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use rand::{seq::SliceRandom, thread_rng};
use serde::{Deserializer, Serializer};
use sqlx::encode::IsNull;
use sqlx::{Database, Decode, Encode, Type};
use std::fmt;
// Make IDs that:
//
// * Do not require escaping in URLs
// * Do not require escaping in hostnames
// * Are unique up to case conversion
// * Are relatively unlikely to contain cursewords
// * Are relatively unlikely to contain visually similar characters in most
// typefaces
// * Are not sequential
//
// This leaves 23 ASCII characters, or about 4.52 bits of entropy per character
// if generated with uniform probability.
const ALPHABET: [char; 23] = [
'1', '2', '3', '4', '6', '7', '8', '9', 'b', 'c', 'd', 'f', 'h', 'j', 'k', 'n', 'p', 'r', 's',
't', 'w', 'x', 'y',
];
// Pick enough characters per ID to make accidental collisions "acceptably"
// unlikely without also making them _too_ unwieldy. This gives a fraction under
// 68 bits per ID.
const ID_SIZE: usize = 15;
// Intended to be wrapped in a type aliases that specalizes Id on a type that
// implements Prefix, both so that IDs are type-wise distinct within the server
// and so that IDs are readily distinguishable from one another outside of it.
//
// By convention, the prefix should be UPPERCASE - note that the alphabet for
// this is entirely lowercase.
//
// To build a new ID type, create a "marker" type that implements this trait, plus the following list of derives:
//
// ```
// #[derive(Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
// pub struct Person;
//
// impl crate::id::Prefix for Person {
// fn prefix(&self) -> &str {
// "P" // try not to conflict with other prefixes
// }
// }
// ```
//
// Then provide a type alias of the form
//
// ```
// pub type Id = crate::id::Id<Person>;
// ```
//
// The `Id` type will provide a `generate()` method that can generate new random IDs, and the
// resulting type alias can be serialized to and deserialized from strings, and stored in string
// compatible database columns.
#[derive(Clone, Debug, Hash, Eq, Ord, PartialEq, PartialOrd)]
pub struct Id<T>(String, T);
impl<T> fmt::Display for Id<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.0.fmt(f)
}
}
pub trait Prefix {
fn prefix(&self) -> &str;
}
impl<T> Id<T>
where
T: Prefix + Default,
{
pub fn generate() -> Self {
let instance = T::default();
let prefix = instance.prefix();
let random_part = (0..ID_SIZE)
.filter_map(|_| ALPHABET.choose(&mut thread_rng()))
.copied();
let id = prefix.chars().chain(random_part).collect();
Self(id, instance)
}
}
impl<T> serde::ser::Serialize for Id<T> {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
let Self(id, _) = self;
id.serialize(serializer)
}
}
impl<'de, T> serde::de::Deserialize<'de> for Id<T>
where
T: Default,
{
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where
D: Deserializer<'de>,
{
let instance = T::default();
let id = String::deserialize(deserializer)?;
Ok(Self(id, instance))
}
}
// Type is manually implemented so that we can implement Decode to do
// recover the type token on read. Implementation is otherwise based on
// `#[derive(sqlx::Type)]` with the `#[sqlx(transparent)]` attribute.
impl<DB, T> Type<DB> for Id<T>
where
DB: Database,
String: Type<DB>,
{
fn type_info() -> <DB as Database>::TypeInfo {
<String as Type<DB>>::type_info()
}
fn compatible(ty: &<DB as Database>::TypeInfo) -> bool {
<String as Type<DB>>::compatible(ty)
}
}
impl<'r, DB, T> Decode<'r, DB> for Id<T>
where
DB: Database,
String: Decode<'r, DB>,
T: Default,
{
fn decode(value: <DB as Database>::ValueRef<'r>) -> Result<Self, sqlx::error::BoxDynError> {
let instance = T::default();
let id = String::decode(value)?;
Ok(Self(id, instance))
}
}
impl<'q, DB, T> Encode<'q, DB> for Id<T>
where
DB: Database,
String: Encode<'q, DB>,
{
fn encode(
self,
buf: &mut <DB as Database>::ArgumentBuffer<'q>,
) -> Result<IsNull, sqlx::error::BoxDynError> {
let Self(id, _) = self;
id.encode(buf)
}
fn encode_by_ref(
&self,
buf: &mut <DB as Database>::ArgumentBuffer<'q>,
) -> Result<IsNull, sqlx::error::BoxDynError> {
let Self(id, _) = self;
id.encode_by_ref(buf)
}
fn produces(&self) -> Option<<DB as Database>::TypeInfo> {
let Self(id, _) = self;
id.produces()
}
fn size_hint(&self) -> usize {
let Self(id, _) = self;
id.size_hint()
}
}
|
