provenant/license_detection/
hash_match.rs

1// SPDX-FileCopyrightText: Provenant contributors
2// SPDX-License-Identifier: Apache-2.0
3
4//! Hash-based exact matching for license detection.
5//!
6//! This module implements the hash matching strategy which computes a hash of the
7//! entire query token sequence and looks for exact matches in the index.
8
9use sha1::{Digest, Sha1};
10
11use crate::license_detection::index::LicenseIndex;
12use crate::license_detection::index::dictionary::{TokenId, TokenKind};
13use crate::license_detection::models::position_span::PositionSpan;
14use crate::license_detection::models::{LicenseMatch, MatchCoordinates, MatcherKind};
15use crate::license_detection::query::QueryRun;
16use crate::models::LineNumber;
17use crate::models::MatchScore;
18
19pub const MATCH_HASH: MatcherKind = MatcherKind::Hash;
20
21/// Compute a SHA1 hash of a token sequence.
22///
23/// Converts token IDs to signed 16-bit integers (matching Python's `array('h')`),
24/// serializes them as little-endian bytes, and computes the SHA1 hash.
25///
26/// # Arguments
27/// * `tokens` - Slice of token IDs
28///
29/// # Returns
30/// 20-byte SHA1 digest
31///
32/// Corresponds to Python: `tokens_hash()` (lines 44-49)
33pub fn compute_hash(tokens: &[TokenId]) -> [u8; 20] {
34    let mut hasher = Sha1::new();
35
36    for token in tokens {
37        let signed = token.raw() as i16;
38        hasher.update(signed.to_le_bytes());
39    }
40
41    hasher.finalize().into()
42}
43
44/// Perform hash-based matching for a query run.
45///
46/// Computes the hash of the query token sequence and looks for exact matches
47/// in the index. If found, returns a single LicenseMatch with 100% coverage.
48///
49/// # Arguments
50/// * `index` - The license index
51/// * `query_run` - The query run to match
52///
53/// # Returns
54/// Vector of matches (0 or 1 match)
55///
56/// Corresponds to Python: `hash_match()` (lines 59-87)
57pub fn hash_match(index: &LicenseIndex, query_run: &QueryRun) -> Vec<LicenseMatch> {
58    let mut matches = Vec::new();
59    let query_hash = compute_hash(query_run.tokens());
60
61    if let Some(&rid) = index.rid_by_hash.get(&query_hash) {
62        let rule = &index.rules_by_rid[rid];
63        let itokens = &index.tids_by_rid[rid];
64
65        let rule_length = rule.tokens.len();
66
67        let matched_length = query_run.tokens().len();
68        let match_coverage = 100.0;
69
70        let start_line = query_run
71            .line_for_pos(query_run.start)
72            .and_then(LineNumber::new)
73            .unwrap_or(LineNumber::ONE);
74        let end_line = if let Some(end) = query_run.end {
75            query_run
76                .line_for_pos(end)
77                .and_then(LineNumber::new)
78                .unwrap_or(start_line)
79        } else {
80            start_line
81        };
82
83        let end = query_run.end.unwrap_or(query_run.start);
84        let qspan = PositionSpan::range(query_run.start, end + 1);
85        let ispan = PositionSpan::range(0, rule_length);
86        let hispan = PositionSpan::from_positions(
87            (0..rule_length)
88                .filter(|&p| index.dictionary.token_kind(itokens[p]) == TokenKind::Legalese),
89        );
90
91        let license_match = LicenseMatch {
92            license_expression: rule.license_expression.clone(),
93            license_expression_spdx: index
94                .rule_metadata_by_identifier
95                .get(&rule.identifier)
96                .and_then(|metadata| metadata.license_expression_spdx.clone()),
97            from_file: None,
98            start_line,
99            end_line,
100            start_token: query_run.start,
101            end_token: query_run.end.map_or(query_run.start, |e| e + 1),
102            matcher: MATCH_HASH,
103            score: MatchScore::MAX,
104            matched_length,
105            rule_length,
106            match_coverage,
107            rule_relevance: rule.relevance,
108            rid,
109            rule_identifier: rule.identifier.clone(),
110            rule_url: rule.rule_url().unwrap_or_default(),
111            matched_text: None,
112            referenced_filenames: rule.referenced_filenames.clone(),
113            rule_kind: rule.kind(),
114            is_from_license: rule.is_from_license,
115            rule_start_token: 0,
116            coordinates: MatchCoordinates::rule_aligned(qspan, ispan, hispan),
117            candidate_resemblance: 0.0,
118            candidate_containment: 0.0,
119        };
120
121        matches.push(license_match);
122    }
123
124    matches
125}
126
127#[cfg(test)]
128#[path = "hash_match_test.rs"]
129mod tests;
provenant/license_detection/hash_match.rs

provenant/license_detection/
hash_match.rs
