db/proxy: fall back to recursive walk on old libmpdclient/MPD

Error message was 'too few arguments for "find"' because the "base"
constraint was not supported, and no other constraints remained.

NEWS

@@ -1,6 +1,7 @@
 ver 0.18.12 (not yet released)
 * database
   - proxy: fix build failure with libmpdclient 2.2
+  - proxy: fix add/search and other commands with libmpdclient < 2.9
 
 ver 0.18.11 (2014/05/12)
 * decoder

src/DatabaseSelection.cxx

@@ -30,6 +30,18 @@ DatabaseSelection::DatabaseSelection(const char *_uri, bool _recursive,
 		uri = filter->GetBase();
 }
 
+bool
+DatabaseSelection::IsEmpty() const
+{
+	return uri.empty() && (filter == nullptr || filter->IsEmpty());
+}
+
+bool
+DatabaseSelection::HasOtherThanBase() const
+{
+	return filter != nullptr && filter->HasOtherThanBase();
+}
+
 bool
 DatabaseSelection::Match(const Song &song) const
 {

src/DatabaseSelection.hxx

@@ -44,6 +44,15 @@ struct DatabaseSelection {
 	DatabaseSelection(const char *_uri, bool _recursive,
 			  const SongFilter *_filter=nullptr);
 
+	gcc_pure
+	bool IsEmpty() const;
+
+	/**
+	 * Does this selection contain constraints other than "base"?
+	 */
+	gcc_pure
+	bool HasOtherThanBase() const;
+
 	gcc_pure
 	bool Match(const Song &song) const;
 };

src/SongFilter.cxx

@@ -203,6 +203,16 @@ SongFilter::Match(const Song &song) const
 	return true;
 }
 
+bool
+SongFilter::HasOtherThanBase() const
+{
+	for (const auto &i : items)
+		if (i.GetTag() != LOCATE_TAG_BASE_TYPE)
+			return true;
+
+	return false;
+}
+
 std::string
 SongFilter::GetBase() const
 {

src/SongFilter.hxx

@@ -109,6 +109,11 @@ public:
 		return items;
 	}
 
+	gcc_pure
+	bool IsEmpty() const {
+		return items.empty();
+	}
+
 	/**
 	 * Is there at least one item with "fold case" enabled?
 	 */
@@ -121,6 +126,12 @@ public:
 		return false;
 	}
 
+	/**
+	 * Does this filter contain constraints other than "base"?
+	 */
+	gcc_pure
+	bool HasOtherThanBase() const;
+
 	/**
 	 * Returns the "base" specification (if there is one) or an
 	 * empty string.

src/db/ProxyDatabasePlugin.cxx

@@ -566,6 +566,23 @@ SearchSongs(struct mpd_connection *connection,
 	return result && CheckError(connection, error);
 }
 
+/**
+ * Check whether we can use the "base" constraint.  Requires
+ * libmpdclient 2.9 and MPD 0.18.
+ */
+gcc_pure
+static bool
+ServerSupportsSearchBase(const struct mpd_connection *connection)
+{
+#if LIBMPDCLIENT_CHECK_VERSION(2,9,0)
+	return mpd_connection_cmp_server_version(connection, 0, 18, 0) >= 0;
+#else
+	(void)connection;
+
+	return false;
+#endif
+}
+
 bool
 ProxyDatabase::Visit(const DatabaseSelection &selection,
 		     VisitDirectory visit_directory,
@@ -577,7 +594,10 @@ ProxyDatabase::Visit(const DatabaseSelection &selection,
 	if (!const_cast<ProxyDatabase *>(this)->EnsureConnected(error))
 		return nullptr;
 
-	if (!visit_directory && !visit_playlist && selection.recursive)
+	if (!visit_directory && !visit_playlist && selection.recursive &&
+	    (ServerSupportsSearchBase(connection)
+	     ? !selection.IsEmpty()
+	     : selection.HasOtherThanBase()))
 		/* this optimized code path can only be used under
 		   certain conditions */
 		return ::SearchSongs(connection, selection, visit_song, error);