[BUG] unexpected character "-" in variable name since v2.29.3

[bwaldvogel]

Description

Environment variables defined via an env_file that have "-" characters in their name get refused after updating docker-compose from v2.29.2 to v2.29.3

Steps To Reproduce

services:
  env_runner:
    image: alpine
    command: env
    env_file:
      - ./myenv.env

myenv.env

foo-bar=test

Expected behaviour (v2.29.2)

$ docker compose up
[+] Running 1/1
 ✔ Container env_runner-1      Created
Attaching to env_runner-1
[…]
env_runner-1  | foo-bar=test
env_runner-1 exited with code 0

Actual behaviour (v2.29.3)

$ docker compose up
failed to read myenv.env: line 1: unexpected character "-" in variable name "foo-bar=test"

Compose Version

Docker Compose version 2.29.3

Docker Environment

Client:
 Version:           27.2.0
 API version:       1.47
 Go version:        go1.23.0
 Git commit:        3ab4256958
 Built:             Thu Aug 29 16:44:26 2024
 OS/Arch:           linux/amd64
 Context:           default

Server:
 Engine:
  Version:          27.2.0
  API version:      1.47 (minimum version 1.24)
  Go version:       go1.23.0
  Git commit:       3ab5c7d003
  Built:            Thu Aug 29 16:44:26 2024
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.7.22
  GitCommit:        7f7fdf5fed64eb6a7caf99b3e12efcf9d60e311c.m
 runc:
  Version:          1.1.14
  GitCommit:        
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Anything else?

No response

[thaJeztah]

While technically Linux can use env-vars with hyphens as name (any character except nul terminators), it's generally recommended to only use characters from the portable character set; https://pubs.opengroup.org/onlinepubs/7908799/xbd/envvar.html

What I suspect happened here is that the libary used by compose possibly considers them as invalid formatted substitution character, and the part after the hyphen as default; https://tldp.org/LDP/abs/html/parameter-substitution.html

That said, env_file for services should follow the same rules as --env-file on docker run (which only considers = as separator, and performs no substitution/validation otherwise 🤔

[thaJeztah]

This looks related to this PR;

• compose-spec/compose-go#680

However the env_file (docker run --env-file) should not do interpolation; is there a way to make that conditional, @ndeloof ?

docker run --rm --env "hello-world=hello-value" alpine printenv hello-world
hello-value

For reference; this is the validation in the OCI runtime (runc); https://github.com/opencontainers/runc/blob/7c2e69f1c4a7df1cf4690ccfc68c0a3857251d12/libcontainer/init_linux.go#L258-L281

// populateProcessEnvironment loads the provided environment variables into the
// current processes's environment.
func populateProcessEnvironment(env []string) error {
	for _, pair := range env {
		p := strings.SplitN(pair, "=", 2)
		if len(p) < 2 {
			return errors.New("invalid environment variable: missing '='")
		}
		name, val := p[0], p[1]
		if name == "" {
			return errors.New("invalid environment variable: name cannot be empty")
		}
		if strings.IndexByte(name, 0) >= 0 {
			return fmt.Errorf("invalid environment variable %q: name contains nul byte (\\x00)", name)
		}
		if strings.IndexByte(val, 0) >= 0 {
			return fmt.Errorf("invalid environment variable %q: value contains nul byte (\\x00)", name)
		}
		if err := os.Setenv(name, val); err != nil {
			return err
		}
	}
	return nil
}

[ndeloof]

env-file when used in compose does support interpolation (and a bunch of our users rely on this feature)

[thaJeztah]

Right, but the reverse also looks to be true; it's rejecting env-vars that should be considered valid 🤔

[ndeloof]

Environment variable names used by the utilities in the Shell and Utilities volume of IEEE Std 1003.1-2001 consist solely of uppercase letters, digits, and the '_' (underscore) from the characters defined in Portable Character Set and do not begin with a digit. Other characters may be permitted by an implementation;

So - MAY be permitted, and I can guess some will rely on it. To get actual support of this, we will have to make the dotenv parser way more flexible that it is 😓

[thaJeztah]

Yeah, I recall we once added validation for environment-variables, but then had to revert, for similar reasons;

• moby/moby#16585
• moby/moby#16608

[bwaldvogel]

When will the fix be published? I’ve tested docker compose v2.29.7 and I still get the same error.