httpgateway: set new max payload length config value

config.cpp

@@ -53,6 +53,17 @@ int Config::optional(const std::string &key, int defaultvalue)
 	return defaultvalue;
 }
 
+uint64_t Config::optional(const std::string &key, uint64_t defaultvalue)
+{
+	auto it = this->configmap.find(key);
+	if(it != this->configmap.end())
+	{
+		std::string str = it->second;
+		return static_cast<uint64_t>(std::stoull(str));
+	}
+	return defaultvalue;
+}
+
 Config::Config(const std::map<std::string, std::string> &map)
 {
 
@@ -93,6 +104,8 @@ Config::Config(const std::map<std::string, std::string> &map)
 	this->anon_permissions = Permissions(required("anon_permissions"));
 
 	this->templateprefix = "{qswiki:";
+
+	this->max_payload_length = optional("max_payload_length", 10 * 1024 * 1024);
 }
 
 ConfigReader::ConfigReader(const std::string &file)