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docs: document invariants behind load-bearing expect()s in get_digest_of #8

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docs: document invariants behind load-bearing expect()s in get_digest_of #8

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26 changes: 13 additions & 13 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -211,14 +211,13 @@ where
D: digest::Digest + digest::FixedOutput,
{
pub fn get_digest_of(&self, root_path: &Path) -> Result<Vec<u8>, DigestError> {
// Stack of one hasher per open directory from root to the current entry.
let mut hashers = vec![];

// pop the top hasher and output it to the one just above it
// pop the top hasher and fold it into the one above
fn flush_up_one_level<D: digest::Digest + digest::FixedOutput>(hashers: &mut Vec<D>) {
let hasher = hashers.pop().expect("must not be empty yet");
let h2 = hashers
.last_mut()
.expect("must not happen");
let hasher = hashers.pop().expect("len >= 2 at call site");
let h2 = hashers.last_mut().expect("len >= 2 at call site");
<D as digest::Digest>::update(h2, hasher.finalize_fixed().as_slice());
}

Expand Down Expand Up @@ -263,10 +262,10 @@ where
// names and additional data go the hasher above the one we just prepared
if 0 < depth {
let mut name_hasher = D::new();
// name
// name — non-root entries always have a file_name
hash_osstr(
&mut name_hasher,
entry.path().file_name().expect("must have a file_name"),
entry.path().file_name().expect("non-root entry"),
)?;
// additional data (optional) — folded into the entry-name hash
// per the README algorithm: H(entry_name || 0 || additional_data)
Expand All @@ -277,26 +276,26 @@ where
used: false,
},
)?;
let parent_hasher = hashers.get_mut(depth - 1).expect("must not happen");
let parent_hasher = hashers.get_mut(depth - 1).expect("parent exists for depth > 0");
<D as digest::Digest>::update(
parent_hasher,
name_hasher.finalize_fixed().as_slice(),
);
}

// content
// content — hasher for this entry was just pushed above
if file_type.is_file() {
self.read_content_of_file(
entry.path(),
hashers.last_mut().expect("must not happen"),
hashers.last_mut().expect("just pushed"),
)?;
} else if file_type.is_symlink() {
self.read_content_of_symlink(
entry.path(),
hashers.last_mut().expect("must not happen"),
hashers.last_mut().expect("just pushed"),
)?;
} else if file_type.is_dir() {
let hasher = hashers.last_mut().expect("must not happen");
let hasher = hashers.last_mut().expect("just pushed");
<D as digest::Digest>::update(hasher, b"D");
} else {
return Err(DigestError::FileNotSupported(
Expand All @@ -305,11 +304,12 @@ where
}
}

// Drain nested hashers upward until only the root remains.
loop {
if hashers.len() == 1 {
return Ok(hashers
.pop()
.expect("must not fail")
.expect("len == 1")
.finalize_fixed()
.to_vec());
}
Expand Down