keyhog-scanner 0.5.43

keyhog-scanner: high-performance SIMD-accelerated secret detection engine
Documentation 
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//! Unicode-escape decode-through: resolve `\uXXXX` and `\xXX` escapes (plus
//! single-character backslash escapes) before pattern matching.
//!
//! Secrets are frequently embedded as JSON/JS/source-string literals where the
//! interesting bytes hide behind `\u00..`/`\x..` escapes. Decoding them lets the
//! scanner match the literal credential. Shares hex readers and lazy output
//! allocation with the other decoders via [`super::util`].

use super::util::{
    lazy_decoded_prefix, resolve_escaped_codepoint, simple_control_escape, take_hex_digits_indexed,
};

/// Decode backslash escapes (`\uXXXX`, `\xXX`, and `\<char>`) in `input`.
///
/// Returns `Err(())` on a truncated/invalid escape so the caller can skip the
/// candidate rather than emit a corrupted decode.
pub(super) fn unicode_escape_decode(input: &str) -> Result<String, ()> {
    let mut decoded_text: Option<String> = None;
    let mut chars = input.char_indices().peekable();
    while let Some((idx, ch)) = chars.next() {
        if ch != '\\' {
            if let Some(decoded_text) = decoded_text.as_mut() {
                decoded_text.push(ch);
            }
            continue;
        }
        match chars.next().map(|(_, escaped)| escaped) {
            Some('u') => {
                let code = take_hex_digits_indexed(&mut chars, 4)?;
                // Shared surrogate-pair resolution (see `util`): reads the
                // following `\u` low-surrogate code unit itself when `code` is a
                // high surrogate. The `CharIndices` walker is mapped to a `char`
                // iterator so the continuation read reflects on `chars`.
                let resolved =
                    resolve_escaped_codepoint(code, &mut chars.by_ref().map(|(_, c)| c))?;
                lazy_decoded_prefix(&mut decoded_text, input, idx).push(resolved);
            }
            Some('x') => {
                let code = take_hex_digits_indexed(&mut chars, 2)?;
                lazy_decoded_prefix(&mut decoded_text, input, idx)
                    .push(char::from_u32(code).ok_or(())?);
            }
            Some(escaped) => {
                let decoded = match simple_control_escape(escaped) {
                    Some(control) => control,
                    None => escaped,
                };
                lazy_decoded_prefix(&mut decoded_text, input, idx).push(decoded);
            }
            None => return Err(()),
        }
    }
    decoded_text.ok_or(())
}