`{file.*}` placeholder is not replaced with file content in named matcher

[axeleroy]

Issue Details

Hello,

I'm trying to block access to clients based on their user agent, using the header_regexp matcher. I originally put the regexp in my Caddyfile but decided to move it in another file located at /etc/caddy/bots-list.txt and to use the {file.*} placeholder to read its content:

(noscrap) {
  # Originally was 
  # @botForbidden header_regexp User-Agent "AI2Bot|AI2Bot-DeepResearchEval|..."
  @botForbidden header_regexp User-Agent {file./etc/caddy/bots-list.txt}

  handle @botForbidden  {
    respond /* "Access denied" 403 {
      close
    }
  }
}

foo.example.com {
  reverse_proxy 172.22.0.14:5000
  import noscrap
}

The issue is that live config does not reflect the content of bots-list.txt:

$ curl "http://localhost:2019/config/"
{
  "admin": {
    "listen": "tcp/localhost:2019"
  },
  "apps": {
    "http": {
      "servers": {
        "srv0": {
          "listen": [
            ":443"
          ],
          "routes": [
            {
              "handle": [
                {
                  "handler": "subroute",
                  "routes": [
                    {
                      "group": "group24",
                      "handle": [
                        {
                          "handler": "subroute",
                          "routes": [
                            {
                              "handle": [
                                {
                                  "body": "Access denied",
                                  "close": true,
                                  "handler": "static_response",
                                  "status_code": 403
                                }
                              ],
                              "match": [
                                {
                                  "path": [
                                    "/*"
                                  ]
                                }
                              ]
                            }
                          ]
                        }
                      ],
                      "match": [
                        {
                          "header_regexp": {
                            "User-Agent": {
                              "name": "botForbidden",
                              "pattern": "{file./etc/caddy/bots-list.txt}"
                            }
                          }
                        }
                      ]
                    },
                    {
                      "handle": [
                        {
                          "handler": "reverse_proxy",
                          "upstreams": [
                            {
                              "dial": "172.22.0.14:5000"
                            }
                          ]
                        }
                      ]
                    }
                  ]
                }
              ],
              "match": [
                {
                  "host": [
                    "foo.example.com"
                  ]
                }
              ],
              "terminal": true
            }
          ]
        }
      }
    }
  }
}

You can see that the matcher botForbidden read "pattern": "{file./etc/caddy/bots-list.txt}" when I expect it to read "pattern": "AI2Bot|AI2Bot-DeepResearchEval|..."

I have search across GitHub and the forum but found nothing similar to my issue, making me wonder if this is a bug.

Assistance Disclosure

AI not used

If AI was used, describe the extent to which it was used.

No response

[steadytao]

header_regexp patterns are static config and are compiled during provisioning while {file.*} is a runtime placeholder provider so it is not expanded into the regexp pattern during Caddyfile -> JSON adaptation.

For this use case, use a parse-time mechanism instead, either import a file containing the matcher line itself or use {$ENV} if the regexp can be supplied as one token. I think this may be better suited for the forum unless we want to turn it into a docs clarification or feature request.

[axeleroy]

Hello,

Thank you for the clarification. Maybe it needs to be explained in the docs, as I don't remember reading about runtime and parse-time placeholders and matchers.

[steadytao]

I do agree the docs could explain it slightly more thoroughly so I have created the above PR.