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/chat.go

@@ -41,6 +41,12 @@ func GetClientsForUser(userID string) ([]*Client, error) {
 	return clients[userID], nil
 }
 
+// FindClientByID will return a single connected client by ID.
+func FindClientByID(clientID uint) (*Client, bool) {
+	client, found := _server.clients[clientID]
+	return client, found
+}
+
 // GetClients will return all the current chat clients connected.
 func GetClients() []*Client {
 	clients := []*Client{}
@@ -105,6 +111,13 @@ func SendAllWelcomeMessage() {
 	_server.sendAllWelcomeMessage()
 }
 
+// SendSystemMessageToClient will send a single message to a single connected chat client.
+func SendSystemMessageToClient(clientID uint, text string) {
+	if client, foundClient := FindClientByID(clientID); foundClient {
+		_server.sendSystemMessageToClient(client, text)
+	}
+}
+
 // Broadcast will send all connected clients the outbound object provided.
 func Broadcast(event events.OutboundEvent) error {
 	return _server.Broadcast(event.GetBroadcastPayload())