astrid-runtime/astrid · critical

equal chunk identities named different bytes in delta eviden

Error message

equal chunk identities named different bytes in delta evidence

What it means

When measuring delta size between a base and target version, `delta_size` assumes chunk identity (ObjectId) implies identical canonical bytes — content addressing should guarantee this. If a target chunk shares its ID with a base chunk but `canonical_bytes()` differ, the content-addressing invariant is broken and emitting a Copy operation would silently produce wrong data, so the function bails.

Source

Thrown at crates/astrid-storage-chunker-evidence/src/sketch.rs:593

            (None, None) => break,
        }
        sampled = sampled.saturating_add(1);
    }
    (shared, sampled)
}

fn delta_size(base: &Version, target: &Version) -> Result<u64> {
    let mut by_id = BTreeMap::new();
    for chunk in &base.chunks {
        by_id.entry(chunk.id).or_insert(*chunk);
    }
    let mut operations = Vec::new();
    for target_chunk in &target.chunks {
        if let Some(base_chunk) = by_id.get(&target_chunk.id) {
            if base.record(base_chunk.id)?.canonical_bytes()
                != target.record(target_chunk.id)?.canonical_bytes()
            {
                bail!("equal chunk identities named different bytes in delta evidence");
            }
            push_copy(&mut operations, base_chunk.offset, base_chunk.length)?;
        } else {
            push_add(
                &mut operations,
                target.record(target_chunk.id)?.canonical_bytes(),
            )?;
        }
    }
    let encoded = encode_delta(base.file, target.file, target.logical_bytes, &operations)?;
    let reconstructed = apply_delta(&base.materialize()?, &encoded)?;
    if reconstructed != target.materialize()? {
        bail!("encoded evidence delta did not reconstruct its target");
    }
    Ok(u64::try_from(encoded.len())?)
}

fn push_copy(operations: &mut Vec<DeltaOperation>, offset: u64, length: u64) -> Result<()> {

View on GitHub (pinned to affd8760f4)

Solutions

1. Verify object IDs are true content hashes (recompute the hash of canonical_bytes for the mismatched chunk and re-key the record).
2. Rebuild the evidence store / re-chunk the affected files so each chunk ID maps to exactly one byte sequence.
3. Check that base and target records were loaded from the same store with the same serialization configuration.
4. If intentional dedup-by-ID must be relaxed, compare bytes before emitting Copy and emit Add for mismatches instead of bailing.

fn verify_chunk_identity(record: &ObjectRecord, id: ObjectId) -> Result<()> {
    let bytes = record.canonical_bytes();
    let recomputed = hash_content(bytes);
    if recomputed != id {
        bail!("chunk id {id:?} does not hash its content ({recomputed:?})");
    }
    Ok(())
}

fn chunk_ids_match_bytes(base: &ObjectRecord, target: &ObjectRecord) -> bool {
    base.canonical_bytes() == target.canonical_bytes()
}

match delta_size(&base, &target) {
    Err(e) if e.to_string().contains("named different bytes") => {
        eprintln!("content-addressing violated: re-hash and re-key the store");
    },
    r => r?,
}

When it happens

Trigger: Calling `measure_target`/`delta_size` where a target file contains a chunk whose ObjectId exists in the base version's chunk map, but the two records' canonical_bytes() differ — caused by hash collisions, mis-keyed records, or a store where object IDs were reused for different content.

Common situations: Corrupted or hand-assembled object stores; hashing configuration changes (same ID scheme, different byte serialization); evidence stores merged from differently-configured writers.

Understand the failure class

Background: Checksum mismatch errors: "checksum verification failed", "digest mismatch", "expected vs actual checksum" — what they mean and how to fix them — this error's family across 41 libraries.

Related errors

• unexpected {kind:?} in a canonical File owning closure
• durable capsule {id} WASM hash differs between metadata and
• signed Distro.toml does not match Distro.lock manifest_hash;
• encoded evidence delta did not reconstruct its target
• durable capsule {id} disappeared after publish

AI-assisted analysis of astrid-runtime/astrid@affd8760f4 (2026-09-09). Data as JSON: /api/errors/3f98651cd92eba64. Report an issue: GitHub.