Added a guarantee that the TrackSerialiser won't modify tracks it receives.

Storage/Disk/Track/PCMPatchedTrack.cpp

@@ -27,7 +27,7 @@ PCMPatchedTrack::PCMPatchedTrack(const PCMPatchedTrack &original) {
 	active_period_ = periods_.begin();
 }
 
-Track *PCMPatchedTrack::clone() {
+Track *PCMPatchedTrack::clone() const {
 	return new PCMPatchedTrack(*this);
 }
 

Storage/Disk/Track/PCMPatchedTrack.hpp

@@ -43,9 +43,9 @@ class PCMPatchedTrack: public Track {
 		void add_segment(const Time &start_time, const PCMSegment &segment, bool clamp_to_index_hole);
 
 		// To satisfy Storage::Disk::Track
-		Event get_next_event();
-		Time seek_to(const Time &time_since_index_hole);
-		Track *clone();
+		Event get_next_event() override;
+		Time seek_to(const Time &time_since_index_hole) override;
+		Track *clone() const override;
 
 	private:
 		std::shared_ptr<Track> underlying_track_;

Storage/Disk/Track/PCMTrack.cpp

@@ -46,7 +46,7 @@ PCMTrack::PCMTrack(const PCMTrack &original) : PCMTrack() {
 	segment_event_sources_ = original.segment_event_sources_;
 }
 
-Track *PCMTrack::clone() {
+Track *PCMTrack::clone() const {
 	return new PCMTrack(*this);
 }
 

Storage/Disk/Track/PCMTrack.hpp

@@ -42,9 +42,9 @@ class PCMTrack: public Track {
 		PCMTrack(const PCMTrack &);
 
 		// as per @c Track
-		Event get_next_event();
-		Time seek_to(const Time &time_since_index_hole);
-		Track *clone();
+		Event get_next_event() override;
+		Time seek_to(const Time &time_since_index_hole) override;
+		Track *clone() const override;
 
 	private:
 		// storage for the segments that describe this track

Storage/Disk/Track/Track.hpp

@@ -114,7 +114,7 @@ class Track {
 		/*!
 			The virtual copy constructor pattern; returns a copy of the Track.
 		*/
-		virtual Track *clone() = 0;
+		virtual Track *clone() const = 0;
 };
 
 }

Storage/Disk/Track/TrackSerialiser.cpp

@@ -8,11 +8,14 @@
 
 #include "TrackSerialiser.hpp"
 
+#include <memory>
+
 // TODO: if this is a PCMTrack with only one segment and that segment's bit rate is within tolerance,
 // just return a copy of that segment.
-Storage::Disk::PCMSegment Storage::Disk::track_serialisation(Track &track, Time length_of_a_bit) {
+Storage::Disk::PCMSegment Storage::Disk::track_serialisation(const Track &track, Time length_of_a_bit) {
 	unsigned int history_size = 16;
 	DigitalPhaseLockedLoop pll(100, history_size);
+	std::unique_ptr<Track> track_copy(track.clone());
 
 	struct ResultAccumulator: public DigitalPhaseLockedLoop::Delegate {
 		PCMSegment result;
@@ -29,12 +32,12 @@ Storage::Disk::PCMSegment Storage::Disk::track_serialisation(Track &track, Time
 	length_multiplier.simplify();
 
 	// start at the index hole
-	track.seek_to(Time(0));
+	track_copy->seek_to(Time(0));
 
 	// grab events until the next index hole
 	Time time_error = Time(0);
 	while(true) {
-		Track::Event next_event = track.get_next_event();
+		Track::Event next_event = track_copy->get_next_event();
 		if(next_event.type == Track::Event::IndexHole) break;
 
 		Time extended_length = next_event.length * length_multiplier + time_error;
@@ -47,7 +50,7 @@ Storage::Disk::PCMSegment Storage::Disk::track_serialisation(Track &track, Time
 		if(history_size) {
 			history_size--;
 			if(!history_size) {
-				track.seek_to(Time(0));
+				track_copy->seek_to(Time(0));
 				time_error.set_zero();
 				pll.set_delegate(&result_accumulator);
 			}

Storage/Disk/Track/TrackSerialiser.hpp

@@ -30,7 +30,7 @@ namespace Disk {
 	@param length_of_a_bit The expected length of a single bit, as a proportion of the
 	track length.
 */
-PCMSegment track_serialisation(Track &track, Time length_of_a_bit);
+PCMSegment track_serialisation(const Track &track, Time length_of_a_bit);
 
 }
 }

Storage/Disk/Track/UnformattedTrack.cpp

@@ -21,6 +21,6 @@ Storage::Time UnformattedTrack::seek_to(const Time &time_since_index_hole) {
 	return Time(0);
 }
 
-Track *UnformattedTrack::clone() {
+Track *UnformattedTrack::clone() const {
 	return new UnformattedTrack;
 }

Storage/Disk/Track/UnformattedTrack.hpp

@@ -19,9 +19,9 @@ namespace Disk {
 */
 class UnformattedTrack: public Track {
 	public:
-		Event get_next_event();
-		Time seek_to(const Time &time_since_index_hole);
-		Track *clone();
+		Event get_next_event() override;
+		Time seek_to(const Time &time_since_index_hole) override;
+		Track *clone() const override;
 };
 
 }