service: add user status

This lists all the users of the instances, along with the number
of networks they have.

Limited to 50 users to avoid flooding with thousands of messages
on large instances.

doc/soju.1.scd

@@ -407,6 +407,9 @@ character.
 	*-network* <name>
 		Select a network. By default, the current network is selected, if any.
 
+*user status*
+	Show a list of users on this server. Only admins can query this information.
+
 *user create* -username <username> -password <password> [options...]
 	Create a new soju user. Only admin users can create new accounts.
 	The _-username_ and _-password_ flags are mandatory.

service.go

@@ -272,6 +272,11 @@ func init() {
 		},
 		"user": {
 			children: serviceCommandSet{
+				"status": {
+					desc:   "show a list of users and their current status",
+					handle: handleUserStatus,
+					admin:  true,
+				},
 				"create": {
 					usage:  "-username <username> -password <password> [-realname <realname>] [-admin]",
 					desc:   "create a new soju user",
@@ -874,6 +879,40 @@ func handleServiceSASLReset(ctx *serviceContext, params []string) error {
 	return nil
 }
 
+func handleUserStatus(ctx *serviceContext, params []string) error {
+	// Limit to a small amount of users to avoid sending
+	// thousands of messages on large instances.
+	users := make([]database.User, 0, 50)
+
+	ctx.user.srv.lock.Lock()
+	n := len(ctx.user.srv.users)
+	for _, user := range ctx.user.srv.users {
+		if len(users) == cap(users) {
+			break
+		}
+		users = append(users, user.User)
+	}
+	ctx.user.srv.lock.Unlock()
+
+	for _, user := range users {
+		line := user.Username
+		if user.Admin {
+			line += " (admin)"
+		}
+		networks, err := ctx.user.srv.db.ListNetworks(ctx, user.ID)
+		if err != nil {
+			return fmt.Errorf("could not get networks of user %q: %v", user.Username, err)
+		}
+		line += fmt.Sprintf(": %d networks", len(networks))
+		ctx.print(line)
+	}
+	if n > len(users) {
+		ctx.print(fmt.Sprintf("(%d more users omitted)", n-len(users)))
+	}
+
+	return nil
+}
+
 func handleUserCreate(ctx *serviceContext, params []string) error {
 	fs := newFlagSet()
 	username := fs.String("username", "", "")