icydb_core/db/codec/
cursor.rs

1//! Module: codec::cursor
2//! Responsibility: cursor token formatting codec helpers.
3//! Does not own: cursor validation or planner/runtime continuation semantics.
4//! Boundary: pure wire formatting and bounded decode for cursor token strings.
5
6use crate::db::codec::hex::encode_hex_lower;
7
8// Defensive decode bound for untrusted cursor token input.
9const MAX_CURSOR_TOKEN_HEX_LEN: usize = 8 * 1024;
10
11///
12/// CursorDecodeError
13///
14
15#[derive(Debug, Eq, thiserror::Error, PartialEq)]
16pub enum CursorDecodeError {
17    #[error("cursor token is empty")]
18    Empty,
19
20    #[error("cursor token exceeds max length: {len} hex chars (max {max})")]
21    TooLong { len: usize, max: usize },
22
23    #[error("cursor token must have an even number of hex characters")]
24    OddLength,
25
26    #[error("invalid hex character at position {position}")]
27    InvalidHex { position: usize },
28}
29
30/// Encode raw cursor bytes as a lowercase hex token.
31#[must_use]
32pub fn encode_cursor(bytes: &[u8]) -> String {
33    encode_hex_lower(bytes)
34}
35
36/// Decode a lowercase/uppercase hex cursor token into raw bytes.
37///
38/// The token may include surrounding whitespace, which is trimmed.
39pub fn decode_cursor(token: &str) -> Result<Vec<u8>, CursorDecodeError> {
40    // Phase 1: normalize input and enforce envelope-level bounds.
41    let token = token.trim();
42
43    if token.is_empty() {
44        return Err(CursorDecodeError::Empty);
45    }
46
47    if token.len() > MAX_CURSOR_TOKEN_HEX_LEN {
48        return Err(CursorDecodeError::TooLong {
49            len: token.len(),
50            max: MAX_CURSOR_TOKEN_HEX_LEN,
51        });
52    }
53
54    if !token.len().is_multiple_of(2) {
55        return Err(CursorDecodeError::OddLength);
56    }
57
58    // Phase 2: decode validated hex pairs into raw cursor bytes.
59    let mut out = Vec::with_capacity(token.len() / 2);
60    let bytes = token.as_bytes();
61
62    for idx in (0..bytes.len()).step_by(2) {
63        let hi = decode_hex_nibble(bytes[idx])
64            .ok_or(CursorDecodeError::InvalidHex { position: idx + 1 })?;
65
66        let lo = decode_hex_nibble(bytes[idx + 1])
67            .ok_or(CursorDecodeError::InvalidHex { position: idx + 2 })?;
68
69        out.push((hi << 4) | lo);
70    }
71
72    Ok(out)
73}
74
75const fn decode_hex_nibble(byte: u8) -> Option<u8> {
76    match byte {
77        b'0'..=b'9' => Some(byte - b'0'),
78        b'a'..=b'f' => Some(byte - b'a' + 10),
79        b'A'..=b'F' => Some(byte - b'A' + 10),
80        _ => None,
81    }
82}
83
84///
85/// TESTS
86///
87
88#[cfg(test)]
89mod tests {
90    use super::{CursorDecodeError, MAX_CURSOR_TOKEN_HEX_LEN, decode_cursor, encode_cursor};
91
92    #[test]
93    fn decode_cursor_rejects_empty_and_whitespace_tokens() {
94        let err = decode_cursor("").expect_err("empty token should be rejected");
95        assert_eq!(err, CursorDecodeError::Empty);
96
97        let err = decode_cursor("   \n\t").expect_err("whitespace token should be rejected");
98        assert_eq!(err, CursorDecodeError::Empty);
99    }
100
101    #[test]
102    fn decode_cursor_rejects_odd_length_tokens() {
103        let err = decode_cursor("abc").expect_err("odd-length token should be rejected");
104        assert_eq!(err, CursorDecodeError::OddLength);
105    }
106
107    #[test]
108    fn decode_cursor_enforces_max_token_length() {
109        let accepted = "aa".repeat(MAX_CURSOR_TOKEN_HEX_LEN / 2);
110        let accepted_bytes = decode_cursor(&accepted).expect("max-sized token should decode");
111        assert_eq!(accepted_bytes.len(), MAX_CURSOR_TOKEN_HEX_LEN / 2);
112
113        let rejected = format!("{accepted}aa");
114        let err = decode_cursor(&rejected).expect_err("oversized token should be rejected");
115        assert_eq!(
116            err,
117            CursorDecodeError::TooLong {
118                len: MAX_CURSOR_TOKEN_HEX_LEN + 2,
119                max: MAX_CURSOR_TOKEN_HEX_LEN
120            }
121        );
122    }
123
124    #[test]
125    fn decode_cursor_rejects_invalid_hex_with_position() {
126        let err = decode_cursor("0x").expect_err("invalid hex nibble should be rejected");
127        assert_eq!(err, CursorDecodeError::InvalidHex { position: 2 });
128    }
129
130    #[test]
131    fn decode_cursor_accepts_mixed_case_and_surrounding_whitespace() {
132        let bytes = decode_cursor("  0aFf10  ").expect("mixed-case hex token should decode");
133        assert_eq!(bytes, vec![0x0a, 0xff, 0x10]);
134    }
135
136    #[test]
137    fn encode_decode_cursor_round_trip_is_stable() {
138        let raw = vec![0x00, 0x01, 0x0a, 0xff];
139        let encoded = encode_cursor(&raw);
140        assert_eq!(encoded, "00010aff");
141
142        let decoded = decode_cursor(&encoded).expect("encoded token should decode");
143        assert_eq!(decoded, raw);
144    }
145}
icydb_core/db/codec/cursor.rs

icydb_core/db/codec/
cursor.rs
