icydb_core/db/cursor/
string.rs

1//! Module: cursor::string
2//! Responsibility: external continuation cursor token string formatting.
3//! Does not own: binary token wire encoding or continuation validation semantics.
4//! Boundary: cursor-owned binary token bytes -> lowercase hex external token text.
5
6#[cfg(test)]
7use crate::db::cursor::{GroupedContinuationToken, TokenWireError};
8use crate::db::{codec::hex::encode_hex_lower, cursor::token::MAX_CURSOR_TOKEN_BYTES};
9
10// External cursor tokens are lowercase hex over binary cursor token bytes, so
11// the string limit must allow the full binary token budget after hex expansion.
12const MAX_CURSOR_TOKEN_HEX_LEN: usize = MAX_CURSOR_TOKEN_BYTES * 2;
13
14///
15/// CursorDecodeError
16///
17/// External continuation cursor string decode failures.
18///
19
20#[derive(Debug, Eq, PartialEq)]
21pub enum CursorDecodeError {
22    Empty,
23
24    TooLong { len: usize, max: usize },
25
26    OddLength,
27
28    InvalidHex { position: usize },
29}
30
31/// Encode raw cursor bytes as a lowercase hex token.
32#[must_use]
33pub fn encode_cursor(bytes: &[u8]) -> String {
34    encode_hex_lower(bytes)
35}
36
37/// Encode one grouped continuation token as an external cursor token string.
38#[cfg(test)]
39pub(in crate::db) fn encode_grouped_cursor_token(
40    token: &GroupedContinuationToken,
41) -> Result<String, TokenWireError> {
42    token
43        .encode()
44        .map(|encoded| encode_cursor(encoded.as_slice()))
45}
46
47/// Decode a lowercase/uppercase hex cursor token into raw bytes.
48///
49/// The token may include surrounding whitespace, which is trimmed.
50pub fn decode_cursor(token: &str) -> Result<Vec<u8>, CursorDecodeError> {
51    // Phase 1: normalize input and enforce envelope-level bounds.
52    let token = token.trim();
53
54    if token.is_empty() {
55        return Err(CursorDecodeError::Empty);
56    }
57
58    if token.len() > MAX_CURSOR_TOKEN_HEX_LEN {
59        return Err(CursorDecodeError::TooLong {
60            len: token.len(),
61            max: MAX_CURSOR_TOKEN_HEX_LEN,
62        });
63    }
64
65    if !token.len().is_multiple_of(2) {
66        return Err(CursorDecodeError::OddLength);
67    }
68
69    // Phase 2: decode validated hex pairs into raw cursor bytes.
70    let mut out = Vec::with_capacity(token.len() / 2);
71    let bytes = token.as_bytes();
72
73    for idx in (0..bytes.len()).step_by(2) {
74        let hi = decode_hex_nibble(bytes[idx])
75            .ok_or(CursorDecodeError::InvalidHex { position: idx + 1 })?;
76
77        let lo = decode_hex_nibble(bytes[idx + 1])
78            .ok_or(CursorDecodeError::InvalidHex { position: idx + 2 })?;
79
80        out.push((hi << 4) | lo);
81    }
82
83    Ok(out)
84}
85
86const fn decode_hex_nibble(byte: u8) -> Option<u8> {
87    match byte {
88        b'0'..=b'9' => Some(byte - b'0'),
89        b'a'..=b'f' => Some(byte - b'a' + 10),
90        b'A'..=b'F' => Some(byte - b'A' + 10),
91        _ => None,
92    }
93}
94
95///
96/// TESTS
97///
98
99#[cfg(test)]
100mod tests {
101    use crate::db::cursor::string::{
102        CursorDecodeError, MAX_CURSOR_TOKEN_HEX_LEN, decode_cursor, encode_cursor,
103    };
104
105    #[test]
106    fn decode_cursor_rejects_empty_and_whitespace_tokens() {
107        let err = decode_cursor("").expect_err("empty token should be rejected");
108        assert_eq!(err, CursorDecodeError::Empty);
109
110        let err = decode_cursor("   \n\t").expect_err("whitespace token should be rejected");
111        assert_eq!(err, CursorDecodeError::Empty);
112    }
113
114    #[test]
115    fn decode_cursor_rejects_odd_length_tokens() {
116        let err = decode_cursor("abc").expect_err("odd-length token should be rejected");
117        assert_eq!(err, CursorDecodeError::OddLength);
118    }
119
120    #[test]
121    fn decode_cursor_enforces_max_token_length() {
122        let accepted = "aa".repeat(MAX_CURSOR_TOKEN_HEX_LEN / 2);
123        let accepted_bytes = decode_cursor(&accepted).expect("max-sized token should decode");
124        assert_eq!(accepted_bytes.len(), MAX_CURSOR_TOKEN_HEX_LEN / 2);
125
126        let rejected = format!("{accepted}aa");
127        let err = decode_cursor(&rejected).expect_err("oversized token should be rejected");
128        assert_eq!(
129            err,
130            CursorDecodeError::TooLong {
131                len: MAX_CURSOR_TOKEN_HEX_LEN + 2,
132                max: MAX_CURSOR_TOKEN_HEX_LEN
133            }
134        );
135    }
136
137    #[test]
138    fn decode_cursor_rejects_invalid_hex_with_position() {
139        let err = decode_cursor("0x").expect_err("invalid hex nibble should be rejected");
140        assert_eq!(err, CursorDecodeError::InvalidHex { position: 2 });
141    }
142
143    #[test]
144    fn decode_cursor_accepts_mixed_case_and_surrounding_whitespace() {
145        let bytes = decode_cursor("  0aFf10  ").expect("mixed-case hex token should decode");
146        assert_eq!(bytes, vec![0x0a, 0xff, 0x10]);
147    }
148
149    #[test]
150    fn encode_decode_cursor_round_trip_is_stable() {
151        let raw = vec![0x00, 0x01, 0x0a, 0xff];
152        let encoded = encode_cursor(&raw);
153        assert_eq!(encoded, "00010aff");
154
155        let decoded = decode_cursor(&encoded).expect("encoded token should decode");
156        assert_eq!(decoded, raw);
157    }
158}
icydb_core/db/cursor/string.rs

icydb_core/db/cursor/
string.rs
