Feature/oc 1316 add support for system message to single user (#1351)

* add public func to lookup a ChatClient by its clientId

* add facility to send a system message directly to a user

* add clientId field to UserEvent

* implement simple http endpoint to send a message to a user

* let mux handle new directSystemMessageToUser endpoint

* add ClientId to UserEvents across the codebase

* render body of system-message to client

* add clientId to Chat-Message

* add tests showing how url-parsing should work

* add simple rest endpoint helpers for parameter-parsing and easy routing

* use newly added rest-endpoint helper to rout to Client-Messaging controller

* use safe "ReadRestUrlParameter" to parse ClientId

* remove empty HandleFunc in router

* set Header directly to prevent built-in (platform-dependent) canonicalization to kick in

* fix typo in "Parameter" message

* remove debug-logging of HTTP headers in REST-helpers

* convert to uint32 to prevent overruns when converting to wraptype uint later on

* resolve linter-ouchies

* resolve linter potential nil-deref warning

* document the SendSystemMessageToClient endpoint in swaggerdoc

* remove clientId assignment causing potential nil dereference in userDisabledEvent-case

as the clientId isn't relevant here anyway

* make findClientById private, so its not accessible outside of core/chat

* remove redundant string type hint

* Update PR based on linter requirements

Co-authored-by: Raffael Rehberger <raffael@rtrace.io>
Co-authored-by: Gabe Kangas <gabek@real-ity.com>

core/chat/server.go

@@ -115,6 +115,7 @@ func (s *Server) sendUserJoinedMessage(c *Client) {
 	userJoinedEvent := events.UserJoinedEvent{}
 	userJoinedEvent.SetDefaults()
 	userJoinedEvent.User = c.User
+	userJoinedEvent.ClientID = c.id
 
 	if err := s.Broadcast(userJoinedEvent.GetBroadcastPayload()); err != nil {
 		log.Errorln("error adding client to chat server", err)
@@ -317,6 +318,7 @@ func (s *Server) sendSystemMessageToClient(c *Client, message string) {
 		},
 	}
 	clientMessage.SetDefaults()
+	clientMessage.RenderBody()
 	s.Send(clientMessage.GetBroadcastPayload(), c)
 }