jsonptr/index.rs
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//! Abstract index representation for RFC 6901.
//!
//! [RFC 6901](https://datatracker.ietf.org/doc/html/rfc6901) defines two valid
//! ways to represent array indices as Pointer tokens: non-negative integers,
//! and the character `-`, which stands for the index after the last existing
//! array member. While attempting to use `-` to resolve an array value will
//! always be out of bounds, the token can be useful when paired with utilities
//! which can mutate a value, such as this crate's [`assign`](crate::assign)
//! functionality or JSON Patch [RFC
//! 6902](https://datatracker.ietf.org/doc/html/rfc6902), as it provides a way
//! to express where to put the new element when extending an array.
//!
//! While this crate doesn't implement RFC 6902, it still must consider
//! non-numerical indices as valid, and provide a mechanism for manipulating
//! them. This is what this module provides.
//!
//! The main use of the `Index` type is when resolving a [`Token`] instance as a
//! concrete index for a given array length:
//!
//! ```
//! # use jsonptr::{index::Index, Token};
//! assert_eq!(Token::new("1").to_index(), Ok(Index::Num(1)));
//! assert_eq!(Token::new("-").to_index(), Ok(Index::Next));
//! assert!(Token::new("a").to_index().is_err());
//!
//! assert_eq!(Index::Num(0).for_len(1), Ok(0));
//! assert!(Index::Num(1).for_len(1).is_err());
//! assert!(Index::Next.for_len(1).is_err());
//!
//! assert_eq!(Index::Num(1).for_len_incl(1), Ok(1));
//! assert_eq!(Index::Next.for_len_incl(1), Ok(1));
//! assert!(Index::Num(2).for_len_incl(1).is_err());
//!
//! assert_eq!(Index::Num(42).for_len_unchecked(30), 42);
//! assert_eq!(Index::Next.for_len_unchecked(30), 30);
//! ```
use crate::Token;
use alloc::string::String;
use core::{fmt, num::ParseIntError, str::FromStr};
/// Represents an abstract index into an array.
///
/// If provided an upper bound with [`Self::for_len`] or [`Self::for_len_incl`],
/// will produce a concrete numerical index.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Index {
/// A non-negative integer value
Num(usize),
/// The `-` token, the position of the next would-be item in the array
Next,
}
impl Index {
/// Bounds the index for a given array length (exclusive).
///
/// The upper range is exclusive, so only indices that are less than
/// the given length will be accepted as valid. This ensures that
/// the resolved numerical index can be used to access an existing array
/// element.
///
/// [`Self::Next`], by consequence, is always considered *invalid*, since
/// it resolves to the array length itself.
///
/// See also [`Self::for_len_incl`] for an alternative if you wish to accept
/// [`Self::Next`] (or its numerical equivalent) as valid.
///
/// # Examples
///
/// ```
/// # use jsonptr::index::Index;
/// assert_eq!(Index::Num(0).for_len(1), Ok(0));
/// assert!(Index::Num(1).for_len(1).is_err());
/// assert!(Index::Next.for_len(1).is_err());
/// ```
/// # Errors
/// Returns [`OutOfBoundsError`] if the index is out of bounds.
pub fn for_len(&self, length: usize) -> Result<usize, OutOfBoundsError> {
match *self {
Self::Num(index) if index < length => Ok(index),
Self::Num(index) => Err(OutOfBoundsError { length, index }),
Self::Next => Err(OutOfBoundsError {
length,
index: length,
}),
}
}
/// Bounds the index for a given array length (inclusive).
///
/// The upper range is inclusive, so an index pointing to the position
/// _after_ the last element will be considered valid. Be careful when using
/// the resulting numerical index for accessing an array.
///
/// [`Self::Next`] is always considered valid.
///
/// See also [`Self::for_len`] for an alternative if you wish to ensure that
/// the resolved index can be used to access an existing array element.
///
/// # Examples
///
/// ```
/// # use jsonptr::index::Index;
/// assert_eq!(Index::Num(1).for_len_incl(1), Ok(1));
/// assert_eq!(Index::Next.for_len_incl(1), Ok(1));
/// assert!(Index::Num(2).for_len_incl(1).is_err());
/// ```
///
/// # Errors
/// Returns [`OutOfBoundsError`] if the index is out of bounds.
pub fn for_len_incl(&self, length: usize) -> Result<usize, OutOfBoundsError> {
match *self {
Self::Num(index) if index <= length => Ok(index),
Self::Num(index) => Err(OutOfBoundsError { length, index }),
Self::Next => Ok(length),
}
}
/// Resolves the index for a given array length.
///
/// No bound checking will take place. If you wish to ensure the
/// index can be used to access an existing element in the array, use
/// [`Self::for_len`] - or use [`Self::for_len_incl`] if you wish to accept
/// [`Self::Next`] as valid as well.
///
/// # Examples
///
/// ```
/// # use jsonptr::index::Index;
/// assert_eq!(Index::Num(42).for_len_unchecked(30), 42);
/// assert_eq!(Index::Next.for_len_unchecked(30), 30);
///
/// // no bounds checks
/// assert_eq!(Index::Num(34).for_len_unchecked(40), 34);
/// assert_eq!(Index::Next.for_len_unchecked(34), 34);
/// ```
pub fn for_len_unchecked(&self, length: usize) -> usize {
match *self {
Self::Num(idx) => idx,
Self::Next => length,
}
}
}
impl fmt::Display for Index {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
match *self {
Self::Num(index) => write!(f, "{index}"),
Self::Next => f.write_str("-"),
}
}
}
impl From<usize> for Index {
fn from(value: usize) -> Self {
Self::Num(value)
}
}
impl FromStr for Index {
type Err = ParseIndexError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
if s == "-" {
Ok(Index::Next)
} else if s.starts_with('0') && s != "0" {
Err(ParseIndexError::LeadingZeros)
} else {
Ok(s.parse::<usize>().map(Index::Num)?)
}
}
}
impl TryFrom<&Token<'_>> for Index {
type Error = ParseIndexError;
fn try_from(value: &Token) -> Result<Self, Self::Error> {
Index::from_str(value.encoded())
}
}
impl TryFrom<&str> for Index {
type Error = ParseIndexError;
fn try_from(value: &str) -> Result<Self, Self::Error> {
Index::from_str(value)
}
}
impl TryFrom<Token<'_>> for Index {
type Error = ParseIndexError;
fn try_from(value: Token) -> Result<Self, Self::Error> {
Index::from_str(value.encoded())
}
}
macro_rules! derive_try_from {
($($t:ty),+ $(,)?) => {
$(
impl TryFrom<$t> for Index {
type Error = ParseIndexError;
fn try_from(value: $t) -> Result<Self, Self::Error> {
Index::from_str(&value)
}
}
)*
}
}
derive_try_from!(String, &String);
/*
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
╔══════════════════════════════════════════════════════════════════════════════╗
║ ║
║ OutOfBoundsError ║
║ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ║
╚══════════════════════════════════════════════════════════════════════════════╝
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
*/
/// Indicates that an `Index` is not within the given bounds.
#[derive(Debug, PartialEq, Eq)]
pub struct OutOfBoundsError {
/// The provided array length.
///
/// If the range is inclusive, the resolved numerical index will be strictly
/// less than this value, otherwise it could be equal to it.
pub length: usize,
/// The resolved numerical index.
///
/// Note that [`Index::Next`] always resolves to the given array length,
/// so it is only valid when the range is inclusive.
pub index: usize,
}
impl fmt::Display for OutOfBoundsError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(
f,
"index {} out of bounds (limit: {})",
self.index, self.length
)
}
}
#[cfg(feature = "std")]
impl std::error::Error for OutOfBoundsError {}
/*
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
╔══════════════════════════════════════════════════════════════════════════════╗
║ ║
║ ParseIndexError ║
║ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ║
╚══════════════════════════════════════════════════════════════════════════════╝
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*/
/// Indicates that the `Token` could not be parsed as valid RFC 6901 index.
#[derive(Debug, PartialEq, Eq)]
pub enum ParseIndexError {
/// The Token does not represent a valid integer.
InvalidInteger(ParseIntError),
/// The Token contains leading zeros.
LeadingZeros,
}
impl From<ParseIntError> for ParseIndexError {
fn from(source: ParseIntError) -> Self {
Self::InvalidInteger(source)
}
}
impl fmt::Display for ParseIndexError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
ParseIndexError::InvalidInteger(source) => {
write!(f, "failed to parse token as an integer: {source}")
}
ParseIndexError::LeadingZeros => write!(
f,
"token contained leading zeros, which are disallowed by RFC 6901"
),
}
}
}
#[cfg(feature = "std")]
impl std::error::Error for ParseIndexError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self {
ParseIndexError::InvalidInteger(source) => Some(source),
ParseIndexError::LeadingZeros => None,
}
}
}
/*
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╔══════════════════════════════════════════════════════════════════════════════╗
║ ║
║ Tests ║
║ ¯¯¯¯¯¯¯ ║
╚══════════════════════════════════════════════════════════════════════════════╝
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
*/
#[cfg(test)]
mod tests {
use super::*;
use crate::Token;
#[test]
fn index_from_usize() {
let index = Index::from(5usize);
assert_eq!(index, Index::Num(5));
}
#[test]
fn index_try_from_token_num() {
let token = Token::new("3");
let index = Index::try_from(&token).unwrap();
assert_eq!(index, Index::Num(3));
}
#[test]
fn index_try_from_token_next() {
let token = Token::new("-");
let index = Index::try_from(&token).unwrap();
assert_eq!(index, Index::Next);
}
#[test]
fn index_try_from_str_num() {
let index = Index::try_from("42").unwrap();
assert_eq!(index, Index::Num(42));
}
#[test]
fn index_try_from_str_next() {
let index = Index::try_from("-").unwrap();
assert_eq!(index, Index::Next);
}
#[test]
fn index_try_from_string_num() {
let index = Index::try_from(String::from("7")).unwrap();
assert_eq!(index, Index::Num(7));
}
#[test]
fn index_try_from_string_next() {
let index = Index::try_from(String::from("-")).unwrap();
assert_eq!(index, Index::Next);
}
#[test]
fn index_for_len_incl_valid() {
assert_eq!(Index::Num(0).for_len_incl(1), Ok(0));
assert_eq!(Index::Next.for_len_incl(2), Ok(2));
}
#[test]
fn index_for_len_incl_out_of_bounds() {
Index::Num(2).for_len_incl(1).unwrap_err();
}
#[test]
fn index_for_len_unchecked() {
assert_eq!(Index::Num(10).for_len_unchecked(5), 10);
assert_eq!(Index::Next.for_len_unchecked(3), 3);
}
#[test]
fn display_index_num() {
let index = Index::Num(5);
assert_eq!(index.to_string(), "5");
}
#[test]
fn display_index_next() {
assert_eq!(Index::Next.to_string(), "-");
}
#[test]
fn for_len() {
assert_eq!(Index::Num(0).for_len(1), Ok(0));
assert!(Index::Num(1).for_len(1).is_err());
assert!(Index::Next.for_len(1).is_err());
}
#[test]
fn out_of_bounds_error_display() {
let err = OutOfBoundsError {
length: 5,
index: 10,
};
assert_eq!(err.to_string(), "index 10 out of bounds (limit: 5)");
}
#[test]
fn parse_index_error_display() {
let err = ParseIndexError::InvalidInteger("not a number".parse::<usize>().unwrap_err());
assert_eq!(
err.to_string(),
"failed to parse token as an integer: invalid digit found in string"
);
assert_eq!(
ParseIndexError::LeadingZeros.to_string(),
"token contained leading zeros, which are disallowed by RFC 6901"
);
}
#[test]
#[cfg(feature = "std")]
fn parse_index_error_source() {
use std::error::Error;
let err = ParseIndexError::InvalidInteger("not a number".parse::<usize>().unwrap_err());
assert_eq!(
err.source().unwrap().to_string(),
"not a number".parse::<usize>().unwrap_err().to_string()
);
assert!(ParseIndexError::LeadingZeros.source().is_none());
}
#[test]
fn try_from_token() {
let token = Token::new("3");
let index = <Index as TryFrom<Token>>::try_from(token).unwrap();
assert_eq!(index, Index::Num(3));
let token = Token::new("-");
let index = Index::try_from(&token).unwrap();
assert_eq!(index, Index::Next);
}
}