cosmwasm_std/
sections.rs

1use crate::conversion::force_to_u32;
2use crate::prelude::*;
3
4/// A sections decoder for the special case of two elements
5#[allow(dead_code)] // used in Wasm and tests only
6pub fn decode_sections2(data: Vec<u8>) -> (Vec<u8>, Vec<u8>) {
7    let (rest, second) = split_tail(data);
8    let (_, first) = split_tail(rest);
9    (first, second)
10}
11
12/// Encodes multiple sections of data into one vector.
13///
14/// Each section is suffixed by a section length encoded as big endian uint32.
15/// Using suffixes instead of prefixes allows reading sections in reverse order,
16/// such that the first element does not need to be re-allocated if the contract's
17/// data structure supports truncation (such as a Rust vector).
18///
19/// The resulting data looks like this:
20///
21/// ```ignore
22/// section1 || section1_len || section2 || section2_len || section3 || section3_len || …
23/// ```
24#[allow(dead_code)] // used in Wasm and tests only
25pub fn encode_sections(sections: &[&[u8]]) -> Vec<u8> {
26    let mut out_len: usize = sections.iter().map(|section| section.len()).sum();
27    out_len += 4 * sections.len();
28    let mut out_data = Vec::with_capacity(out_len);
29    for &section in sections {
30        let section_len = force_to_u32(section.len()).to_be_bytes();
31        out_data.extend(section);
32        out_data.extend_from_slice(&section_len);
33    }
34    debug_assert_eq!(out_data.len(), out_len);
35    debug_assert_eq!(out_data.capacity(), out_len);
36    out_data
37}
38
39/// Splits data into the last section ("tail") and the rest.
40/// The tail's length information is cut off, such that it is ready to use.
41/// The rest is basically unparsed and contains the lengths of the remaining sections.
42///
43/// While the tail is copied into a new vector, the rest is only truncated such that
44/// no re-allocation is necessary.
45///
46/// If `data` contains one section only, `data` is moved into the tail entirely
47fn split_tail(data: Vec<u8>) -> (Vec<u8>, Vec<u8>) {
48    let tail_len: usize = if data.len() >= 4 {
49        u32::from_be_bytes([
50            data[data.len() - 4],
51            data[data.len() - 3],
52            data[data.len() - 2],
53            data[data.len() - 1],
54        ]) as usize
55    } else {
56        panic!("Cannot read section length");
57    };
58    let rest_len_end = data.len() - 4 - tail_len;
59
60    let (rest, mut tail) = if rest_len_end == 0 {
61        // i.e. all data is the tail
62        (Vec::new(), data)
63    } else {
64        let mut rest = data;
65        let tail = rest.split_off(rest_len_end);
66        (rest, tail)
67    };
68    tail.truncate(tail_len); // cut off length
69    (rest, tail)
70}
71
72#[cfg(test)]
73mod tests {
74    use super::*;
75
76    #[test]
77    fn decode_sections2_works() {
78        let data = b"\xAA\0\0\0\x01\xBB\xCC\0\0\0\x02".to_vec();
79        assert_eq!(decode_sections2(data), (vec![0xAA], vec![0xBB, 0xCC]));
80
81        let data = b"\xDE\xEF\x62\0\0\0\x03\0\0\0\0".to_vec();
82        assert_eq!(decode_sections2(data), (vec![0xDE, 0xEF, 0x62], vec![]));
83
84        let data = b"\0\0\0\0\xDE\xEF\x62\0\0\0\x03".to_vec();
85        assert_eq!(decode_sections2(data), (vec![], vec![0xDE, 0xEF, 0x62]));
86
87        let data = b"\0\0\0\0\0\0\0\0".to_vec();
88        assert_eq!(decode_sections2(data), (vec![], vec![]));
89
90        let data = b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\0\0\0\x13\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\0\0\x01\x15".to_vec();
91        assert_eq!(decode_sections2(data), (vec![0xFF; 19], vec![0x9D; 277]));
92    }
93
94    #[test]
95    fn decode_sections2_preserved_first_vector() {
96        let original = b"\xAA\0\0\0\x01\xBB\xCC\0\0\0\x02".to_vec();
97        let original_capacity = original.capacity();
98        let original_ptr = original.as_ptr();
99        let (first, second) = decode_sections2(original);
100
101        // This is not copied
102        assert_eq!(first.capacity(), original_capacity);
103        assert_eq!(first.as_ptr(), original_ptr);
104
105        // This is a copy
106        assert_ne!(second.capacity(), original_capacity);
107        assert_ne!(second.as_ptr(), original_ptr);
108    }
109
110    #[test]
111    fn encode_sections_works_for_empty_sections() {
112        let enc = encode_sections(&[]);
113        assert_eq!(enc, b"" as &[u8]);
114        let enc = encode_sections(&[&[]]);
115        assert_eq!(enc, b"\0\0\0\0" as &[u8]);
116        let enc = encode_sections(&[&[], &[]]);
117        assert_eq!(enc, b"\0\0\0\0\0\0\0\0" as &[u8]);
118        let enc = encode_sections(&[&[], &[], &[]]);
119        assert_eq!(enc, b"\0\0\0\0\0\0\0\0\0\0\0\0" as &[u8]);
120    }
121
122    #[test]
123    fn encode_sections_works_for_one_element() {
124        let enc = encode_sections(&[]);
125        assert_eq!(enc, b"" as &[u8]);
126        let enc = encode_sections(&[&[0xAA]]);
127        assert_eq!(enc, b"\xAA\0\0\0\x01" as &[u8]);
128        let enc = encode_sections(&[&[0xAA, 0xBB]]);
129        assert_eq!(enc, b"\xAA\xBB\0\0\0\x02" as &[u8]);
130        let enc = encode_sections(&[&[0x9D; 277]]);
131        assert_eq!(enc, b"\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\x9D\0\0\x01\x15" as &[u8]);
132    }
133
134    #[test]
135    fn encode_sections_works_for_multiple_elements() {
136        let enc = encode_sections(&[&[0xAA]]);
137        assert_eq!(enc, b"\xAA\0\0\0\x01" as &[u8]);
138        let enc = encode_sections(&[&[0xAA], &[0xDE, 0xDE]]);
139        assert_eq!(enc, b"\xAA\0\0\0\x01\xDE\xDE\0\0\0\x02" as &[u8]);
140        let enc = encode_sections(&[&[0xAA], &[0xDE, 0xDE], &[]]);
141        assert_eq!(enc, b"\xAA\0\0\0\x01\xDE\xDE\0\0\0\x02\0\0\0\0" as &[u8]);
142        let enc = encode_sections(&[&[0xAA], &[0xDE, 0xDE], &[], &[0xFF; 19]]);
143        assert_eq!(enc, b"\xAA\0\0\0\x01\xDE\xDE\0\0\0\x02\0\0\0\0\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\0\0\0\x13" as &[u8]);
144    }
145}
cosmwasm_std/sections.rs

cosmwasm_std/
sections.rs
