decoder: return const decoder_plugin structs

The decoder_plugin structs must never change.  Don't work with
non-const pointers.

src/decoder_internal.h

@@ -23,7 +23,7 @@
 #include "pcm_utils.h"
 
 struct decoder {
-	struct decoder_plugin *plugin;
+	const struct decoder_plugin *plugin;
 
 	struct pcm_convert_state conv_state;
 

src/decoder_list.c

@@ -65,12 +65,12 @@ static int stringFoundInStringArray(const char *const*array, const char *suffix)
 	return 0;
 }
 
-struct decoder_plugin *decoder_plugin_from_suffix(const char *suffix,
-						  unsigned int next)
+const struct decoder_plugin *
+decoder_plugin_from_suffix(const char *suffix, unsigned int next)
 {
 	static ListNode *pos;
 	ListNode *node;
-	struct decoder_plugin *plugin;
+	const struct decoder_plugin *plugin;
 
 	if (suffix == NULL)
 		return NULL;
@@ -95,8 +95,8 @@ struct decoder_plugin *decoder_plugin_from_suffix(const char *suffix,
 	return NULL;
 }
 
-struct decoder_plugin *decoder_plugin_from_mime_type(const char *mimeType,
-						     unsigned int next)
+const struct decoder_plugin *
+decoder_plugin_from_mime_type(const char *mimeType, unsigned int next)
 {
 	static ListNode *pos;
 	ListNode *node;
@@ -119,13 +119,14 @@ struct decoder_plugin *decoder_plugin_from_mime_type(const char *mimeType,
 	return NULL;
 }
 
-struct decoder_plugin *decoder_plugin_from_name(const char *name)
+const struct decoder_plugin *
+decoder_plugin_from_name(const char *name)
 {
 	void *plugin = NULL;
 
 	findInList(inputPlugin_list, name, &plugin);
 
-	return (struct decoder_plugin *) plugin;
+	return (const struct decoder_plugin *) plugin;
 }
 
 void decoder_plugin_print_all_suffixes(FILE * fp)

src/decoder_list.h

@@ -24,18 +24,19 @@
 struct decoder_plugin;
 
 /* individual functions to load/unload plugins */
-void decoder_plugin_load(struct decoder_plugin * inputPlugin);
-void decoder_plugin_unload(struct decoder_plugin * inputPlugin);
+void decoder_plugin_load(struct decoder_plugin *inputPlugin);
+void decoder_plugin_unload(struct decoder_plugin *inputPlugin);
 
 /* interface for using plugins */
 
-struct decoder_plugin *decoder_plugin_from_suffix(const char *suffix,
-						  unsigned int next);
+const struct decoder_plugin *
+decoder_plugin_from_suffix(const char *suffix, unsigned int next);
 
-struct decoder_plugin *decoder_plugin_from_mime_type(const char *mimeType,
-						     unsigned int next);
+const struct decoder_plugin *
+decoder_plugin_from_mime_type(const char *mimeType, unsigned int next);
 
-struct decoder_plugin *decoder_plugin_from_name(const char *name);
+const struct decoder_plugin *
+decoder_plugin_from_name(const char *name);
 
 void decoder_plugin_print_all_suffixes(FILE * fp);
 

src/decoder_thread.c

@@ -37,7 +37,7 @@ static void decodeStart(void)
 	int ret;
 	bool close_instream = true;
 	struct input_stream inStream;
-	struct decoder_plugin *plugin = NULL;
+	const struct decoder_plugin *plugin;
 
 	if (song_is_file(song))
 		uri = map_song_fs(song, buffer);

src/ls.c

@@ -113,9 +113,10 @@ const char *getSuffix(const char *utf8file)
 	return ret;
 }
 
-struct decoder_plugin *hasMusicSuffix(const char *utf8file, unsigned int next)
+const struct decoder_plugin *
+hasMusicSuffix(const char *utf8file, unsigned int next)
 {
-	struct decoder_plugin *ret = NULL;
+	const struct decoder_plugin *ret = NULL;
 
 	const char *s = getSuffix(utf8file);
 	if (s) {

src/ls.h

@@ -32,7 +32,8 @@ int isValidRemoteUtf8Url(const char *utf8url);
 
 int isRemoteUrl(const char *url);
 
-struct decoder_plugin *hasMusicSuffix(const char *utf8file, unsigned int next);
+const struct decoder_plugin *
+hasMusicSuffix(const char *utf8file, unsigned int next);
 
 int printRemoteUrlHandlers(struct client *client);
 

src/song.c

@@ -96,7 +96,7 @@ song_file_update(struct song *song)
 {
 	char buffer[MPD_PATH_MAX];
 	const char *path_fs;
-	struct decoder_plugin *plugin;
+	const struct decoder_plugin *plugin;
 	unsigned int next = 0;
 	struct stat st;