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use super::*;
pub const HSTRING_REFERENCE_FLAG: u32 = 1;
#[repr(C)]
pub struct HStringHeader {
pub flags: u32,
pub len: u32,
pub _0: u32,
pub _1: u32,
pub data: *mut u16,
pub count: RefCount,
pub buffer_start: u16,
}
impl HStringHeader {
pub fn alloc(len: u32) -> Result<*mut Self> {
if len == 0 {
return Ok(core::ptr::null_mut());
}
// Allocate enough space for header and two bytes per character.
// The space for the terminating null character is already accounted for inside of `HStringHeader`.
let bytes = core::mem::size_of::<Self>() + 2 * len as usize;
let header =
unsafe { bindings::HeapAlloc(bindings::GetProcessHeap(), 0, bytes) } as *mut Self;
if header.is_null() {
return Err(Error::from_hresult(HRESULT(bindings::E_OUTOFMEMORY)));
}
unsafe {
// Use `ptr::write` (since `header` is unintialized). `HStringHeader` is safe to be all zeros.
header.write(core::mem::MaybeUninit::<Self>::zeroed().assume_init());
(*header).len = len;
(*header).count = RefCount::new(1);
(*header).data = &mut (*header).buffer_start;
}
Ok(header)
}
pub unsafe fn free(header: *mut Self) {
if header.is_null() {
return;
}
bindings::HeapFree(bindings::GetProcessHeap(), 0, header as *mut _);
}
pub fn duplicate(&self) -> Result<*mut Self> {
if self.flags & HSTRING_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 Self as *mut Self)
} else {
// Otherwise, allocate a new string and copy the value into the new string.
let copy = Self::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)
}
}
}