command: allow clients to subscribe to specific idle events

The client may provide the names of idle events as arguments to the
"idle" command to inform MPD that it is only interested in these
events.

src/command.c

@@ -39,6 +39,7 @@
 #include "tag_print.h"
 #include "path.h"
 #include "os_compat.h"
+#include "idle.h"
 
 #define COMMAND_STATUS_VOLUME           "volume"
 #define COMMAND_STATUS_STATE            "state"
@@ -1253,8 +1254,28 @@ static enum command_return
 handle_idle(struct client *client,
 	    mpd_unused int argc, mpd_unused char *argv[])
 {
+        unsigned flags = 0, j;
+        int i;
+        const char *const* idle_names;
+
+        idle_names = idle_get_names();
+        for (i = 1; i < argc; ++i) {
+                if (!argv[i])
+                        continue;
+
+                for (j = 0; idle_names[j]; ++j) {
+                        if (!strcasecmp(argv[i], idle_names[j])) {
+                                flags |= (1 << j);
+                        }
+                }
+        }
+
+        /* No argument means that the client wants to receive everything */
+        if (flags == 0)
+                flags = ~0;
+
 	/* enable "idle" mode on this client */
-	client_idle_wait(client);
+	client_idle_wait(client, flags);
 
 	/* return value is "1" so the caller won't print "OK" */
 	return 1;
@@ -1280,7 +1301,7 @@ static const struct command commands[] = {
 	{ "disableoutput", PERMISSION_ADMIN, 1, 1, handle_disableoutput },
 	{ "enableoutput", PERMISSION_ADMIN, 1, 1, handle_enableoutput },
 	{ "find", PERMISSION_READ, 2, -1, handle_find },
-	{ "idle", PERMISSION_READ, 0, 0, handle_idle },
+	{ "idle", PERMISSION_READ, 0, -1, handle_idle },
 	{ "kill", PERMISSION_ADMIN, -1, -1, handle_kill },
 	{ "list", PERMISSION_READ, 1, -1, handle_list },
 	{ "listall", PERMISSION_READ, 0, 1, handle_listall },