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use std::alloc::Layout;
#[derive(Clone, Copy)]
#[repr(C)]
struct GSSmall {
len: u32,
data: [u8; 12],
}
#[derive(Clone, Copy)]
#[repr(C)]
struct GSLarge {
len: u32,
prefix: [u8; 4],
data: *mut u8,
}
const _ASSERT_VARIANTS_SIZE: () = assert!(
std::mem::size_of::<GSSmall>() == std::mem::size_of::<GSLarge>(),
"German String variants must have the same size"
);
union GSRepr {
small: GSSmall,
large: GSLarge,
}
#[repr(transparent)]
pub struct GermanString(GSRepr);
const _ASSERT_GSTRING_SIZE: () = assert!(
std::mem::size_of::<GermanString>() == 16,
"German String should be 16 bytes in size",
);
impl GermanString {
// Creates a new transient German String from the given bytes. Transient
// strings are destroyed when the object is destroyed. Persistent strings
// are not supported yet.
pub fn new_transient(bytes: &[u8]) -> GermanString {
if bytes.len() <= 12 {
let mut s = GSSmall {
len: bytes.len() as u32,
data: [0u8; 12],
};
s.data[..bytes.len()].copy_from_slice(bytes);
GermanString(GSRepr { small: s })
} else {
let layout = Layout::array::<u8>(bytes.len()).unwrap();
let mut large = GSLarge {
len: bytes.len() as u32,
prefix: [0u8; 4],
data: unsafe {
let ptr = std::alloc::alloc(layout);
if ptr.is_null() {
std::alloc::handle_alloc_error(layout);
}
std::ptr::copy_nonoverlapping(bytes.as_ptr(), ptr, bytes.len());
ptr
},
};
large.prefix.copy_from_slice(&bytes[..4]);
GermanString(GSRepr { large })
}
}
pub fn len(&self) -> usize {
// SAFETY: The length field is located in the same location for both
// variants, reading it from either is safe.
unsafe { self.0.small.len as usize }
}
pub fn as_bytes(&self) -> &[u8] {
if self.len() > 12 {
unsafe { std::slice::from_raw_parts(self.0.large.data, self.len()) }
} else {
unsafe { &self.0.small.data.as_ref()[..self.len()] }
}
}
pub fn as_str(&self) -> Result<&str, std::str::Utf8Error> {
std::str::from_utf8(self.as_bytes())
}
}
impl Drop for GermanString {
fn drop(&mut self) {
if self.len() > 12 {
let layout = Layout::array::<u8>(self.len()).unwrap();
unsafe {
std::alloc::dealloc(self.0.large.data, layout);
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_empty_string() {
let empty = GermanString::new_transient(b"");
assert_eq!(empty.len(), 0, "empty string should be empty");
assert_eq!(empty.as_bytes(), b"", "empty string should contain nothing");
assert_eq!(
empty.as_str().expect("empty string is valid UTF-8"),
"",
"empty string should contain empty string"
);
}
#[test]
fn test_short_string() {
let short = GermanString::new_transient(b"meow");
assert_eq!(short.len(), 4, "'meow' is four characters");
assert_eq!(
short.as_bytes(),
b"meow",
"short string returns correct bytes"
);
assert_eq!(
short.as_str().expect("'meow' is valid UTF-8"),
"meow",
"short string returns correct string"
);
}
#[test]
fn test_long_string() {
let input: &str = "This code was written at https://signal.live";
let long = GermanString::new_transient(input.as_bytes());
assert_eq!(long.len(), 44, "long string has correct length");
assert_eq!(
long.as_bytes(),
input.as_bytes(),
"long string returns correct bytes"
);
assert_eq!(
long.as_str().expect("input is valid UTF-8"),
input,
"long string returns correct string"
);
}
}
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