问 如何在Promtail中解析嵌套的json

EN

我有以下日志，它是嵌套的JSON

{"level":30,"time":1627625600625,"pid":15676,"hostname":"admin-hp-elitebook-840-g2","reqId":"req-2","req":{"method":"POST","url":"/v1/login","hostname":"127.0.0.1:3000","remoteAddress":"127.0.0.1","remotePort":55884},"msg":"incoming request"}

然后，我想为method、URL、host创建标签。我尝试了在promtail中使用如下JSON表达式。我尝试解析JSON，但我可以提取请求，但我不知道如何解析promtail中嵌套JSON

scrape_configs:
- job_name: plainlog
  pipeline_stages:
  - json:
      expressions:
        req: req
  - labels:
  - output:
      source: req
  static_configs:
  - targets:
      - localhost
    labels:
      job: plainlog
      __path__: /home/nidhin/Desktop/plainlog/*log