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

Start in lib/docker-client.ts at fromDockerConfig and fromDockerContext, then trace how each entry point resolves DOCKER_CONFIG and the default home-directory path. Done means both entry points use the Docker config directory consistently, including config.json and contexts paths, while preserving behavior when DOCKER_CONFIG is unset.

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.