putstate#

Restore a Digest::SHA object’s state from a packed binary string.

The inverse of _getstate. Validates the length of the supplied blob against the receiver’s algorithm and rewrites the internal hash state in place. After a successful _putstate, feeding more data with add continues the hash as if no break had occurred.

The receiver’s algorithm is not changed by this call; it must already match the algorithm the blob was produced under.

Synopsis#

$sha->_putstate($blob);

What you get back#

The receiver on success, undef on failure (invalid length or bad object).

Examples#

my $a = Digest::SHA->new(256);
$a->add("first half");
my $blob = $a->_getstate;

my $b = Digest::SHA->new(256);
$b->_putstate($blob) or die "restore failed";
$b->add("second half");
print $b->hexdigest;

## Round-trip through a file:

open my $in, "<", "hash.state" or die $!;
binmode $in;
my $blob = do { local $/; <$in> };
my $sha = Digest::SHA->new(256);
$sha->_putstate($blob);

Edge cases#

  • Blob length must match the receiver’s algorithm (116 vs 212 bytes); a mismatch returns undef.

  • Called on a non-Digest::SHA object, returns undef.

Differences from upstream#

Fully compatible with upstream Digest::SHA 6.04.

See also#

  • _getstate — produces the blob consumed here.

  • putstate — text-based restore that also creates new objects.

  • load — text-based file-loading counterpart.