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Encapsulate ssz vec decoding in public fn

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This commit is contained in:
Paul Hauner 2019-05-10 16:37:00 +10:00
parent 3ef46c03d1
commit 3cd112d42d
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GPG Key ID: D362883A9218FCC6
3 changed files with 56 additions and 45 deletions
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2
eth2/utils/ssz/src/decode.rs
View File

@ -1,6 +1,6 @@
use super::*;
mod impls;
pub mod impls;
#[derive(Debug, PartialEq)]
pub enum DecodeError {

95
eth2/utils/ssz/src/decode/impls.rs
View File

@ -129,53 +129,62 @@ impl<T: Decodable> Decodable for Vec<T> {
.map(|chunk| T::from_ssz_bytes(chunk))
.collect()
} else {
let mut next_variable_byte = read_offset(bytes)?;
// The value of the first offset must not point back into the same bytes that defined
// it.
if next_variable_byte < BYTES_PER_LENGTH_OFFSET {
return Err(DecodeError::OutOfBoundsByte {
i: next_variable_byte,
});
}
let num_items = next_variable_byte / BYTES_PER_LENGTH_OFFSET;
// The fixed-length section must be a clean multiple of `BYTES_PER_LENGTH_OFFSET`.
if next_variable_byte != num_items * BYTES_PER_LENGTH_OFFSET {
return Err(DecodeError::InvalidByteLength {
len: next_variable_byte,
expected: num_items * BYTES_PER_LENGTH_OFFSET,
});
}
let mut values = Vec::with_capacity(num_items);
for i in 1..=num_items {
let slice_option = if i == num_items {
bytes.get(next_variable_byte..)
} else {
let offset = read_offset(&bytes[(i * BYTES_PER_LENGTH_OFFSET)..])?;
let start = next_variable_byte;
next_variable_byte = offset;
// Note: the condition where `start > next_variable_byte` returns `None` which
// raises an error later in the program.
bytes.get(start..next_variable_byte)
};
let slice = slice_option.ok_or_else(|| DecodeError::OutOfBoundsByte {
i: next_variable_byte,
})?;
values.push(T::from_ssz_bytes(slice)?);
}
Ok(values)
decode_list_of_variable_length_items(bytes)
}
}
}
/// Decodes `bytes` as if it were a list of variable-length items.
///
/// The `ssz::SszDecoder` can also perform this functionality, however it it significantly faster
/// as it is optimized to read same-typed items whilst `ssz::SszDecoder` supports reading items of
/// differing types.
pub fn decode_list_of_variable_length_items<T: Decodable>(
bytes: &[u8],
) -> Result<Vec<T>, DecodeError> {
let mut next_variable_byte = read_offset(bytes)?;
// The value of the first offset must not point back into the same bytes that defined
// it.
if next_variable_byte < BYTES_PER_LENGTH_OFFSET {
return Err(DecodeError::OutOfBoundsByte {
i: next_variable_byte,
});
}
let num_items = next_variable_byte / BYTES_PER_LENGTH_OFFSET;
// The fixed-length section must be a clean multiple of `BYTES_PER_LENGTH_OFFSET`.
if next_variable_byte != num_items * BYTES_PER_LENGTH_OFFSET {
return Err(DecodeError::InvalidByteLength {
len: next_variable_byte,
expected: num_items * BYTES_PER_LENGTH_OFFSET,
});
}
let mut values = Vec::with_capacity(num_items);
for i in 1..=num_items {
let slice_option = if i == num_items {
bytes.get(next_variable_byte..)
} else {
let offset = read_offset(&bytes[(i * BYTES_PER_LENGTH_OFFSET)..])?;
let start = next_variable_byte;
next_variable_byte = offset;
bytes.get(start..next_variable_byte)
};
let slice = slice_option.ok_or_else(|| DecodeError::OutOfBoundsByte {
i: next_variable_byte,
})?;
values.push(T::from_ssz_bytes(slice)?);
}
Ok(values)
}
#[cfg(test)]
mod tests {
use super::*;

4
eth2/utils/ssz/src/lib.rs
View File

@ -1,7 +1,9 @@
mod decode;
mod encode;
pub use decode::{Decodable, DecodeError, SszDecoderBuilder};
pub use decode::{
impls::decode_list_of_variable_length_items, Decodable, DecodeError, SszDecoderBuilder,
};
pub use encode::{Encodable, SszEncoder};
pub const BYTES_PER_LENGTH_OFFSET: usize = 4;