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#![warn(clippy::all)]
#![warn(clippy::pedantic)]
#![warn(clippy::cargo)]
#![warn(missing_copy_implementations)]
#![warn(missing_debug_implementations)]
#![warn(trivial_casts, trivial_numeric_casts)]
#![warn(unused_qualifications)]
#![warn(variant_size_differences)]
#![forbid(unsafe_code)]
#![warn(missing_docs)]
#![allow(clippy::multiple_crate_versions)]
#![doc = include_str!("../README.md")]
#[doc(no_inline)] // https://users.rust-lang.org/t/re-exporting-type-and-rustdoc/50847
pub use ascii::AsciiChar;
use itertools::Itertools;
use std::{cmp::Ordering, error::Error, fmt::Display, ops::Range};
/// Main type to perform binary search through.
///
/// This type upholds the important invariants of [`SortedString::binary_search()`]:
///
/// - a *sorted* string is required,
/// - as well as some [`AsciiChar`] separator to split by.
///
/// Access to binary search is gated behind this type. For this to not be too painful,
/// the type is designed to be cheap, as it doesn't own the potentially large haystack
/// to perform binary search on.
///
/// The terms *haystack* and *needle* are used here as they are in
/// [`std::str::pattern`].
///
/// # Instance Creation
///
/// There are two avenues:
///
/// 1. [`SortedString::new_checked()`]: recommended, ensuring soundness
/// 2. [`SortedString::new_unchecked()`]: unsafe, faster
///
/// ## Note on ASCII requirement
///
/// On instance creation, the separator has to be [within the ASCII
/// range](https://doc.rust-lang.org/std/primitive.char.html#method.is_ascii). In other
/// words, **multi-byte (in the sense of UTF-8) separators are not supported**. This
/// leaves common separators like `\n`, `\t`, `-`, `,` and [many more][ascii::AsciiChar]
/// available, while arbitrary [`char`]s are not allowed:
///
/// ```compile_fail
/// let sep = '🦀';
/// let haystack = "a,b,c";
/// // Not allowed:
/// let _ = b4s::SortedString::new_checked(haystack, sep);
/// ```
///
/// UTF-8 being a variable-length encoding, allowing *any* separator [`char`] would
/// require an initial [linear scan of the input
/// string](https://doc.rust-lang.org/std/primitive.str.html#method.char_indices):
///
/// - either at instance creation time, then saving the results,
/// - or before each search.
///
/// The former takes up a lot of space ([`usize`] pointers, which on 64-bit are much
/// larger than the separator itself), the latter time. Both are undesirable. Even more
/// undesirable would be handling UTF-8 parsing and validation manually. The ASCII
/// requirement [keeps things simple](https://en.wikipedia.org/wiki/KISS_principle) and
/// is unlikely to be an impediment in real-world use.
///
/// As UTF-8 is fully ASCII-compatible, allowing only that means the string can be
/// efficiently scanned as bytes. The needle and haystack can still be any UTF-8 string.
/// No multi-byte code point (with its continuation bytes) [contains bytes in the ASCII
/// range](https://en.wikipedia.org/wiki/UTF-8#Encoding). Scanning for such an ASCII
/// separator is therefore sound:
///
/// - it won't be found at [non-char
/// boundaries](https://doc.rust-lang.org/std/primitive.str.html#method.is_char_boundary),
/// - and it itself will be a boundary.
///
/// These properties simplify scanning and allow it to be fast at both instance creation
/// and search time. The downside is hopefully negligible and in the common case
/// unnoticeable. Please contact the author if your use case requires multi-byte
/// support.
///
/// The ASCII requirement is manifested in the [type
/// system](https://dusted.codes/the-type-system-is-a-programmers-best-friend),
/// enforcing correct usage [at compile time](https://cliffle.com/blog/rust-typestate/).
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct SortedString<'a> {
string: &'a str,
sep: AsciiChar,
}
impl Display for SortedString<'_> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "SortedString({:?}, {:?})", self.string, self.sep)
}
}
/// Error returned in case of a failed search.
///
/// [Thin wrapper](https://doc.rust-lang.org/rust-by-example/generics/new_types.html)
/// for [`Range<usize>`], required to implement [`Error`], achieving a [useful
/// API](https://rust-lang.github.io/api-guidelines/interoperability.html#error-types-are-meaningful-and-well-behaved-c-good-err).
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct SearchError(
/// Location of the last *unsuccessful* comparison.
///
/// This is *not* the location where the needle could be inserted. That location is
/// either to the left *or* right of this location, depending on how
/// [comparison](https://doc.rust-lang.org/std/primitive.str.html#impl-PartialOrd%3Cstr%3E-for-str)
/// goes. As this error is not particularly actionable at runtime, the exact
/// location (left, right) is not reported, saving computation at runtime and
/// affording a simpler implementation.
pub Range<usize>,
);
impl Error for SearchError {}
impl Display for SearchError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let SearchError(range) = self;
write!(f, "needle not found, last looked at {range:?}")
}
}
/// The result of a [`SortedString::binary_search()`].
///
///
/// ## Success case
///
/// The location where the match was found.
///
/// ## Error case
///
/// Refer to [`SearchError`] for details.
pub type SearchResult = Result<Range<usize>, SearchError>;
impl<'a> SortedString<'a> {
/// Creates a new instance of [`SortedString`], performing sanity checks.
///
/// See [`SortedString::new_unchecked()`] for a version without checks.
///
/// The performed checks and failure modes are outlined in the [error
/// examples](#errors) below.
///
/// # Example
///
/// ```
/// let sep = b4s::AsciiChar::Comma;
/// let haystack = "a,b,c";
/// let sorted_string = b4s::SortedString::new_checked(haystack, sep);
///
/// assert!(sorted_string.is_ok());
/// ```
///
/// # Errors
///
/// This method returns a [`SortedStringCreationError`] in the cases outlined below.
///
/// ## Example: Creation Fails (Haystack Not Sorted)
///
/// Binary search requires prior sorting, so creation has to fail.
///
/// ```
/// let sep = b4s::AsciiChar::Comma;
/// let unsorted_haystack = "a,c,b";
/// let sorted_string = b4s::SortedString::new_checked(unsorted_haystack, sep);
///
/// assert_eq!(sorted_string, Err(b4s::SortedStringCreationError::NotSorted));
/// ```
///
/// This error might also creep in when passing a newline-separated file containing
/// a trailing newline. The empty string will be in last position, contradicting
/// sorting.
///
/// ```
/// let sep = b4s::AsciiChar::LineFeed;
/// let haystack = "Aachen\nAmpel\nAngel\nApfel\n";
/// let ss = b4s::SortedString::new_checked(haystack, sep);
///
/// assert_eq!(ss, Err(b4s::SortedStringCreationError::NotSorted));
/// ```
///
/// ## Example: Creation Fails (Haystack Empty)
///
/// Supplying an empty haystack [`str`] is likely an error and therefore fails.
///
/// ```
/// let sep = b4s::AsciiChar::Comma;
/// let haystack = "";
/// let sorted_string = b4s::SortedString::new_checked(haystack, sep);
///
/// assert_eq!(sorted_string, Err(b4s::SortedStringCreationError::EmptyHaystack));
/// ```
pub fn new_checked(
haystack: &'a str,
sep: AsciiChar,
) -> Result<Self, SortedStringCreationError> {
if haystack.is_empty() {
return Err(SortedStringCreationError::EmptyHaystack);
}
let sorted_string = Self::new(haystack, sep);
if sorted_string.is_sorted() {
Ok(sorted_string)
} else {
Err(SortedStringCreationError::NotSorted)
}
}
/// Searches for a needle inside this [`SortedString`].
///
/// The return type aims to imitate [`binary_search` of the standard
/// library](https://doc.rust-lang.org/std/primitive.slice.html#method.binary_search),
/// returning a [`Result`]. The success case is a [`std::ops::Range`], not a single
/// [`usize`], as the haystack is variable-length. For the error case, see below.
///
/// # Examples
///
/// For common examples, see the [crate-level documentation](crate). The following
/// are more specific examples.
///
/// ## Multi-byte needle and haystack
///
/// The needle and haystack can be *any* UTF-8 string. However, note that the
/// returned [`Range`] is returned in raw byte positions, similar to
/// [`std::str::len`](https://doc.rust-lang.org/std/primitive.str.html#method.len):
///
/// > This length is in bytes, not chars or graphemes. In other words, it might not
/// > be what a human considers the length of the string.
///
/// ```
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// let sep = b4s::AsciiChar::VerticalBar;
/// let haystack = "Apfel|Bäume|Zäune|zäunen|Äpfel|Öfen|ƒoo|مرحبًا|你好|😂";
/// let ss = b4s::SortedString::new_checked(haystack, sep)?;
///
/// let needle = "Bäume";
/// let result = ss.binary_search(needle);
///
/// assert_eq!(result, Ok(std::ops::Range { start: 6, end: 12 }));
/// # Ok(())
/// # }
/// ```
///
/// ## Needle contains separator
///
/// This situation not handled specially. Such needles will be impossible to find:
///
/// ```
/// use std::{error::Error, ops::Range};
///
/// fn main() -> Result<(), Box<dyn Error>> {
/// let sep = b4s::AsciiChar::A;
/// let haystack = "Aachen\nAmpel\nAngel\nApfel\n";
/// let ss = b4s::SortedString::new_checked(haystack, sep)?;
///
/// let needle = "Angel";
/// let result = ss.binary_search(needle);
/// assert_eq!(result, Err(b4s::SearchError(Range { start: 0, end: 0 })));
///
/// let needle = "ngel\n";
/// let range = ss.binary_search(needle)?; // Works (note ? operator also works)
/// assert_eq!(range, Range { start: 14, end: 19 });
///
/// Ok(())
/// }
/// ```
///
/// # Errors
///
/// Refer to [`SearchError`] for more info.
///
/// # Panics
///
/// This method panics when slicing into the `haystack` fails. Occurrences of such
/// panics are [logic
/// bugs](https://doc.rust-lang.org/book/ch09-03-to-panic-or-not-to-panic.html#cases-in-which-you-have-more-information-than-the-compiler)
/// and should never occur (see the below assumptions). Please report them if they
/// do.
///
/// The panic allows the API to be simple. No panic implies converting the failure
/// to some error value, like an `enum`. That `enum` would then have a variant such
/// as `EncodingError`. However, the user would have no sensible way of handling
/// that, either, and might as well panic anyway. Keeping the panic inside the
/// function allows the return type to be very simple (no `enum` required).
///
/// See also [this
/// thread](https://web.archive.org/web/20230610095730/https://old.reddit.com/r/rust/comments/we33nd/when_is_unwrap_idiomatic/iinvqqh/?context=3),
/// where people who know what they're talking about in terms of Rust
/// ([matklad](https://github.com/matklad),
/// [BurntSushi](https://github.com/BurntSushi)) argue in a similar fashion. The
/// author [took their
/// advice](https://en.wikipedia.org/wiki/Argument_from_authority) to gauge
/// idiomaticity.
///
/// ## Background
///
/// Fundamental assumptions for panic-freedom are:
///
/// - The haystack is `&str`, aka valid UTF-8. **Users cannot pass malformed
/// UTF-8.**
/// - The separator is ASCII, as ensured by signatures working off [`AsciiChar`],
/// providing [type-level
/// guarantees](https://rust-lang.github.io/api-guidelines/dependability.html#static-enforcement).
/// **Users can only pass single-byte UTF-8 values.**
/// - The separator being ASCII ([highest bit
/// 0](https://en.wikipedia.org/wiki/ASCII#8-bit_codes)), it cannot be part of any
/// code point encoded as [multiple bytes using UTF-8 (highest bit
/// 1)](https://en.wikipedia.org/wiki/UTF-8#Encoding), as
/// [validated](https://doc.rust-lang.org/std/primitive.char.html#validity) in
/// this sanity check:
///
/// ```
/// for code_point in 0..=0x10FFFF {
/// if let Some(c) = std::char::from_u32(code_point) {
/// if c.is_ascii() {
/// continue;
/// }
/// for byte in c.to_string().bytes() {
/// assert!(!byte.is_ascii());
/// }
/// }
/// }
/// ```
/// - *Single*-byte values with highest bit 1 are outside the ASCII range and
/// **invalid UTF-8**:
///
/// ```
/// for byte in 0x80u8..=0xFFu8 {
/// assert!(!byte.is_ascii());
/// assert!(std::str::from_utf8(&[byte]).is_err());
/// }
/// ```
///
/// ### Fuzz Testing
///
/// To further strengthen confidence in panic-freedom, fuzz testing was conducted
/// using [`afl`](https://crates.io/crates/afl).
///
/// If you have access to the crate's source code repository, run fuzz testing
/// yourself from the root using
///
/// ```bash
/// cargo install just && just fuzz
/// ```
///
/// The author let a fuzz test run for over 5 billion iterations, finding no panics:
///
/// ```text
/// american fuzzy lop ++4.06c {default} (target/debug/afl-target) [fast]
/// ┌─ process timing ────────────────────────────────────┬─ overall results ────┐
/// │ run time : 0 days, 19 hrs, 7 min, 6 sec │ cycles done : 192k │
/// │ last new find : 0 days, 18 hrs, 56 min, 54 sec │ corpus count : 39 │
/// │last saved crash : none seen yet │saved crashes : 0 │
/// │ last saved hang : none seen yet │ saved hangs : 0 │
/// ├─ cycle progress ─────────────────────┬─ map coverage┴──────────────────────┤
/// │ now processing : 31.444679 (79.5%) │ map density : 3.31% / 6.22% │
/// │ runs timed out : 0 (0.00%) │ count coverage : 2.77 bits/tuple │
/// ├─ stage progress ─────────────────────┼─ findings in depth ─────────────────┤
/// │ now trying : splice 8 │ favored items : 12 (30.77%) │
/// │ stage execs : 27/28 (96.43%) │ new edges on : 14 (35.90%) │
/// │ total execs : 5.15G │ total crashes : 0 (0 saved) │
/// │ exec speed : 73.5k/sec │ total tmouts : 2 (0 saved) │
/// ├─ fuzzing strategy yields ────────────┴─────────────┬─ item geometry ───────┤
/// │ bit flips : disabled (default, enable with -D) │ levels : 6 │
/// │ byte flips : disabled (default, enable with -D) │ pending : 0 │
/// │ arithmetics : disabled (default, enable with -D) │ pend fav : 0 │
/// │ known ints : disabled (default, enable with -D) │ own finds : 33 │
/// │ dictionary : n/a │ imported : 0 │
/// │havoc/splice : 31/1.98G, 2/3.17G │ stability : 100.00% │
/// │py/custom/rq : unused, unused, 0/1126, 0/19.4k ├───────────────────────┘
/// │ trim/eff : 1.58%/6355, disabled │ [cpu003: 12%]
/// └────────────────────────────────────────────────────┘
/// ```
///
/// Note: at the time of writing,
/// [`cargo-fuzz`](https://github.com/rust-fuzz/cargo-fuzz) and
/// [`cargo-afl`](https://github.com/rust-fuzz/afl.rs) were available. The former
/// currently only wraps [`libFuzzer`](https://llvm.org/docs/LibFuzzer.html), the
/// latter works with [`afl`](https://github.com/google/AFL). **Both were already
/// deprecated** at the time of writing, but continue to work well. `afl` was chosen
/// as it didn't require a nightly toolchain.
pub fn binary_search<U>(&self, needle: U) -> SearchResult
where
U: AsRef<str>,
{
let haystack = self.string;
let needle = needle.as_ref();
let leftmost = 0;
let rightmost = haystack.len();
let mut low = leftmost;
let mut high = rightmost;
let mut start = leftmost;
let mut end = rightmost;
let haystack = haystack.as_bytes();
let pred = |c: &&u8| **c == self.sep.as_byte();
while low < high {
let mid = low + (high - low) / 2;
start = match haystack[..mid].iter().rev().find_position(pred) {
Some((delta, _)) => mid - delta,
None => leftmost,
};
end = match haystack[mid..].iter().find_position(pred) {
Some((delta, _)) => mid + delta,
None => rightmost,
};
let haystack_word = std::str::from_utf8(&haystack[start..end])
.expect("Indices aren't valid for slicing into haystack. They are at ASCII chars and therefore always assumed valid.");
match needle.cmp(haystack_word) {
Ordering::Less => high = mid.saturating_sub(1),
Ordering::Equal => return Ok(Range { start, end }),
Ordering::Greater => low = mid + 1,
}
}
Err(SearchError(Range { start, end }))
}
/// Creates an instance of [`SortedString`] [without performing sanity
/// checks](https://rust-lang.github.io/api-guidelines/dependability.html#dynamic-enforcement-with-opt-out).
///
/// This is essentially what conventionally would be a simple
/// [`new()`](https://rust-lang.github.io/api-guidelines/interoperability.html#types-eagerly-implement-common-traits-c-common-traits),
/// but specifically named to alert users to the dangers.
///
/// # Example: Simple Use
///
/// ```
/// let sep = b4s::AsciiChar::Comma;
/// let haystack = "a,b,c";
/// let sorted_string = b4s::SortedString::new_unchecked(haystack, sep);
/// ```
///
/// # Example: Incorrect Use
///
/// ```
/// use std::ops::Range;
///
/// let sep = b4s::AsciiChar::Comma;
/// let unsorted_haystack = "a,c,b";
/// let sorted_string = b4s::SortedString::new_unchecked(unsorted_haystack, sep);
///
/// // Unable to find element in unsorted haystack
/// assert_eq!(
/// sorted_string.binary_search("b"),
/// Err(b4s::SearchError(Range { start: 0, end: 1 }))
/// );
/// ```
#[must_use]
pub const fn new_unchecked(string: &'a str, sep: AsciiChar) -> Self {
Self::new(string, sep)
}
/// Convenience method to sort a [`str`] by a given separator, returning an owned
/// version.
///
/// As [`SortedString`] is designed to be thin and doesn't own its data (expect for
/// the `sep`), this convenience method helps creating a sorted [`String`] in the
/// required format.
///
/// # Example
///
/// ```
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// let sep = b4s::AsciiChar::LineFeed;
/// // Perhaps this was read directly from a file, where sorting is unreliable/unknown.
/// let unsorted_haystack = "c\nb\na";
/// let sorted_haystack = b4s::SortedString::sort(unsorted_haystack, sep);
///
/// // Passes fine
/// let sorted_string = b4s::SortedString::new_checked(&sorted_haystack, sep)?;
///
/// assert_eq!(
/// sorted_string.binary_search("c"),
/// Ok(std::ops::Range { start: 4, end: 5 })
/// );
/// # Ok(())
/// # }
/// ```
#[must_use]
pub fn sort(string: &str, sep: AsciiChar) -> String {
string
.split(sep.as_char())
.sorted()
.collect::<Vec<&str>>()
.join(&sep.to_string())
}
const fn new(string: &'a str, sep: AsciiChar) -> Self {
Self { string, sep }
}
fn is_sorted(&self) -> bool {
self.string
.split(self.sep.as_char())
.tuple_windows()
.all(|(a, b)| a <= b)
}
}
/// Error that can occur when creating a [`SortedString`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum SortedStringCreationError {
/// The passed haystack was not sorted.
NotSorted,
/// The passed haystack was empty.
EmptyHaystack,
}
impl Error for SortedStringCreationError {}
impl Display for SortedStringCreationError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::NotSorted => write!(f, "The provided string is not sorted."),
Self::EmptyHaystack => write!(f, "The provided string is empty."),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use rstest::rstest;
use std::error::Error;
/// Pretty useless test; just have it so removing `Error` is flagged and would be
/// noticed.
#[rstest]
#[case(Box::new(SortedStringCreationError::NotSorted))]
#[case(Box::new(SortedStringCreationError::EmptyHaystack))]
#[case(Box::new(SearchError(Range { start: 0, end: 1 })))]
fn test_error_trait_implementations_are_present(#[case] err: Box<dyn Error>) {
assert!(!err.to_string().is_empty());
}
}