Issues with path_regexp

Help
1

Hi all!

1. The problem I’m having:

I try to reproduce the examples in the documentation for path_regexp (Request matchers (Caddyfile) — Caddy Documentation). The first two example work, but the third entry produces an error i do not understand. The entry is:

@static `path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()`

2. Error messages and/or full log output:

Caddy does not start any more log output (with docker compose logs) is:

caddy-1  | {"level":"info","ts":1749055527.8660698,"msg":"maxprocs: Leaving GOMAXPROCS=4: CPU quota undefined"}
caddy-1  | {"level":"info","ts":1749055527.8662655,"msg":"GOMEMLIMIT is updated","package":"github.com/KimMachineGun/automemlimit/memlimit","GOMEMLIMIT":3758340096,"previous":9223372036854775807}
caddy-1  | {"level":"info","ts":1749055527.8663309,"msg":"using config from file","file":"/etc/caddy/Caddyfile"}
caddy-1  | {"level":"info","ts":1749055527.8670762,"msg":"adapted config to JSON","adapter":"caddyfile"}
caddy-1  | {"level":"info","ts":1749055527.868077,"logger":"admin","msg":"admin endpoint started","address":"localhost:2019","enforce_origin":false,"origins":["//localhost:2019","//[::1]:2019","//127.0.0.1:2019"]}
caddy-1  | {"level":"info","ts":1749055527.8682792,"logger":"tls.cache.maintenance","msg":"started background certificate maintenance","cache":"0x4000527e80"}
caddy-1  | {"level":"info","ts":1749055527.8723888,"logger":"tls.cache.maintenance","msg":"stopped background certificate maintenance","cache":"0x4000527e80"}
caddy-1  | {"level":"info","ts":1749055527.8724382,"msg":"maxprocs: No GOMAXPROCS change to reset"}
caddy-1  | Error: loading initial config: loading new config: loading http app module: provision http: server srv0: setting up route matchers: route 0: loading matcher modules: module name 'expression': provision http.matchers.expression: compiling CEL program: ERROR: <input>:1:13: Syntax error: token recognition error at: ''\.'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ............^
caddy-1  | ERROR: <input>:1:17: matcher argument must be a string literal
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ................^
caddy-1  | ERROR: <input>:1:25: Syntax error: mismatched input '{' expecting ')'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ........................^
caddy-1  | ERROR: <input>:1:29: Syntax error: token recognition error at: '\'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ............................^
caddy-1  | ERROR: <input>:1:31: Syntax error: no viable alternative at input '.('
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ..............................^
caddy-1  | ERROR: <input>:1:35: Syntax error: token recognition error at: '|j'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ..................................^
caddy-1  | ERROR: <input>:1:39: Syntax error: token recognition error at: '$'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | ......................................^
caddy-1  | ERROR: <input>:1:40: Syntax error: token recognition error at: '') && file()'
caddy-1  |  | path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()
caddy-1  |  | .......................................^

3. Caddy version:

docker compose exec caddy caddy version
v2.10.0 h1:fonubSaQKF1YANl8TXqGcn4IbIRUDdfAkpcsfI/vX5U=

4. How I installed and ran Caddy:

a. System environment:

uname -a
Linux rpi5b 6.12.22-current-bcm2711 #1 SMP PREEMPT Wed Apr 23 13:38:58 UTC 2025 aarch64 GNU/Linux

cat /etc/debian_version 
12.10

docker --version
Docker version 28.2.2, build e6534b4

b. Command:

docker compose start

c. Service/unit/compose file:

name: "test"
services:

  caddy:
    image: caddy:latest
    ports:
      - "80:80"
    volumes:
      - ./data:/data
      - ./Caddyfile:/etc/caddy/Caddyfile

d. My complete Caddy config:

:80 {
	@static `path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()`

	respond @static "Does not work"
}

5. Links to relevant resources:

2

file needs a root directive. Without it, Caddy doesn’t know where to look for the file.

1 Like
3

The error message hints more on a problem with the regular expression. However i tried the following two config files and the error message stays exactly the same:

:80 {
	route * /var/www/
	@static `path_regexp('\.([a-f0-9]{6})\.(css|js)$') && file()`

	respond @static "Does not work"
}

and

:80 {
	@static `path_regexp('\.([a-f0-9]{6})\.(css|js)$')`

	respond @static "Does not work"
}

also the variants from the examples without CEL do work:

:80 {
	@static path_regexp static \.([a-f0-9]{6})\.(css|js)$

	respond @static "Does work"
}

and

:80 {
	@static path_regexp \.([a-f0-9]{6})\.(css|js)$

	respond @static "Does work"
}
4

I wonder if escaping the backslashes is missed. Can you try this?

@static `path_regexp('\\.([a-f0-9]{6})\\.(css|js)$') && file()`
1 Like
5

Hi Mohammed,

thank you very much for your answer, this was the solution and works as intended. Is the escaping of the backslash necessary because the expression is parsed first as CEL and then as regexp?

6

That was my assumption, but I haven’t traced the code enough to be sure.