());
-            (*header).len = len;
-            (*header).count = RefCount::new(1);
-            (*header).data = &mut (*header).buffer_start;
-        }
-
-        Ok(header)
-    }
-
-    fn duplicate(&self) -> Result<*mut Header> {
-        if self.flags & REFERENCE_FLAG == 0 {
-            // If this is not a "fast pass" string then simply increment the reference count.
-            self.count.add_ref();
-            Ok(self as *const Header as *mut Header)
-        } else {
-            // Otherwise, allocate a new string and copy the value into the new string.
-            let copy = Header::alloc(self.len)?;
-            // SAFETY: since we are duplicating the string it is safe to copy all data from self to the initialized `copy`.
-            // We copy `len + 1` characters since `len` does not account for the terminating null character.
-            unsafe {
-                core::ptr::copy_nonoverlapping(self.data, (*copy).data, self.len as usize + 1);
-            }
-            Ok(copy)
-        }
-    }
-}

crates/libs/strings/src/hstring_builder.rs

@@ -0,0 +1,83 @@
+use super::*;
+
+/// An [HSTRING] builder that supports preallocating the `HSTRING` to avoid extra allocations and copies.
+///
+/// This is similar to the `WindowsPreallocateStringBuffer` function but implemented directly in Rust for efficiency.
+/// It is implemented as a separate type since [HSTRING] values are immutable.
+pub struct HStringBuilder(*mut HStringHeader);
+
+impl HStringBuilder {
+    /// Creates a preallocated `HSTRING` value.
+    pub fn new(len: usize) -> Result<Self> {
+        Ok(Self(HStringHeader::alloc(len.try_into()?)?))
+    }
+
+    /// Shortens the string by removing any trailing 0 characters.
+    pub fn trim_end(&mut self) {
+        if let Some(header) = self.as_header_mut() {
+            while header.len > 0
+                && unsafe { header.data.offset(header.len as isize - 1).read() == 0 }
+            {
+                header.len -= 1;
+            }
+
+            if header.len == 0 {
+                unsafe {
+                    HStringHeader::free(self.0);
+                }
+                self.0 = core::ptr::null_mut();
+            }
+        }
+    }
+
+    fn as_header(&self) -> Option<&HStringHeader> {
+        unsafe { self.0.as_ref() }
+    }
+
+    fn as_header_mut(&mut self) -> Option<&mut HStringHeader> {
+        unsafe { self.0.as_mut() }
+    }
+}
+
+impl From<HStringBuilder> for HSTRING {
+    fn from(value: HStringBuilder) -> Self {
+        if let Some(header) = value.as_header() {
+            unsafe { header.data.offset(header.len as isize).write(0) };
+            let result = Self(value.0);
+            core::mem::forget(value);
+            result
+        } else {
+            Self::new()
+        }
+    }
+}
+
+impl core::ops::Deref for HStringBuilder {
+    type Target = [u16];
+
+    fn deref(&self) -> &[u16] {
+        if let Some(header) = self.as_header() {
+            unsafe { core::slice::from_raw_parts(header.data, header.len as usize) }
+        } else {
+            &[]
+        }
+    }
+}
+
+impl core::ops::DerefMut for HStringBuilder {
+    fn deref_mut(&mut self) -> &mut [u16] {
+        if let Some(header) = self.as_header() {
+            unsafe { core::slice::from_raw_parts_mut(header.data, header.len as usize) }
+        } else {
+            &mut []
+        }
+    }
+}
+
+impl Drop for HStringBuilder {
+    fn drop(&mut self) {
+        unsafe {
+            HStringHeader::free(self.0);
+        }
+    }
+}