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//! The config module is used to change the behavior of bincode's encoding and decoding logic.
//!
//! *Important* make sure you use the same config for encoding and decoding, or else bincode will not work properly.
//!
//! To use a config, first create a type of [Configuration]. This type will implement trait [Config] for use with bincode.
//!
//! ```
//! let config = bincode::config::standard()
//! // pick one of:
//! .with_big_endian()
//! .with_little_endian()
//! // pick one of:
//! .with_variable_int_encoding()
//! .with_fixed_int_encoding();
//! ```
//!
//! See [Configuration] for more information on the configuration options.
pub(crate) use self::internal::*;
use core::marker::PhantomData;
/// The Configuration struct is used to build bincode configurations. The [Config] trait is implemented
/// by this struct when a valid configuration has been constructed.
///
/// The following methods are mutually exclusive and will overwrite each other. The last call to one of these methods determines the behavior of the configuration:
///
/// - [with_little_endian] and [with_big_endian]
/// - [with_fixed_int_encoding] and [with_variable_int_encoding]
///
///
/// [with_little_endian]: #method.with_little_endian
/// [with_big_endian]: #method.with_big_endian
/// [with_fixed_int_encoding]: #method.with_fixed_int_encoding
/// [with_variable_int_encoding]: #method.with_variable_int_encoding
#[derive(Copy, Clone)]
pub struct Configuration<E = LittleEndian, I = Varint, L = NoLimit> {
_e: PhantomData<E>,
_i: PhantomData<I>,
_l: PhantomData<L>,
}
// When adding more features to configuration, follow these steps:
// - Create 2 or more structs that can be used as a type (e.g. Limit and NoLimit)
// - Add an `Internal...Config` to the `internal` module
// - Make sure `Config` and `impl<T> Config for T` extend from this new trait
// - Add a generic to `Configuration`
// - Add this generic to `impl<...> Default for Configuration<...>`
// - Add this generic to `const fn generate<...>()`
// - Add this generic to _every_ function in `Configuration`
// - Add your new methods
/// The default config for bincode 2.0. By default this will be:
/// - Little endian
/// - Variable int encoding
pub const fn standard() -> Configuration {
generate()
}
/// Creates the "legacy" default config. This is the default config that was present in bincode 1.0
/// - Little endian
/// - Fixed int length encoding
pub const fn legacy() -> Configuration<LittleEndian, Fixint, NoLimit> {
generate()
}
impl<E, I, L> Default for Configuration<E, I, L> {
fn default() -> Self {
generate()
}
}
const fn generate<E, I, L>() -> Configuration<E, I, L> {
Configuration {
_e: PhantomData,
_i: PhantomData,
_l: PhantomData,
}
}
impl<E, I, L> Configuration<E, I, L> {
/// Makes bincode encode all integer types in big endian.
pub const fn with_big_endian(self) -> Configuration<BigEndian, I, L> {
generate()
}
/// Makes bincode encode all integer types in little endian.
pub const fn with_little_endian(self) -> Configuration<LittleEndian, I, L> {
generate()
}
/// Makes bincode encode all integer types with a variable integer encoding.
///
/// Encoding an unsigned integer v (of any type excepting u8) works as follows:
///
/// 1. If `u < 251`, encode it as a single byte with that value.
/// 2. If `251 <= u < 2**16`, encode it as a literal byte 251, followed by a u16 with value `u`.
/// 3. If `2**16 <= u < 2**32`, encode it as a literal byte 252, followed by a u32 with value `u`.
/// 4. If `2**32 <= u < 2**64`, encode it as a literal byte 253, followed by a u64 with value `u`.
/// 5. If `2**64 <= u < 2**128`, encode it as a literal byte 254, followed by a
/// u128 with value `u`.
///
/// Then, for signed integers, we first convert to unsigned using the zigzag algorithm,
/// and then encode them as we do for unsigned integers generally. The reason we use this
/// algorithm is that it encodes those values which are close to zero in less bytes; the
/// obvious algorithm, where we encode the cast values, gives a very large encoding for all
/// negative values.
///
/// The zigzag algorithm is defined as follows:
///
/// ```rust
/// # type Signed = i32;
/// # type Unsigned = u32;
/// fn zigzag(v: Signed) -> Unsigned {
/// match v {
/// 0 => 0,
/// // To avoid the edge case of Signed::min_value()
/// // !n is equal to `-n - 1`, so this is:
/// // !n * 2 + 1 = 2(-n - 1) + 1 = -2n - 2 + 1 = -2n - 1
/// v if v < 0 => !(v as Unsigned) * 2 - 1,
/// v if v > 0 => (v as Unsigned) * 2,
/// # _ => unreachable!()
/// }
/// }
/// ```
///
/// And works such that:
///
/// ```rust
/// # let zigzag = |n: i64| -> u64 {
/// # match n {
/// # 0 => 0,
/// # v if v < 0 => !(v as u64) * 2 + 1,
/// # v if v > 0 => (v as u64) * 2,
/// # _ => unreachable!(),
/// # }
/// # };
/// assert_eq!(zigzag(0), 0);
/// assert_eq!(zigzag(-1), 1);
/// assert_eq!(zigzag(1), 2);
/// assert_eq!(zigzag(-2), 3);
/// assert_eq!(zigzag(2), 4);
/// // etc
/// assert_eq!(zigzag(i64::min_value()), u64::max_value());
/// ```
///
/// Note that u256 and the like are unsupported by this format; if and when they are added to the
/// language, they may be supported via the extension point given by the 255 byte.
pub const fn with_variable_int_encoding(self) -> Configuration<E, Varint, L> {
generate()
}
/// Fixed-size integer encoding.
///
/// * Fixed size integers are encoded directly
/// * Enum discriminants are encoded as u32
/// * Lengths and usize are encoded as u64
pub const fn with_fixed_int_encoding(self) -> Configuration<E, Fixint, L> {
generate()
}
/// Sets the byte limit to `limit`.
pub const fn with_limit<const N: usize>(self) -> Configuration<E, I, Limit<N>> {
generate()
}
/// Clear the byte limit.
pub const fn with_no_limit(self) -> Configuration<E, I, NoLimit> {
generate()
}
}
/// Indicates a type is valid for controlling the bincode configuration
pub trait Config:
InternalEndianConfig + InternalIntEncodingConfig + InternalLimitConfig + Copy + Clone
{
}
impl<T> Config for T where
T: InternalEndianConfig + InternalIntEncodingConfig + InternalLimitConfig + Copy + Clone
{
}
/// Encodes all integer types in big endian.
#[derive(Copy, Clone)]
pub struct BigEndian {}
impl InternalEndianConfig for BigEndian {
const ENDIAN: Endian = Endian::Big;
}
/// Encodes all integer types in little endian.
#[derive(Copy, Clone)]
pub struct LittleEndian {}
impl InternalEndianConfig for LittleEndian {
const ENDIAN: Endian = Endian::Little;
}
/// Use fixed-size integer encoding.
#[derive(Copy, Clone)]
pub struct Fixint {}
impl InternalIntEncodingConfig for Fixint {
const INT_ENCODING: IntEncoding = IntEncoding::Fixed;
}
/// Use variable integer encoding.
#[derive(Copy, Clone)]
pub struct Varint {}
impl InternalIntEncodingConfig for Varint {
const INT_ENCODING: IntEncoding = IntEncoding::Variable;
}
/// Sets an unlimited byte limit.
#[derive(Copy, Clone)]
pub struct NoLimit {}
impl InternalLimitConfig for NoLimit {
const LIMIT: Option<usize> = None;
}
/// Sets the byte limit to N.
#[derive(Copy, Clone)]
pub struct Limit<const N: usize> {}
impl<const N: usize> InternalLimitConfig for Limit<N> {
const LIMIT: Option<usize> = Some(N);
}
mod internal {
use super::Configuration;
pub trait InternalEndianConfig {
const ENDIAN: Endian;
}
impl<E: InternalEndianConfig, I, L> InternalEndianConfig for Configuration<E, I, L> {
const ENDIAN: Endian = E::ENDIAN;
}
#[derive(PartialEq, Eq)]
pub enum Endian {
Little,
Big,
}
pub trait InternalIntEncodingConfig {
const INT_ENCODING: IntEncoding;
}
impl<E, I: InternalIntEncodingConfig, L> InternalIntEncodingConfig for Configuration<E, I, L> {
const INT_ENCODING: IntEncoding = I::INT_ENCODING;
}
#[derive(PartialEq, Eq)]
pub enum IntEncoding {
Fixed,
Variable,
}
pub trait InternalLimitConfig {
const LIMIT: Option<usize>;
}
impl<E, I, L: InternalLimitConfig> InternalLimitConfig for Configuration<E, I, L> {
const LIMIT: Option<usize> = L::LIMIT;
}
}