Deserialize branch

[richardpringle]

Delegate branch deserialization to the branch-module.

[rkuris]

Approved with nits

[rkuris]

nit: This TODO seems relevant still, but it was deleted.

[richardpringle]

Will go away shortly

[rkuris]

nit: this will get a clippy exception due to unhandled panic once we add the clippy rules. Maybe:

Suggested change

	.as_deref()[0] as u64;
	.as_deref().get(0).ok_or(...)? as u64;

[richardpringle]

🤔 this could also be solved with a macro. We should be casting to an array and using from_be_bytes such that we can make the size any valid numeric type. I'll add a comment to #396

[richardpringle]

#396 (comment)

[rkuris]

nit: clearer if this and the prior statement were reversed. Perhaps increase addr before setting and testing len.

[richardpringle]

To go along with your comment about the macro, every time we get a view, we should automatically advance the address. I created #396 to address this

[rkuris]

nit: Is this comment wrong? This assumes that all branch nodes have no data.

[richardpringle]

Will go away shortly

[rkuris]

nit (DRY): identical code could be refactored into a macro, maybe:

macro_rules! read_data {
    ($cursor:expr, $type:ty) => {{
        let mut buf = [0u8; std::mem::size_of::<$type>()];
        $cursor.read_exact(&mut buf)?;
        <$type>::from_le_bytes(buf)
    }};
}

Then, at the callsite, you can do all the manipulation:

            *child = Some(read_data!(cursor, usize))
                .filter(|addr| *addr != 0)
                .map(DiskAddress::from);

[richardpringle]

#396

[xinifinity]

nit: this line can be removed with the TODO above?

[richardpringle]

Will go away shortly