db/upnp: add UpnpMakeAction() helper function

Makefile.am

@@ -424,6 +424,7 @@ libdb_plugins_a_SOURCES += \
 	src/db/upnp/ixmlwrap.cxx src/db/upnp/ixmlwrap.hxx \
 	src/db/upnp/upnpplib.cxx src/db/upnp/upnpplib.hxx \
 	src/db/upnp/Util.cxx src/db/upnp/Util.hxx \
+	src/db/upnp/Action.hxx \
 	src/db/upnp/WorkQueue.hxx \
 	src/db/upnp/Object.hxx
 DB_LIBS += \

src/db/upnp/Action.hxx

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_UPNP_ACTION_HXX
+#define MPD_UPNP_ACTION_HXX
+
+#include "Compiler.h"
+
+#include <upnp/upnptools.h>
+
+static inline constexpr unsigned
+CountNameValuePairs()
+{
+	return 0;
+}
+
+template<typename... Args>
+static inline constexpr unsigned
+CountNameValuePairs(gcc_unused const char *name, gcc_unused const char *value,
+		    Args... args)
+{
+	return 1 + CountNameValuePairs(args...);
+}
+
+/**
+ * A wrapper for UpnpMakeAction() that counts the number of name/value
+ * pairs and adds the nullptr sentinel.
+ */
+template<typename... Args>
+static inline IXML_Document *
+MakeActionHelper(const char *action_name, const char *service_type,
+		 Args... args)
+{
+	const unsigned n = CountNameValuePairs(args...);
+	return UpnpMakeAction(action_name, service_type, n,
+			      args...,
+			      nullptr, nullptr);
+}
+
+#endif

src/db/upnp/ContentDirectoryService.cxx

@@ -24,12 +24,11 @@
 #include "ixmlwrap.hxx"
 #include "Directory.hxx"
 #include "Util.hxx"
+#include "Action.hxx"
 #include "util/Error.hxx"
 
 #include <stdio.h>
 
-#include <upnp/upnptools.h>
-
 ContentDirectoryService::ContentDirectoryService(const UPnPDevice &device,
 						 const UPnPService &service)
 	:m_actionURL(caturl(device.URLBase, service.controlURL)),
@@ -80,17 +79,15 @@ ContentDirectoryService::readDirSlice(UpnpClient_Handle hdl,
 	char ofbuf[100], cntbuf[100];
 	sprintf(ofbuf, "%d", offset);
 	sprintf(cntbuf, "%d", count);
-	int argcnt = 6;
 	// Some devices require an empty SortCriteria, else bad params
 	IXML_Document *request =
-		UpnpMakeAction("Browse", m_serviceType.c_str(), argcnt,
+		MakeActionHelper("Browse", m_serviceType.c_str(),
 				 "ObjectID", objectId,
 				 "BrowseFlag", "BrowseDirectChildren",
 				 "Filter", "*",
 				 "SortCriteria", "",
 				 "StartingIndex", ofbuf,
-			       "RequestedCount", cntbuf,
-			       nullptr, nullptr);
+				 "RequestedCount", cntbuf);
 	if (request == nullptr) {
 		error.Set(upnp_domain, "UpnpMakeAction() failed");
 		return false;
@@ -165,18 +162,15 @@ ContentDirectoryService::search(UpnpClient_Handle hdl,
 	while (offset < total) {
 		char ofbuf[100];
 		sprintf(ofbuf, "%d", offset);
-		// Create request
-		int argcnt = 6;
 
 		IXML_Document *request =
-			UpnpMakeAction("Search", m_serviceType.c_str(), argcnt,
+			MakeActionHelper("Search", m_serviceType.c_str(),
 					 "ContainerID", objectId,
 					 "SearchCriteria", ss,
 					 "Filter", "*",
 					 "SortCriteria", "",
 					 "StartingIndex", ofbuf,
-				       "RequestedCount", "0", // Setting a value here gets twonky into fits
-				       nullptr, nullptr);
+					 "RequestedCount", "0"); // Setting a value here gets twonky into fits
 		if (request == 0) {
 			error.Set(upnp_domain, "UpnpMakeAction() failed");
 			return false;
@@ -270,16 +264,14 @@ ContentDirectoryService::getMetadata(UpnpClient_Handle hdl,
 				     Error &error)
 {
 	// Create request
-	int argcnt = 6;
 	IXML_Document *request =
-		UpnpMakeAction("Browse", m_serviceType.c_str(), argcnt,
+		MakeActionHelper("Browse", m_serviceType.c_str(),
 				 "ObjectID", objectId,
 				 "BrowseFlag", "BrowseMetadata",
 				 "Filter", "*",
 				 "SortCriteria", "",
 				 "StartingIndex", "0",
-			       "RequestedCount", "1",
-			       nullptr, nullptr);
+				 "RequestedCount", "1");
 	if (request == nullptr) {
 		error.Set(upnp_domain, "UpnpMakeAction() failed");
 		return false;