Correctly extract mysql users.settings json type to `UserSettings…

…` type

server/datastore/mysql/users.go

@@ -326,11 +326,10 @@ func (ds *Datastore) UserSettings(ctx context.Context, userID uint) (*fleet.User
 	`
 	err := sqlx.GetContext(ctx, ds.reader(ctx), &bytes, stmt, userID)
 	if err != nil {
-		// okay for a user not to have any settings
 		if err == sql.ErrNoRows {
-			return settings, nil
+			return nil, ctxerr.Wrap(ctx, notFound("UserSettings").WithID(userID))
 		}
-		return nil, ctxerr.Wrap(ctx, err, "selecting app config")
+		return nil, ctxerr.Wrap(ctx, err, "selecting user settings")
 	}
 
 	if len(bytes) == 0 {

server/fleet/users.go

@@ -37,7 +37,20 @@ type User struct {
 }
 
 type UserSettings struct {
-	HiddenHostsTableColumns *[]string `json:"hidden_hosts_table_columns,omitempty"`
+	HiddenHostsTableColumns []string `json:"hidden_hosts_table_columns,omitempty"`
+}
+
+// Scan implements the sql.Scanner interface, tells DB driver how to convert MySQL type (json) to
+// custom Go type (UserSettings).
+func (us *UserSettings) Scan(val interface{}) error {
+	switch v := val.(type) {
+	case []byte:
+		return json.Unmarshal(v, us)
+	case string:
+		return json.Unmarshal([]byte(v), us)
+	default:
+		return fmt.Errorf("unsupported type: %T", v)
+	}
 }
 
 // IsGlobalObserver returns true if user is either a Global Observer or a Global Observer+