Add precise registry types and allocation-free queries and updates (#…

…3184)

crates/libs/registry/src/data.rs

@@ -0,0 +1,129 @@
+use super::*;
+
+// Minimal `Vec<u8>` replacement providing at least `u16` alignment so that it can be used for wide strings.
+pub struct Data {
+    ptr: *mut u8,
+    len: usize,
+}
+
+impl Data {
+    // Creates a buffer with the specified length of zero bytes.
+    pub fn new(len: usize) -> Result<Self> {
+        unsafe {
+            let bytes = Self::alloc(len)?;
+
+            if len > 0 {
+                core::ptr::write_bytes(bytes.ptr, 0, len);
+            }
+
+            Ok(bytes)
+        }
+    }
+
+    // Returns the buffer as a slice of u16 for reading wide characters. The slice trims off any trailing zero bytes.
+    pub fn as_wide(&self) -> &[u16] {
+        if self.ptr.is_null() {
+            &[]
+        } else {
+            let mut wide =
+                unsafe { core::slice::from_raw_parts(self.ptr as *const u16, self.len / 2) };
+
+            while wide.last() == Some(&0) {
+                wide = &wide[..wide.len() - 1];
+            }
+
+            wide
+        }
+    }
+
+    // Creates a buffer by copying the bytes from the slice.
+    pub fn from_slice(slice: &[u8]) -> Result<Self> {
+        unsafe {
+            let bytes = Self::alloc(slice.len())?;
+
+            if !slice.is_empty() {
+                core::ptr::copy_nonoverlapping(slice.as_ptr(), bytes.ptr, slice.len());
+            }
+
+            Ok(bytes)
+        }
+    }
+
+    // Allocates an uninitialized buffer.
+    unsafe fn alloc(len: usize) -> Result<Self> {
+        if len == 0 {
+            Ok(Self {
+                ptr: null_mut(),
+                len: 0,
+            })
+        } else {
+            // This pointer will have at least 8 byte alignment.
+            let ptr = HeapAlloc(GetProcessHeap(), 0, len) as *mut u8;
+
+            if ptr.is_null() {
+                Err(Error::from_hresult(HRESULT::from_win32(ERROR_OUTOFMEMORY)))
+            } else {
+                Ok(Self { ptr, len })
+            }
+        }
+    }
+}
+
+impl Drop for Data {
+    fn drop(&mut self) {
+        if !self.ptr.is_null() {
+            unsafe {
+                HeapFree(GetProcessHeap(), 0, self.ptr as *mut _);
+            }
+        }
+    }
+}
+
+impl Deref for Data {
+    type Target = [u8];
+
+    fn deref(&self) -> &[u8] {
+        if self.ptr.is_null() {
+            &[]
+        } else {
+            unsafe { core::slice::from_raw_parts(self.ptr, self.len) }
+        }
+    }
+}
+
+impl core::ops::DerefMut for Data {
+    fn deref_mut(&mut self) -> &mut [u8] {
+        if self.ptr.is_null() {
+            &mut []
+        } else {
+            unsafe { core::slice::from_raw_parts_mut(self.ptr, self.len) }
+        }
+    }
+}
+
+impl Clone for Data {
+    fn clone(&self) -> Self {
+        Self::from_slice(self).unwrap()
+    }
+}
+
+impl PartialEq for Data {
+    fn eq(&self, other: &Self) -> bool {
+        self.deref() == other.deref()
+    }
+}
+
+impl Eq for Data {}
+
+impl core::fmt::Debug for Data {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        self.deref().fmt(f)
+    }
+}
+
+impl<const N: usize> TryFrom<[u8; N]> for Data {
+    type Error = Error;
+    fn try_from(from: [u8; N]) -> Result<Self> {
+        Self::from_slice(&from)
+    }
+}