fix: check if the custom channel's server address is valid

channel/custom.go

@@ -3,6 +3,7 @@ package channel
 import (
 	"bytes"
 	"errors"
+	"message-pusher/common"
 	"message-pusher/model"
 	"net/http"
 	"strings"
@@ -13,6 +14,9 @@ func SendCustomMessage(message *model.Message, user *model.User, channel_ *model
 	if strings.HasPrefix(url, "http:") {
 		return errors.New("自定义通道必须使用 HTTPS 协议")
 	}
+	if strings.HasPrefix(url, common.ServerAddress) {
+		return errors.New("自定义通道不能使用本服务地址")
+	}
 	template := channel_.Other
 	template = strings.Replace(template, "$url", message.URL, -1)
 	template = strings.Replace(template, "$to", message.To, -1)