fix: add AUTOLOAD DESTROY guard, document digest_file_ctx

lib/Digest.pm

@@ -64,6 +64,8 @@ sub AUTOLOAD {
     $class->new( $algorithm, @_ );
 }
 
+sub DESTROY { }    # prevent AUTOLOAD from catching implicit DESTROY calls
+
 1;
 
 __END__

lib/Digest/file.pm

@@ -3,12 +3,11 @@ package Digest::file;
 use strict;
 use warnings;
 
-use Exporter ();
+use base 'Exporter';
 use Carp qw(croak);
 use Digest ();
 
 our $VERSION   = "1.20";
-our @ISA       = qw(Exporter);
 our @EXPORT_OK = qw(digest_file_ctx digest_file digest_file_hex digest_file_base64);
 
 sub digest_file_ctx {
@@ -52,11 +51,24 @@ Digest::file - Calculate digests of files
 
 =head1 DESCRIPTION
 
-This module provide 3 convenience functions to calculate the digest
+This module provide 4 convenience functions to calculate the digest
 of files.  The following functions are provided:
 
 =over
 
+=item digest_file_ctx( $file, $algorithm, [$arg,...] )
+
+This function will open the given file in binary mode, feed its
+contents to a new digest object, and return the L<Digest> context
+object.  This is useful when you need to call a specific digest
+method yourself rather than using one of the shorthand functions
+below.  The function will croak if no algorithm is specified or if
+it fails to open or read the file.
+
+The $algorithm is a string like "MD2", "MD5", "SHA-1", "SHA-512".
+Additional arguments are passed to the constructor for the
+implementation of the given algorithm.
+
 =item digest_file( $file, $algorithm, [$arg,...] )
 
 This function will calculate and return the binary digest of the bytes

t/digest.t

@@ -3,7 +3,7 @@
 use strict;
 use warnings;
 
-use Test::More tests => 4;
+use Test::More tests => 5;
 
 # To find Digest::Dummy
 use lib 't/lib';
@@ -22,3 +22,6 @@ is $d->digest, "ooo";
 $Digest::MMAP{"Dummy-24"} = [ ["NotThere"], "NotThereEither", [ "Digest::Dummy", 24 ] ];
 $d = Digest->new("Dummy-24");
 is $d->digest, "24";
+
+# DESTROY should not trigger AUTOLOAD
+ok( Digest->can("DESTROY"), "Digest has explicit DESTROY method" );

t/file.t

@@ -3,7 +3,7 @@
 use strict;
 use warnings;
 
-use Test::More tests => 5;
+use Test::More tests => 9;
 
 use File::Temp 'tempfile';
 
@@ -32,7 +32,7 @@ use File::Temp 'tempfile';
     }
 }
 
-use Digest::file qw(digest_file digest_file_hex digest_file_base64);
+use Digest::file qw(digest_file_ctx digest_file digest_file_hex digest_file_base64);
 
 {
     my ( $fh, $file ) = tempfile( UNLINK => 1 );
@@ -52,5 +52,21 @@ use Digest::file qw(digest_file digest_file_hex digest_file_base64);
     }
 }
 
+# digest_file_ctx returns a usable Digest context object
+{
+    my ( $fh2, $file2 ) = tempfile( UNLINK => 1 );
+    binmode($fh2);
+    print $fh2 "test data";
+    close($fh2) || die "Can't write '$file2': $!";
+
+    my $ctx = digest_file_ctx( $file2, "Foo" );
+    isa_ok( $ctx, "Digest::Foo", "digest_file_ctx returns correct class" );
+    is( $ctx->digest, "0009", "digest_file_ctx feeds file content to context" );
+}
+
+# Error handling
+ok !eval { digest_file_ctx( "not-there.txt", "Foo" ) };
+like $@, qr/Can't open/, "digest_file_ctx croaks on missing file";
+
 ok !eval { digest_file( "not-there.txt", "Foo" ) };
 ok $@;