numos/canonical.py

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"""Canonical serialization and content hashing for numos.state."""

import hashlib


def canonical_body(lines):
    """Join state lines into the exact bytes covered by the C record.

    The C line is excluded so a state file can be hashed before and after
    the hash is stamped into it and get the same answer both times.
    """
    body = [ln for ln in lines if not ln.startswith("C ")]
    return "".join(ln + "\n" for ln in body)


def content_hash(lines):
    """Return the lowercase hex sha256 of the canonical body."""
    return hashlib.sha256(canonical_body(lines).encode("ascii")).hexdigest()