DOCKER_CONFIG env var is parsed inconsistently and incorrectly in fromDockerConfig / fromDockerContext

lib/docker-client.ts の fromDockerConfig と fromDockerContext から始め、各エントリポイントが DOCKER_CONFIG とデフォルトのホームディレクトリパスをどのように解決しているかを追ってください。完了条件は、DOCKER_CONFIG が設定されていない場合の動作を維持しつつ、両方のエントリポイントが config.json と contexts のパスを含め、Docker の設定ディレクトリを一貫して使用することです。

DOCKER_CONFIG is the path to Docker's config directory (default ~/.docker), but docker-client.ts interprets it two different ways, and neither matches that.

1. fromDockerConfig treats it as the path to config.json

https://github.com/docker/node-sdk/blob/a4d38673441c1463870fe3ba7c77c067f0bf1e46/lib/docker-client.ts#L267-L270

const configPath =
    process.env.DOCKER_CONFIG ||
    join(homedir(), '.docker', 'config.json');

With DOCKER_CONFIG=/etc/docker-config, this does readFile('/etc/docker-config', 'utf8') on a directory, which fails with EISDIR. That is not ENOENT, so the "config file doesn't exist, use default" branch below doesn't catch it either — the error propagates and fromDockerConfig() throws instead of connecting. It should be join(configDir, 'config.json').

2. fromDockerContext treats it as a directory, then appends .docker

https://github.com/docker/node-sdk/blob/a4d38673441c1463870fe3ba7c77c067f0bf1e46/lib/docker-client.ts#L180-L182

const configDir = process.env.DOCKER_CONFIG || homedir();
const contextsDir = join(configDir, '.docker', 'contexts', 'meta');
const tlsDir = join(configDir, '.docker', 'contexts', 'tls');

The .docker component is only correct for the homedir() fallback. With DOCKER_CONFIG=/etc/docker-config this looks in /etc/docker-config/.docker/contexts/meta rather than /etc/docker-config/contexts/meta, so context lookup fails with Docker contexts directory not found.

The two readings are mutually inconsistent — at most one could be right for a given value of the variable.

Expected

Both should resolve the config directory the same way, e.g.

const configDir = process.env.DOCKER_CONFIG || join(homedir(), '.docker');
// config.json  -> join(configDir, 'config.json')
// contexts     -> join(configDir, 'contexts', 'meta') / join(configDir, 'contexts', 'tls')

This matches the CLI: https://docs.docker.com/reference/cli/docker/#environment-variables

Notes

Neither path misbehaves when DOCKER_CONFIG is unset, which is presumably why it hasn't come up. Affects main as of a4d3867.

Found while adapting the connection logic in docker-client.ts for another client; I haven't opened a PR. This report was written by Claude (AI-generated) and reviewed by me before filing.