MM-24037 Adding getKnowUsers API endpoint (#14332)

* Adding getKnowUsers API endpoint

* Adding i18n strings

* Fixing golint errors

* Adding doc strings

* Remove debug line

* Updating app_iface

* Fixing gofmt

api4/user.go

@@ -26,6 +26,7 @@ func (api *API) InitUser() {
 	api.BaseRoutes.Users.Handle("", api.ApiSessionRequired(getUsers)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/ids", api.ApiSessionRequired(getUsersByIds)).Methods("POST")
 	api.BaseRoutes.Users.Handle("/usernames", api.ApiSessionRequired(getUsersByNames)).Methods("POST")
+	api.BaseRoutes.Users.Handle("/known", api.ApiSessionRequired(getKnownUsers)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/search", api.ApiSessionRequiredDisableWhenBusy(searchUsers)).Methods("POST")
 	api.BaseRoutes.Users.Handle("/autocomplete", api.ApiSessionRequired(autocompleteUsers)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/stats", api.ApiSessionRequired(getTotalUsersStats)).Methods("GET")
@@ -717,6 +718,18 @@ func getUsersByNames(c *Context, w http.ResponseWriter, r *http.Request) {
 	w.Write([]byte(model.UserListToJson(users)))
 }
 
+func getKnownUsers(c *Context, w http.ResponseWriter, r *http.Request) {
+	userIds, err := c.App.GetKnownUsers(c.App.Session().UserId)
+	if err != nil {
+		c.Err = err
+		return
+	}
+
+	data, _ := json.Marshal(userIds)
+
+	w.Write(data)
+}
+
 func searchUsers(c *Context, w http.ResponseWriter, r *http.Request) {
 	props := model.UserSearchFromJson(r.Body)
 	if props == nil {