fromJson static method

PatchbayCatalogDigest? fromJson(Object? value)

Reads a digest a host served, or null when there is none to read.

Deliberately hand-written rather than delegating to the generated PatchbayCatalogDigestWire.fromJson: that decoder rejects unknown fields, which is right for a request a host has to police and wrong for a forward-compatibility mechanism. A newer host that attaches something extra here must leave this reader with a digest it can still evaluate, not with a decode failure.

Tolerance stops at the edge of covers. An unknown sibling field is safe to ignore — it does not change what the fields this version does understand mean. An unreadable entry inside covers is the opposite: dropping it silently narrows the host's claim, and a narrowed claim that happens to land on this version's coverage reads as "I understood all of it" when the truth is "I could not read part of it". So an entry that is not a string poisons the whole coverage via coversFullyRead, and the digest degrades to not-recomputable — the same fail-closed answer an unknown algorithm gets, for the same reason.

Implementation

static PatchbayCatalogDigest? fromJson(Object? value) {
  if (value is! Map<Object?, Object?>) return null;
  final Object? algorithm = value['algorithm'];
  final Object? covers = value['covers'];
  final Object? digest = value['value'];
  if (algorithm is! String || digest is! String || covers is! List<Object?>) {
    return null;
  }
  return PatchbayCatalogDigest(
    algorithm: algorithm,
    covers: <String>[
      for (final Object? scope in covers)
        if (scope is String) scope,
    ],
    coversFullyRead: covers.every((Object? scope) => scope is String),
    value: digest,
  );
}