Fix failure to load OV after adding a VF to a project.

This has the same cause as
19f51503621a57794bd79bac053c9e6549a69f46
i.e. the DCPDecoder re-use optimisation.  This commit tries to
re-fix 19f515 in a more general way which also takes into account
the OV/VF bug.  It also adds a unit test.

3 files changed, 37 insertions, 10 deletions

diff --git a/src/lib/dcp_decoder.cc b/src/lib/dcp_decoder.cc
index 95cad9266..4b189189e 100644
--- a/src/lib/dcp_decoder.cc
+++ b/src/lib/dcp_decoder.cc
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2014-2018 Carl Hetherington <cth@carlh.net>
+    Copyright (C) 2014-2019 Carl Hetherington <cth@carlh.net>
 
     This file is part of DCP-o-matic.
 
@@ -28,6 +28,7 @@
 #include "ffmpeg_image_proxy.h"
 #include "image.h"
 #include "config.h"
+#include "digester.h"
 #include <dcp/dcp.h>
 #include <dcp/cpl.h>
 #include <dcp/reel.h>
@@ -52,6 +53,7 @@
 
 using std::list;
 using std::cout;
+using std::string;
 using boost::shared_ptr;
 using boost::dynamic_pointer_cast;
 using boost::optional;
@@ -75,16 +77,18 @@ DCPDecoder::DCPDecoder (shared_ptr<const Film> film, shared_ptr<const DCPContent
 		}
 	}
 
-	if (old) {
-		_reels = old->_reels;
+	/* We try to avoid re-scanning the DCP's files every time we make a new DCPDecoder; we do this
+	   by re-using the _reels list.  Before we do this we need to check that nothing too serious
+	   has changed in the DCPContent.
 
-		/* We might have gained a KDM since we made the Reel objects */
-		if (_dcp_content->kdm ()) {
-			dcp::DecryptedKDM k = decrypted_kdm ();
-			BOOST_FOREACH (shared_ptr<dcp::Reel> i, _reels) {
-				i->add (k);
-			}
-		}
+	   We do this by storing a digest of the important bits of the DCPContent and then checking that's
+	   the same before we re-use _reels.
+	*/
+
+	_lazy_digest = calculate_lazy_digest (c);
+
+	if (old && old->lazy_digest() == _lazy_digest) {
+		_reels = old->_reels;
 	} else {
 
 		list<shared_ptr<dcp::CPL> > cpl_list = cpls ();
@@ -425,3 +429,18 @@ DCPDecoder::set_forced_reduction (optional<int> reduction)
 {
 	_forced_reduction = reduction;
 }
+
+string
+DCPDecoder::calculate_lazy_digest (shared_ptr<const DCPContent> c) const
+{
+	Digester d;
+	BOOST_FOREACH (boost::filesystem::path i, c->paths()) {
+		d.add (i.string());
+	}
+	d.add (static_cast<bool>(_dcp_content->kdm()));
+	d.add (static_cast<bool>(c->cpl()));
+	if (c->cpl()) {
+		d.add (c->cpl().get());
+	}
+	return d.get ();
+}
diff --git a/src/lib/dcp_decoder.h b/src/lib/dcp_decoder.h
index 2e63b24a2..496d95740 100644
--- a/src/lib/dcp_decoder.h
+++ b/src/lib/dcp_decoder.h
@@ -58,6 +58,10 @@ public:
 	bool pass ();
 	void seek (dcpomatic::ContentTime t, bool accurate);
 
+	std::string lazy_digest () const {
+		return _lazy_digest;
+	}
+
 private:
 	friend struct dcp_subtitle_within_dcp_test;
 
@@ -72,6 +76,7 @@ private:
 		boost::shared_ptr<TextDecoder> decoder,
 		dcp::Size size
 		);
+	std::string calculate_lazy_digest (boost::shared_ptr<const DCPContent>) const;
 
 	/** Time of next thing to return from pass relative to the start of _reel */
 	dcpomatic::ContentTime _next;
@@ -89,4 +94,6 @@ private:
 
 	bool _decode_referenced;
 	boost::optional<int> _forced_reduction;
+
+	std::string _lazy_digest;
 };
diff --git a/src/lib/player.h b/src/lib/player.h
index 7558f6da0..e99c345bb 100644
--- a/src/lib/player.h
+++ b/src/lib/player.h
@@ -110,6 +110,7 @@ private:
 	friend struct player_subframe_test;
 	friend struct empty_test1;
 	friend struct empty_test2;
+	friend struct check_reuse_old_data_test;
 
 	void setup_pieces ();
 	void setup_pieces_unlocked ();