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storable.rs
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storable.rs
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use std::convert::TryInto;
/// A trait with convenience methods for storing an element into a stable structure.
pub trait Storable {
/// Converts an element into bytes.
///
/// NOTE: `Cow` is used here to avoid unnecessary cloning.
fn to_bytes(&self) -> std::borrow::Cow<[u8]>;
/// Converts bytes into an element.
///
/// NOTE: The bytes are passed as a `Vec<u8>` as opposed to `&[u8]` because
/// in the vast majority of cases, the caller will no longer need the bytes,
/// and passing a `Vec<u8>` prevents unnecessary cloning.
fn from_bytes(bytes: Vec<u8>) -> Self;
}
// NOTE: Below are a few implementations of `Storable` for common types.
// Some of these implementations use `unwrap`, as opposed to returning a `Result`
// with a possible error. The reason behind this decision is that these
// `unwrap`s would be triggered in one of the following cases:
//
// 1) The implementation of `Storable` has a bug.
// 2) The data being stored in the stable structure is corrupt.
//
// Both of these errors are irrecoverable at runtime, and given the additional
// complexity of exposing these errors in the API of stable structures, an `unwrap`
// in case of a detected error is preferable and safer.
impl Storable for () {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Borrowed(&[])
}
fn from_bytes(bytes: Vec<u8>) -> Self {
assert!(bytes.is_empty());
}
}
impl Storable for Vec<u8> {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Borrowed(self)
}
fn from_bytes(bytes: Vec<u8>) -> Self {
bytes
}
}
impl Storable for String {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Borrowed(self.as_bytes())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
String::from_utf8(bytes).unwrap()
}
}
impl Storable for u128 {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Owned(self.to_le_bytes().to_vec())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
Self::from_le_bytes(bytes.try_into().unwrap())
}
}
impl Storable for u64 {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Owned(self.to_le_bytes().to_vec())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
Self::from_le_bytes(bytes.try_into().unwrap())
}
}
impl Storable for u32 {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Owned(self.to_le_bytes().to_vec())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
Self::from_le_bytes(bytes.try_into().unwrap())
}
}
impl Storable for u16 {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Owned(self.to_le_bytes().to_vec())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
Self::from_le_bytes(bytes.try_into().unwrap())
}
}
impl Storable for u8 {
fn to_bytes(&self) -> std::borrow::Cow<[u8]> {
std::borrow::Cow::Owned(self.to_le_bytes().to_vec())
}
fn from_bytes(bytes: Vec<u8>) -> Self {
Self::from_le_bytes(bytes.try_into().unwrap())
}
}