use std::alloc::Layout;
use std::cmp::Ordering;
use std::fmt::{Debug, Formatter};
#[derive(Clone, Copy)]
#[repr(C)]
struct GSSmall {
len: u32,
data: [u8; 12],
}
#[derive(Clone, Copy)]
#[repr(transparent)]
struct StorageClassPtr(usize);
impl StorageClassPtr {
fn transient(ptr: *const u8) -> Self {
debug_assert!(
(ptr as usize & 0b1) == 0,
"pointer must be at least 2-byte aligned"
);
Self(ptr as usize)
}
fn persistent(ptr: *const u8) -> Self {
debug_assert!(
(ptr as usize & 0b1) == 0,
"pointer must be at least 2-byte aligned"
);
Self((ptr as usize) | 0b1)
}
fn as_ptr(&self) -> *const u8 {
(self.0 & !0b1) as *const u8
}
unsafe fn as_mut_ptr(&self) -> *mut u8 {
(self.0 & !0b1) as *mut u8
}
fn is_transient(&self) -> bool {
(self.0 & 0b1) == 0
}
}
#[derive(Clone, Copy)]
#[repr(C)]
struct GSLarge {
len: u32,
prefix: [u8; 4],
data: StorageClassPtr,
}
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 slice, copying the
/// data in the process.
pub fn transient(bytes: &[u8]) -> GermanString {
if bytes.len() > u32::MAX as usize {
panic!("GermanString maximum length is {} bytes", u32::MAX);
}
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());
StorageClassPtr::transient(ptr)
},
};
large.prefix.copy_from_slice(&bytes[..4]);
GermanString(GSRepr { large })
}
}
/// Creates a new transient German String from the given owned bytes. Short
/// strings will be copied into the string representation, long strings will
/// be moved out of the given vector without additional allocations.
pub fn transient_from_owned(bytes: Vec<u8>) -> GermanString {
if bytes.len() > u32::MAX as usize {
panic!("GermanString maximum length is {} bytes", u32::MAX);
}
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 md = std::mem::ManuallyDrop::new(bytes);
let mut large = GSLarge {
len: md.len() as u32,
prefix: [0u8; 4],
data: StorageClassPtr::transient(md.as_ptr()),
};
large.prefix.copy_from_slice(&md[..4]);
GermanString(GSRepr { large })
}
}
/// Creates a persistent German String from a static data buffer.
pub fn persistent(bytes: &'static [u8]) -> GermanString {
if bytes.len() > u32::MAX as usize {
panic!("GermanString maximum length is {} bytes", u32::MAX);
}
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 mut large = GSLarge {
len: bytes.len() as u32,
prefix: [0u8; 4],
data: StorageClassPtr::persistent(bytes.as_ptr()),
};
large.prefix.copy_from_slice(&bytes[..4]);
GermanString(GSRepr { large })
}
}
/// Creates a persistent German String by leaking the provided data.
pub fn persistent_leak(bytes: Vec<u8>) -> GermanString {
if bytes.len() > u32::MAX as usize {
panic!("GermanString maximum length is {} bytes", u32::MAX);
}
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 md = std::mem::ManuallyDrop::new(bytes);
let mut large = GSLarge {
len: md.len() as u32,
prefix: [0u8; 4],
data: StorageClassPtr::persistent(md.as_ptr()),
};
large.prefix.copy_from_slice(&md[..4]);
GermanString(GSRepr { large })
}
}
/// Creates a persistent German String from a static data buffer.
pub fn persistent_from_str(s: &'static str) -> GermanString {
GermanString::persistent(s.as_bytes())
}
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.as_ptr(), 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) {
unsafe {
if self.len() > 12 && self.0.large.data.is_transient() {
let layout = Layout::array::<u8>(self.len()).unwrap();
std::alloc::dealloc(self.0.large.data.as_mut_ptr(), layout);
}
}
}
}
impl PartialEq for GermanString {
fn eq(&self, other: &GermanString) -> bool {
if self.len() != other.len() {
return false;
}
unsafe {
if self.len() <= 12 {
return self.0.small.data[..self.len()] == other.0.small.data[..other.len()];
}
return self.0.large.data.as_ptr() == other.0.large.data.as_ptr()
|| (self.0.large.prefix == other.0.large.prefix
&& self.as_bytes() == other.as_bytes());
}
}
}
impl Eq for GermanString {}
impl Ord for GermanString {
fn cmp(&self, other: &GermanString) -> Ordering {
match (self.len().cmp(&12), other.len().cmp(&12)) {
// two small strings
(Ordering::Less | Ordering::Equal, Ordering::Less | Ordering::Equal) => unsafe {
self.0.small.data[..self.len()].cmp(&other.0.small.data[..other.len()])
},
// two large strings
(Ordering::Greater, Ordering::Greater) => unsafe {
match self.0.large.prefix.cmp(&other.0.large.prefix) {
Ordering::Equal => self.as_bytes().cmp(other.as_bytes()),
ordering => ordering,
}
},
// LHS large, RHS small
(Ordering::Greater, _) => {
let prefix_ordering =
unsafe { self.0.large.prefix.as_slice().cmp(&other.0.small.data[..4]) };
if prefix_ordering != Ordering::Equal {
return prefix_ordering;
}
self.as_bytes().cmp(other.as_bytes())
}
// LHS small, RHS large
(_, Ordering::Greater) => {
let prefix_ordering =
unsafe { self.0.small.data[..4].cmp(other.0.large.prefix.as_slice()) };
if prefix_ordering != Ordering::Equal {
return prefix_ordering;
}
self.as_bytes().cmp(other.as_bytes())
}
}
}
}
impl PartialOrd for GermanString {
fn partial_cmp(&self, other: &GermanString) -> Option<Ordering> {
Some(self.cmp(other))
}
}
impl Debug for GermanString {
fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
String::from_utf8_lossy(self.as_bytes()).fmt(f)
}
}
#[cfg(test)]
mod tests {
use super::*;
use proptest::prelude::*;
impl Arbitrary for GermanString {
type Parameters = <String as Arbitrary>::Parameters;
type Strategy = BoxedStrategy<Self>;
fn arbitrary_with(args: Self::Parameters) -> Self::Strategy {
any_with::<String>(args)
.prop_map(|s| GermanString::transient(s.as_bytes()))
.boxed()
}
}
#[test]
fn test_empty_string() {
let empty = GermanString::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::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::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"
);
}
proptest! {
#[test]
fn test_roundtrip_vec(input: Vec<u8>) {
let gs = GermanString::transient_from_owned(input.clone());
assert_eq!(input.len(), gs.len(), "length should match");
let out = gs.as_bytes().to_owned();
assert_eq!(input, out, "roundtrip should yield same bytes");
}
#[test]
fn test_roundtrip_string(input: String) {
let gs = GermanString::transient_from_owned(input.clone().into_bytes());
assert_eq!(input.len(), gs.len(), "length should match");
let out = String::from_utf8(gs.as_bytes().to_owned())
.expect("string should be valid after roundtrip");
assert_eq!(input, out, "roundtrip should yield same string");
}
// Test [`Eq`] implementation.
#[test]
fn test_eq(lhs: Vec<u8>, rhs: Vec<u8>) {
let lhs_gs = GermanString::transient(lhs.as_slice());
let rhs_gs = GermanString::transient(rhs.as_slice());
assert_eq!(
(lhs == rhs),
(lhs_gs == rhs_gs),
"Eq should match between std::String and GermanString ({:?} == {:?})",
lhs, rhs,
);
}
#[test]
fn test_reflexivity(x: GermanString) {
prop_assert!(x == x);
}
#[test]
fn test_symmetry(x: GermanString, y: GermanString) {
prop_assert_eq!(x == y, y == x);
}
#[test]
fn test_transitivity(x: GermanString, y: GermanString, z: GermanString) {
if x == y && y == z {
assert!(x == z);
}
}
}
}
