update and changelog

Author: tac0turtle

types/hashing.go

@@ -57,6 +57,10 @@ func (h *Header) Hash() Hash {
 // MemoizeHash computes the header hash and stores it on the header for future
 // Hash() calls. Call this before publishing the header to shared goroutines or
 // caches.
+//
+// If a Header struct is reused (e.g. overwritten via FromProto or field
+// assignment), call InvalidateHash() first to clear the cached value before
+// calling MemoizeHash again. Failure to do so will return the stale cached hash.
 func (h *Header) MemoizeHash() Hash {
 	if h == nil {
 		return nil
@@ -73,6 +77,8 @@ func (h *Header) MemoizeHash() Hash {
 }
 
 func (h *Header) computeHash() Hash {
+	// Legacy hash takes precedence when legacy fields are present (backwards
+	// compatibility). Slim hash is the canonical hash for all other headers.
 	if h.Legacy != nil && !h.Legacy.IsZero() {
 		if legacyHash, err := h.HashLegacy(); err == nil {
 			return legacyHash

types/header.go

@@ -23,6 +23,10 @@ func HeaderFromContext(ctx context.Context) (Header, bool) {
 		return Header{}, false
 	}
 
+	// Clear the memoized hash on the returned copy. The caller may mutate
+	// fields and call Hash() without knowing to call InvalidateHash() first,
+	// which would return a stale cached value.
+	h.InvalidateHash()
 	return h, true
 }