songHandler should be currentTrackHandler

This completes the previous work on handlers and trying to clarify the roles of the handlers, between the song/track and the streamUrl.
Previously, the songHandler was prioritized over the streamUrl handler, but it was still missing once case where the $track is a playlist and in fact it's not that $song (master track) handler that should be used but the _currentTrack (sub-track) handler. This is the case where a remote/http playlist is an opml list that contains tracks servced by protocol handlers (e.g. Deezer)

DEVELOPERS.txt

@@ -205,33 +205,35 @@ have been skipped). On further open(), the next sub-track is set in _currentTrac
 - currentTrack() is a method that returns the actual current track, i.e. _currentTrack || _track
 
 >>> Handlers in Slim::Player::Song and Slim::Player::SongStreamingController
-- $song->handler (RO) is set at the creation of the song. it depends on track->url at creation but can
-  be if the PH wants to pass-on to another PH (like thin PH do)
+- $song->handler (RO) is set at the creation of the song. it is based on track->url at creation and is 
+  immutable. 
 - $song->_currentTrackHandler (RW) is set when a single track happens to be a playlist, for each item.
-  It allows each individual sub-tracks to have their own PR when it relates to some of their management.
-  It means that it is empty most of the time.
+  It allows each individual sub-tracks to have their own PH when it relates to some of their management.
+  It means that it is empty most of the time but PH can update it when $track is changed after scanning
+  (for example when upgrding from HTTP to HTTPS)
 - $song->currentTrackHandler() is a method that returns (_currentTrackHandler || handler) so it tells 
   what shall be used for all url related to the current (sub) track
 - $songStreamingController->urlHandler is RO and set at the creation of the song streaming controller, 
   based on the streamUrl (in S::P::Song::open)
 - $songStreamingController->streamHandler is RO and set at creation of the song streaming controller. 
   It is the class of the *socket* object created by $song->handler->new.
-- $songStreamingController->songHandler is a method that returns the $song->handler, so the song main 
-  handler, not the sub-track
+- $songStreamingController->currentTrackHandler is a shortcut to $song->currentTrackhandler
 
 >>> Protocol Handlers
 These files contains a base class but whose methods are called in different contexts (the $self)
-1- a $song context means they are called with a $song->currentHandler or $song->handler
-2- a $sock context means they are called with a $socket (or the object) that was created by $song->handler->new
-3- a simple $url context means they are called by $song->currentHandler, $song->Handler or a $songStreamingController->streamHandler
+1- a $song context means they are called with a $song->currentTrackHandler or $song->handler
+2- a $sock context means they are called with a $socket (or the object) that was created by 
+   $song->handler->new
+3- a simple $url context means they are called by $song->currentTrackHandler, $song->Handler or a 
+   $songStreamingController->streamHandler
 
 So it's a bit confusing that methods from the same package can be object-oriented called with totally
 different type of ancestors/context. In fact, some methods can be called in both context is the 
 ancestor of the PH is capable of (e.g. HTTP).
 
 - functions like sysread are only called with a $sock context
 - functions like getMetadataFor can be called with a $song or an $url context
-- functions like requestString cal be called in a $song or $sock context
+- functions like requestString can be called in a $song or $sock context
 
 >>> Example of requestString
 That function is to create the HTTP headers to be sent with the GET to grab the actual audio. It 

Slim/Player/Protocols/HTTP.pm

@@ -262,9 +262,9 @@ sub getFormatForURL {
 	return Slim::Music::Info::typeFromSuffix($url);
 }
 
-sub getSongHandler {
+sub currentTrackHandler {
 	my ($class, $self, $track) = @_;
-	
+
 	# re-evaluate as we might have been upgraded to HTTPS
 	return $class ne __PACKAGE__ ? $class : Slim::Player::ProtocolHandlers->handlerForURL($track->url);
 }

Slim/Player/Song.pm

@@ -255,7 +255,7 @@ sub getNextSong {
 						if ($self->_track() == $track) {
 							# Update of original track, by playlist or redirection
 							$self->_track($newTrack);	
-							$self->init_accessor(handler => $handler->getSongHandler($self, $newTrack)) if $handler->can('getSongHandler');
+							$self->_currentTrackHandler($handler->currentTrackHandler($self, $newTrack)) if $handler->can('currentTrackHandler');
 
 							main::INFOLOG && $log->info("Track updated by scan: $url -> " . $newTrack->url);
 

Slim/Player/SongStreamController.pm

@@ -63,8 +63,8 @@ sub close {
 	}
 }
 
-sub songHandler {
-	return shift->song->handler();
+sub currentTrackHandler {
+	return shift->song->currentTrackHandler();
 }
 
 sub isDirect {

Slim/Player/Squeezebox.pm

@@ -136,7 +136,7 @@ sub play {
 	my $params = shift;
 
 	my $controller = $params->{'controller'};
-	my $handler = $controller->songHandler();
+	my $handler = $controller->currentTrackHandler();
 
 	# Calculate the correct buffer threshold for remote URLs
 	if ( $handler->isRemote() ) {
@@ -537,7 +537,7 @@ sub stream_s {
 	my $url         = $controller->streamUrl();
 	my $track       = $controller->track();
 	my $handler     = $controller->streamUrlHandler();
-	my $songHandler = $controller->songHandler();
+	my $currentTrackHandler = $controller->currentTrackHandler();
 	my $isDirect    = $controller->isDirect();
 	my $master      = $client->master();
 
@@ -565,7 +565,7 @@ sub stream_s {
 		# use getFormatForURL only if the format is not already given
 		# This method is bad because it only looks at the URL suffix and can cause
 		# (for example) Ogg HTTP streams to be played using the mp3 decoder!
-		my $methodHandler = $songHandler->can('getFormatForURL') ? $songHandler : $handler;
+		my $methodHandler = $currentTrackHandler->can('getFormatForURL') ? $currentTrackHandler : $handler;
 		$format = $methodHandler->getFormatForURL($url) if !$format && $methodHandler;
 	}
 
@@ -752,8 +752,8 @@ sub stream_s {
 		$outputThreshold = 1;
 
 		# Handler may override pcmsamplesize (Rhapsody)
-		if ( $songHandler && $songHandler->can('pcmsamplesize') ) {
-			$pcmsamplesize = $songHandler->pcmsamplesize( $client, $params );
+		if ( $currentTrackHandler && $currentTrackHandler->can('pcmsamplesize') ) {
+			$pcmsamplesize = $currentTrackHandler->pcmsamplesize( $client, $params );
 		}
 
 		# XXX: The use of mp3 as default has been known to cause the mp3 decoder to be used for
@@ -774,7 +774,7 @@ sub stream_s {
 
 		main::INFOLOG && logger('player.streaming.direct')->info("SqueezePlay direct stream: $url");
 
-		my $methodHandler = $songHandler->can('requestString') ? $songHandler : $handler;
+		my $methodHandler = $currentTrackHandler->can('requestString') ? $currentTrackHandler : $handler;
 		$request_string = $methodHandler->getRequestString($client, $url, undef, $params->{'seekdata'} || $controller->song->seekdata);
 		$autostart += 2; # will be 2 for direct streaming with no autostart, or 3 for direct with autostart
 
@@ -818,8 +818,8 @@ sub stream_s {
 		}
 		$server_port = $port;
 
-		# prioritize song's protocol handler at even in direct mode it might change requestString
-		my $methodHandler = $songHandler->can('requestString') ? $songHandler : $handler;
+		# prioritize current track's protocol handler at even in direct mode it might change requestString
+		my $methodHandler = $currentTrackHandler->can('requestString') ? $currentTrackHandler : $handler;
 		$request_string = $methodHandler->requestString($client, $url, undef, $params->{'seekdata'} || $controller->song->seekdata);
 		$autostart += 2; # will be 2 for direct streaming with no autostart, or 3 for direct with autostart
 
@@ -939,10 +939,10 @@ sub stream_s {
 		}
 
 		# Bug 10567, allow plugins to override transition setting
-		if ( $songHandler && $songHandler->can('transitionType') ) {
-			my $override = $songHandler->transitionType( $master, $controller->song(), $transitionType );
+		if ( $currentTrackHandler && $currentTrackHandler->can('transitionType') ) {
+			my $override = $currentTrackHandler->transitionType( $master, $controller->song(), $transitionType );
 			if ( defined $override ) {
-				main::INFOLOG && $log->is_info && $log->info("$songHandler changed transition type to $override");
+				main::INFOLOG && $log->is_info && $log->info("$currentTrackHandler changed transition type to $override");
 				$transitionType = $override;
 			}
 		}

Slim/Player/Squeezebox2.pm

@@ -491,7 +491,7 @@ sub directHeaders {
 	return unless $controller && $controller->isDirect();
 
 	my $url = $controller->streamUrl();
-	my $songHandler = $controller->songHandler();
+	my $currentTrackHandler = $controller->currentTrackHandler();
 
 	# We involve the protocol handler in the header parsing process.
 	# The current iteration of the firmware only knows about HTTP
@@ -529,12 +529,12 @@ sub directHeaders {
 
 			$directlog->warn("Invalid response code ($response) from remote stream $url");
 
-			if ($songHandler && $songHandler->can("handleDirectError")) {
+			if ($currentTrackHandler && $currentTrackHandler->can("handleDirectError")) {
 
 				# bug 10407 - make sure ready to stream again
 				$client->readyToStream(1);
 
-				$songHandler->handleDirectError($client, $url, $response, $status_line);
+				$currentTrackHandler->handleDirectError($client, $url, $response, $status_line);
 			}
 			elsif ($track->can('redir') && $track->redir && $track->redir ne $url) {
 
@@ -569,13 +569,13 @@ sub directHeaders {
 				$directlog->info("Processing " . scalar(@headers) . " headers");
 			}
 
-			# prioritize song's protocol handler over streamUrl handler
-			my $methodHandler = $songHandler->can('parseDirectHeaders') ? $songHandler : $handler;
+			# prioritize current track's protocol handler over streamUrl handler
+			my $methodHandler = $currentTrackHandler->can('parseDirectHeaders') ? $currentTrackHandler : $handler;
 
 			main::INFOLOG && $directlog->info("Calling $methodHandler :: parseDirectHeader");
-			# songHandler relates to the current (sub)track while streamUrl handler just use streamUrl
+			# currentTrackHandler relates to the current (sub)track while streamUrl handler just use streamUrl
 			($title, $bitrate, $metaint, $redir, $contentType, $length, $body) =
-				$methodHandler->parseDirectHeaders($client, $methodHandler == $songHandler ? $controller->song()->currentTrack() : $url, @headers);
+				$methodHandler->parseDirectHeaders($client, $methodHandler == $currentTrackHandler ? $controller->song()->currentTrack() : $url, @headers);
 
 			$controller->song()->isLive($length ? 0 : 1) if !$redir;
 			# XXX maybe should (also) check $song->scanData()->{$url}->{metadata}->{info}->{broadcast}