Implement group redirection.

README

@@ -75,7 +75,9 @@ fields, all of which are optional.
  - `allow-recording`: if true, then recording is allowed in this group;
  - `allow-anonymous`: if true, then users may connect with an empty
    username; this is not recommended, since anonymous users are not
-   allowed to participate in the chat.
+   allowed to participate in the chat;
+ - `redirect`: if set, then attempts to join the group will be redirected
+   to the given URL; most other fields are ignored in this case.
    
 A user definition is a dictionary with the following fields:
 

group.go

@@ -334,6 +334,7 @@ type groupDescription struct {
 	loadTime       time.Time           `json:"-"`
 	modTime        time.Time           `json:"-"`
 	fileSize       int64               `json:"-"`
+	Redirect       string              `json:"redirect,omitempty"`
 	Public         bool                `json:"public,omitempty"`
 	MaxClients     int                 `json:"max-clients,omitempty"`
 	AllowAnonymous bool                `json:"allow-anonymous,omitempty"`

webclient.go

@@ -709,6 +709,12 @@ func startClient(conn *websocket.Conn) (err error) {
 		}
 		return
 	}
+	if g.description.Redirect != "" {
+		// We normally redirect at the HTTP level, but the group
+		// description could have been edited in the meantime.
+		err = userError("group is now at " + g.description.Redirect)
+		return
+	}
 	c.group = g
 	defer delClient(c)
 

webserver.go

@@ -93,7 +93,7 @@ func groupHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	_, err := addGroup(name, nil)
+	g, err := addGroup(name, nil)
 	if err != nil {
 		if os.IsNotExist(err) {
 			http.NotFound(w, r)
@@ -104,6 +104,13 @@ func groupHandler(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
+
+	if g.description.Redirect != "" {
+		http.Redirect(w, r, g.description.Redirect,
+			http.StatusPermanentRedirect)
+		return
+	}
+
 	http.ServeFile(w, r, filepath.Join(staticRoot, "sfu.html"))
 }