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Add decode_sections()
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‎packages/vm/src/sections.rs

Lines changed: 87 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,22 @@
11
use crate::conversion::to_u32;
22
use crate::errors::VmResult;
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/// Decodes sections of data into multiple slices.
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///
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/// Each encoded section is suffixed by a section length, encoded as big endian uint32.
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///
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/// See also: `encode_section`.
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pub fn decode_sections(data: &[u8]) -> Vec<&[u8]> {
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let mut result: Vec<&[u8]> = vec![];
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let lengths = extract_lengths(data);
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let mut start = 0;
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for length in lengths.iter().rev() {
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result.push(&data[start..start + length]);
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start += length + 4;
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}
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result
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}
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/// Encodes multiple sections of data into one vector.
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///
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/// Each section is suffixed by a section length encoded as big endian uint32.
@@ -28,10 +44,80 @@ pub fn encode_sections(sections: &[Vec<u8>]) -> VmResult<Vec<u8>> {
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Ok(out_data)
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}
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/// Extracts the lengths of encoded vectors.
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///
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/// Starts from the end of `data`, and computes a (reverse) list of lengths.
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fn extract_lengths(data: &[u8]) -> Vec<usize> {
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let mut lengths = vec![];
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let mut remaining_len = data.len();
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while remaining_len >= 4 {
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let tail_len = u32::from_be_bytes([
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data[remaining_len - 4],
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data[remaining_len - 3],
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data[remaining_len - 2],
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data[remaining_len - 1],
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]) as usize;
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lengths.push(tail_len);
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remaining_len -= 4 + tail_len;
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}
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lengths
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}
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3166
#[cfg(test)]
3267
mod tests {
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use super::*;
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#[test]
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fn decode_sections_works_for_empty_sections() {
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let dec = decode_sections(&[]);
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assert_eq!(dec.len(), 0);
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let dec = decode_sections(b"\0\0\0\0");
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assert_eq!(dec, &[&[0u8; 0]]);
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let dec = decode_sections(b"\0\0\0\0\0\0\0\0");
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assert_eq!(dec, &[&[0u8; 0]; 2]);
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let dec = decode_sections(b"\0\0\0\0\0\0\0\0\0\0\0\0");
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assert_eq!(dec, &[&[0u8; 0]; 3]);
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// ignores "trailing" stuff
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let dec = decode_sections(b"\0\0\0\0\0\0\0\0\0\0\0");
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assert_eq!(dec, &[&[0u8; 0]; 2]);
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}
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#[test]
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fn decode_sections_works_for_one_element() {
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let dec = decode_sections(b"\xAA\0\0\0\x01");
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assert_eq!(dec, &[vec![0xAA]]);
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let dec = decode_sections(b"\xAA\xBB\0\0\0\x02");
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assert_eq!(dec, &[vec![0xAA, 0xBB]]);
91+
let dec = decode_sections(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");
92+
assert_eq!(dec, &[vec![0x9D; 277]]);
93+
}
94+
95+
#[test]
96+
fn decode_sections_works_for_two_elements() {
97+
let data = b"\xAA\0\0\0\x01\xBB\xCC\0\0\0\x02".to_vec();
98+
assert_eq!(decode_sections(&data), &[vec![0xAA], vec![0xBB, 0xCC]]);
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let data = b"\xDE\xEF\x62\0\0\0\x03\0\0\0\0".to_vec();
100+
assert_eq!(decode_sections(&data), &[vec![0xDE, 0xEF, 0x62], vec![]]);
101+
let data = b"\0\0\0\0\xDE\xEF\x62\0\0\0\x03".to_vec();
102+
assert_eq!(decode_sections(&data), &[vec![], vec![0xDE, 0xEF, 0x62]]);
103+
let data = b"\0\0\0\0\0\0\0\0".to_vec();
104+
assert_eq!(decode_sections(&data), &[vec![0u8; 0], vec![]]);
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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();
106+
assert_eq!(decode_sections(&data), &[vec![0xFF; 19], vec![0x9D; 277]]);
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}
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#[test]
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fn decode_sections_works_for_multiple_elements() {
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let dec = decode_sections(b"\xAA\0\0\0\x01");
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assert_eq!(dec, &[vec![0xAA]]);
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let dec = decode_sections(b"\xAA\0\0\0\x01\xDE\xDE\0\0\0\x02");
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assert_eq!(dec, &[vec![0xAA], vec![0xDE, 0xDE]]);
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let dec = decode_sections(b"\xAA\0\0\0\x01\xDE\xDE\0\0\0\x02\0\0\0\0");
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assert_eq!(dec, &[vec![0xAA], vec![0xDE, 0xDE], vec![]]);
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let dec = decode_sections(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");
118+
assert_eq!(dec, &[vec![0xAA], vec![0xDE, 0xDE], vec![], vec![0xFF; 19]]);
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}
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35121
#[test]
36122
fn encode_sections_works_for_empty_sections() {
37123
let enc = encode_sections(&[]).unwrap();
@@ -67,4 +153,4 @@ mod tests {
67153
let enc = encode_sections(&[vec![0xAA], vec![0xDE, 0xDE], vec![], vec![0xFF; 19]]).unwrap();
68154
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]);
69155
}
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}
156+
}

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