scalar_types/lib.rs
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//! This library was created to assist with parsing endian sensitive content.
//! It allows us to parse the data normally as though it was native endianness.
//! Then when we need the value we can cast the value to the desired endianness.
//!
//! This saves us from having to create conditional parsing using T::from_xx_bytes,
//! and instead allows us to lazily parse the values. then convert them when we need them.
//! this acts kinda like a endian "superposition".
//!
//! Since this also wraps all the basic scalar types, it gives us a common type
//! to pass to functions that tags the data as endian sensitive.
//!
//! Also included are helper functions to make loading values from a stream quicker.
//!
//! Let's look at a basic use case. We have a file that could of been created on
//! a big or little endian system. The implementation of the file specification
//! states the first byte in the file will signal if the rest of the file is
//! big or little endian. Let's say 0x00 for little endian, and 0x01 for big.
//!
//! Let's create a program that parses the first byte and stores the endianness
//! of the file. Then using that endianness cast a value read from the file.
//!
//! ```
//! use scalar_types::Endian;
//! use std::io::{BufReader, Result};
//!
//! fn read_some_stuff() -> Result<()> {
//! // Binary file contains 01 | 00 00 00 02 .. ..
//! // Big Endian Flag-^ ^-Big Endian 0x2
//! // System endianness is little endian
//! let file = std::fs::File::open("file.bin")?;
//! let mut reader = BufReader::new(file);
//!
//! // File endianness changes based on system that made it
//! // The first byte in the file determines the endianness;
//! // 0 = little, 1 = big
//! let mut buffer = vec![0u8];
//! reader.read_exact(&mut buffer)?;
//!
//! // We can then store the endianness as a variable
//! // and use this to cast. Allowing us to dynamically
//! // cast the data based on the content of the file
//! let endianness = {
//! if buffer[0] == 0 {
//! Endian::Little(())
//! } else {
//! Endian::Big(())
//! }
//! };
//!
//! // Try and read the endian sensitive content normally from stream
//! // Endian values are Endian::Native by default
//! let endian_value = Endian::<u32>::from_stream(&mut reader);
//! let parsed_value = match endian_value {
//! Some(value) => value,
//! None => panic!("Unable to parse value from stream!")
//! };
//!
//! // Then we convert the value only when we need it.
//! // Saving us from having to cast u32::from_xx_bytes for every value
//! let expanded_value = match parsed_value.cast(endianness) {
//! Some(value) => value,
//! None => 0u32
//! };
//!
//! assert_eq!(expanded_value, 2);
//! Ok(())
//! }
//! ```
//!
//! We can also work the other way around! Let's create the file we just parsed
//! by using Endian. We could easily use to_le_bytes and to_be_bytes;
//! however, doing so would mean we need to alternate between the two depending on
//! the system we're targeting. Instead, we can just store the target endianness and use the
//! same code. Dynamically switching the endianness with a stored variable instead.
//! This is a lot cleaner.
//!
//! Instead of using to_le_bytes or to_be_bytes; we'll
//! call the to_ne_bytes, and let Endian handle the converting.
//!
//! ```
//! use scalar_types::Endian;
//! use std::io::{Result, Write};
//! use std::fs::File;
//! use std::path::Path;
//! fn write_some_stuff() -> Result<()> {
//! // Open a file hand for our output
//! let mut output = File::create(Path::new("file.bin"))?;
//!
//! // since we're a little endian system, writing a big endian file
//! // we will assign this value explicitly.
//! // let's store this for later to use it to cast
//! let endianness = Endian::Big(());
//!
//! // Note that Endian::Native isn't actually aware of the system endianness,
//! // it instead acts as an abstract container like a "superposition".
//! // If we wanted to get our native endianness "get_native_endianness()"
//! // is a helper function that will return the correct endianness.
//! // let endianness = get_native_endianness()?;
//!
//! // Moving forward:
//! // Our spec says we need to write 0x01 for big endian, or 0x00 for little.
//! if endianness.is_big() {
//! write!(output, "\x01")?;
//! } else {
//! write!(output, "\x00")?;
//! };
//!
//! // Next we're going to create our native endian 0x02 value
//! let endian_value = Endian::new(2u32);
//!
//! // Finally we write the output
//! if let Some(value) = endian_value.cast(endianness) {
//! // We've already handled endianness, so we will use the built-in to_ne_bytes function
//! output.write(&value.to_ne_bytes())?;
//! }
//!
//! Ok(())
//! }
//! ```
//!
//! This was created to assist me with creating modding tools for video games. As some games share the same
//! data, but the endianness changes based off the console it was built for. Working this way allows me to
//! use the same code for all systems, and cast the values to the native endianness dynamically when needed.
//! I figured I would share it on the off chance other people may find it useful.
/// This error shouldn't really be possible, but out of abundance of caution it has been included.
pub enum Error {
UnknownArchitecture
}
/// Get's the systems native endianness
pub fn get_native_endianness() -> Result<Endian<()>, Error> {
union SharedMemory {
value: u16,
array: [u8; 2]
}
unsafe {
let endian_tester = SharedMemory { value: 0x1234 };
match endian_tester.array[0] {
0x34 => Ok(Endian::Little(())),
0x12 => Ok(Endian::Big(())),
_ => Err(Error::UnknownArchitecture) // Shouldn't be possible, but out of abundance of caution
}
}
}
/// Endian
/// This wraps a scalar value and specializes the value for a specific endianness.
/// In doing so it allows us to tag endian sensitive content, and safely pass it between functions
/// for applications that may require this.
#[derive(Debug)]
#[derive(PartialEq)]
pub enum Endian<T> {
Little(T),
Big(T),
Native(T)
}
/// UNSAFE
/// Swap the endianness of a value by casting the value's memory
/// to a slice and reversing the slice.
///
/// Marked unsafe as it uses a raw pointer; however,
/// the unsafe code is bounded by the size of the variable
/// and should never reach unowned memory.
fn endian_swap_unsafe<DataT>(mut value: DataT) -> DataT {
let ptr: *mut DataT = &mut value;
let array = unsafe { std::slice::from_raw_parts_mut(ptr as *mut u8, std::mem::size_of_val(&value)) };
array.reverse();
value
}
impl<T: Copy + Default> Endian<T> {
/// All values are read in as "Endian::Native(T)". It can be converted between to the desired endianness when needed.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::new(42u16);
/// }
/// ```
pub fn new(value: T) -> Endian<T> {
Endian::Native(value)
}
/// UNSAFE
///
/// Reads and returns a Endian::Native(T) from any type that implements the std:io::Read trait.
/// Advances the stream by the size of type T bytes.
///
/// Marked unsafe as it uses a raw pointer; however,
/// the unsafe code is bounded by the size of the variable
/// and should never reach unowned memory.
/// ```
/// use scalar_types::Endian;
/// use std::io::{BufReader, Result};
///
/// fn read_some_stuff() -> Result<()> {
/// let file = std::fs::File::open("file.bin")?;
/// let mut reader = BufReader::new(file);
///
/// let endian_value = Endian::<u32>::from_stream(&mut reader);
/// let parsed_value = match endian_value {
/// Some(value) => value,
/// None => panic!("Unable to parse value from stream!")
/// };
/// Ok(())
/// }
/// ```
pub fn from_stream<StreamT: std::io::Read>(stream: &mut StreamT) -> Option<Endian<T>> {
let mut value = T::default();
let ptr: *mut T = &mut value;
let buffer = unsafe { std::slice::from_raw_parts_mut(ptr as *mut u8, std::mem::size_of_val(&value)) };
match stream.read_exact(buffer) {
Err(_) => None,
Ok(()) => Some(Endian::Native(value))
}
}
/// Attempts to cast the value held by Endian to a big endian value.
/// Only fail condition is if get_native_endianness fails somehow
///
/// This shouldn't really be possible; however, it does call unsafe.
/// so, out of abundance of caution we include the fail condition.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::new(42u16);
///
/// let be_scalar_types = match scalar_types.as_big() {
/// Some(value) => value,
/// None => panic!("Unable to convert endianness!")
/// };
/// }
/// ```
pub fn as_big(&self) -> Option<T> {
match self {
Endian::Little(value) => Some(endian_swap_unsafe(*value)),
Endian::Big(value) => Some(*value),
Endian::Native(value) => {
match get_native_endianness() {
Err(_) => None,
Ok(order) => match order {
Endian::Little(()) => Some(endian_swap_unsafe(*value)),
Endian::Big(()) => Some(*value),
// Native Endianness being "Native" infinitely recursive
Endian::Native(()) => None
}
}
}
}
}
/// Attempts to cast the value held by Endian to a little endian value.
/// Only fail condition is if get_native_endianness fails somehow
///
/// This shouldn't really be possible; however, it does call unsafe.
/// so, out of abundance of caution we include the fail condition.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::new(42u16);
///
/// let le_scalar_types = match scalar_types.as_little() {
/// Some(value) => value,
/// None => panic!("Unable to convert endianness!")
/// };
/// }
/// ```
pub fn as_little(&self) -> Option<T> {
match self {
Endian::Little(value) => Some(*value),
Endian::Big(value) => Some(endian_swap_unsafe(*value)),
Endian::Native(value) => {
match get_native_endianness() {
Err(_) => None,
Ok(order) => match order {
Endian::Little(()) => Some(*value),
Endian::Big(()) => Some(endian_swap_unsafe(*value)),
// Native Endianness being "Native" infinitely recursive
Endian::Native(()) => None
}
}
}
}
}
/// Attempts to cast the value held by Endian to a native endian value.
/// Only fail condition is if get_native_endianness fails somehow
///
/// This shouldn't really be possible; however, it does call unsafe.
/// so, out of abundance of caution we include the fail condition.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::new(42u16);
///
/// let le_scalar_types = match scalar_types.as_native() {
/// Some(value) => value,
/// None => panic!("Unable to convert endianness!")
/// };
/// }
/// ```
pub fn as_native(&self) -> Option<T> {
match self {
Endian::Little(value) => match get_native_endianness() {
Err(_) => None,
Ok(order) => match order {
Endian::Little(()) => Some(*value),
Endian::Big(()) => Some(endian_swap_unsafe(*value)),
// Native Endianness being "Native" infinitely recursive
Endian::Native(()) => None
}
}
Endian::Big(value) => {
match get_native_endianness() {
Err(_) => None,
Ok(order) => match order {
Endian::Little(()) => Some(endian_swap_unsafe(*value)),
Endian::Big(()) => Some(*value),
// Native Endianness being "Native" infinitely recursive
Endian::Native(()) => None
}
}
}
Endian::Native(value) => Some(*value),
}
}
/// Attempts to cast the value held by Endian to a specified endianness
/// Only fail condition is if get_native_endianness fails somehow
///
/// This shouldn't really be possible; however, it does call unsafe.
/// so, out of abundance of caution we include the fail condition.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::new(42u16);
///
/// let le_scalar_types = scalar_types.cast(Endian::Little(()));
/// let be_scalar_types = scalar_types.cast(Endian::Big(()));
/// let ne_scalar_types = scalar_types.cast(Endian::Native(()));
/// }
/// ```
pub fn cast(&self, order: Endian<()>) -> Option<T> {
match order {
Endian::Little(()) => self.as_little(),
Endian::Big(()) => self.as_big(),
Endian::Native(()) => self.as_native()
}
}
// Returns true if Endian is a Endian::Little option
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::Little(42u16);
///
/// assert_eq!(scalar_types.is_little(), true)
/// }
/// ```
pub fn is_little(&self) -> bool {
match self {
Endian::Little(_) => true,
Endian::Big(_) => false,
Endian::Native(_) => false
}
}
// Returns true if Endian is a Endian::Big option
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// let scalar_types = Endian::Big(42u16);
///
/// assert_eq!(scalar_types.is_big(), true)
/// }
/// ```
pub fn is_big(&self) -> bool {
match self {
Endian::Little(_) => false,
Endian::Big(_) => true,
Endian::Native(_) => false
}
}
// Returns true if Endian is a Endian::Native option
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// // new() creates a Endian::Native
/// let scalar_types = Endian::new(42u16);
/// let ne_scalar_types = Endian::Native(42u16);
///
/// assert_eq!(scalar_types.is_native(), true);
/// assert_eq!(ne_scalar_types.is_native(), true);
/// }
/// ```
pub fn is_native(&self) -> bool {
match self {
Endian::Little(_) => false,
Endian::Big(_) => false,
Endian::Native(_) => true
}
}
/// Unpack the value as a native endian value.
/// If casting fails, the default value for the type is returned instead
/// Not recommended for production.
/// ```
/// use scalar_types::Endian;
/// fn main() {
/// // new() creates a Endian::Native
/// let scalar_types = Endian::new(42u16);
///
/// println!("the meaning of life the universe and everything: {}", scalar_types.unpack());
/// }
/// ```
/// Output:
/// ```
/// "the meaning of life the universe and everything: 42"
/// ```
pub fn unpack(&self) -> T {
if let Some(value) = self.as_native() {
return value;
}
T::default()
}
}