http: enclose libevent-dependent code in a namespace

This commit is a no-op to isolate HTTP methods and objects that
depend on libevent. Following commits will add replacement objects
and methods in a new namespace for testing and review before
switching over the server.

src/httpserver.h

@@ -30,6 +30,8 @@ static const int DEFAULT_HTTP_SERVER_TIMEOUT=30;
 struct evhttp_request;
 struct event_base;
 class CService;
+
+namespace http_libevent {
 class HTTPRequest;
 
 /** Initialize HTTP server.
@@ -48,9 +50,10 @@ void StopHTTPServer();
 
 /** Change logging level for libevent. */
 void UpdateHTTPServerLogging(bool enable);
+} // namespace http_libevent
 
 /** Handler for requests to a certain HTTP path */
-typedef std::function<void(HTTPRequest* req, const std::string &)> HTTPRequestHandler;
+typedef std::function<void(http_libevent::HTTPRequest* req, const std::string &)> HTTPRequestHandler;
 /** Register handler for prefix.
  * If multiple handlers match a prefix, the first-registered one will
  * be invoked.
@@ -59,6 +62,7 @@ void RegisterHTTPHandler(const std::string &prefix, bool exactMatch, const HTTPR
 /** Unregister handler for prefix */
 void UnregisterHTTPHandler(const std::string &prefix, bool exactMatch);
 
+namespace http_libevent {
 /** Return evhttp event base. This can be used by submodules to
  * queue timers or custom events.
  */
@@ -158,6 +162,7 @@ public:
  * @param[in] key represents the query parameter of which the value is returned
  */
 std::optional<std::string> GetQueryParameterFromUri(const char* uri, const std::string& key);
+} // namespace http_libevent
 
 /** Event class. This can be used either as a cross-thread trigger or as a timer.
  */