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Introduce Rlp::at_with_offset method. #269

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merged 2 commits into from
Nov 20, 2019
Merged

Introduce Rlp::at_with_offset method. #269

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4f4e81c
Introduce Rlp::at_with_offset.
jimpo Nov 19, 2019
46b7272
Method docs for Rlp::at and Rlp::at_with_offset.
jimpo Nov 20, 2019
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21 changes: 19 additions & 2 deletions rlp/src/rlpin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -186,9 +186,25 @@ impl<'a> Rlp<'a> {
}
}

/// Returns an Rlp item in a list at the given index.
///
/// Returns an error if this Rlp is not a list or if the index is out of range.
pub fn at<'view>(&'view self, index: usize) -> Result<Rlp<'a>, DecoderError>
where
'a: 'view,
{
let (rlp, _offset) = self.at_with_offset(index)?;
Ok(rlp)
}

/// Returns an Rlp item in a list at the given index along with the byte offset into the
/// raw data slice.
///
/// Returns an error if this Rlp is not a list or if the index is out of range.
pub fn at_with_offset<'view>(&'view self, index: usize)
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What is the purpose of adding this as a new method rather than changing the return value of at()? Just to reduce the breakage in parity-ethereum? If yes then I think I'd prefer to do a breaking release of rlp and do the grunt work.

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@jimpo jimpo Nov 20, 2019 •
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Well, most of the time you don't need the offset, so even if designing the API from scratch I think having two separate methods probably makes sense. At the moment this is only used for rlp-encoded trie nodes.

But yeah, probably the main reason is backwards compatibility. Just doesn't seem like there's a good reason to break the current API, IMO.

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most of the time you don't need the offset,

In your eth branch it's used 4 times and only for RlpNodeCodec so I guess you're right. at() is used much more extensively, which kind of surprised me: I'd have hoped it was used much less.

-> Result<(Rlp<'a>, usize), DecoderError>
where
'a: 'view,
{
if !self.is_list() {
return Err(DecoderError::RlpExpectedToBeList);
Expand All @@ -211,11 +227,12 @@ impl<'a> Rlp<'a> {
let (bytes, consumed) = Rlp::consume_items(bytes, indexes_to_skip)?;

// update the cache
self.offset_cache.set(Some(OffsetCache::new(index, bytes_consumed + consumed)));
let offset = bytes_consumed + consumed;
self.offset_cache.set(Some(OffsetCache::new(index, offset)));

// construct new rlp
let found = BasicDecoder::payload_info(bytes)?;
Ok(Rlp::new(&bytes[0..found.header_len + found.value_len]))
Ok((Rlp::new(&bytes[0..found.header_len + found.value_len]), offset))
}

pub fn is_null(&self) -> bool {
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29 changes: 29 additions & 0 deletions rlp/tests/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,35 @@ fn rlp_at() {
}
}

#[test]
fn rlp_at_with_offset() {
let data = vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g'];
{
let rlp = Rlp::new(&data);
assert!(rlp.is_list());
let animals: Vec<String> = rlp.as_list().unwrap();
assert_eq!(animals, vec!["cat".to_owned(), "dog".to_owned()]);

let (cat, cat_offset) = rlp.at_with_offset(0).unwrap();
assert!(cat.is_data());
assert_eq!(cat_offset, 1);
assert_eq!(cat.as_raw(), &[0x83, b'c', b'a', b't']);
assert_eq!(cat.as_val::<String>().unwrap(), "cat".to_owned());

let (dog, dog_offset) = rlp.at_with_offset(1).unwrap();
assert!(dog.is_data());
assert_eq!(dog_offset, 5);
assert_eq!(dog.as_raw(), &[0x83, b'd', b'o', b'g']);
assert_eq!(dog.as_val::<String>().unwrap(), "dog".to_owned());

let (cat_again, cat_offset) = rlp.at_with_offset(0).unwrap();
assert!(cat_again.is_data());
assert_eq!(cat_offset, 1);
assert_eq!(cat_again.as_raw(), &[0x83, b'c', b'a', b't']);
assert_eq!(cat_again.as_val::<String>().unwrap(), "cat".to_owned());
}
}

#[test]
fn rlp_at_err() {
let data = vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o'];
Expand Down