feat: add env prefix option

[dderevjanik]

This pull request introduces a new feature to env store prefix, allowing environment variables to be filtered and stripped of a specified prefix.

ref #157

based on https://www.dynaconf.com/envvars/

[dderevjanik]

Hi @indexzero,

just wanted to kindly follow up on this PR to see if there’s anything else I can do to help move it forward? Thank you :)

[dderevjanik]

Hi @mhamann,

just wanted to kindly follow up on this PR to see if there’s anything else I can do to help move it forward? Thank you :)

[mhamann]

Hey @dderevjanik, thanks for your submission. Seems like a good feature that adds some parity with libraries in other languages. I'll go ahead and merge it, but it may take a bit of time to get it released due to my current workload.

[rodw]

@mhamann thanks for merging this enhancement and for the nconf library in general

would it be possible to publish a new release of nconf to npm to make this feature available for import?

[mhamann]

I'll try to get this released by end of week. Thanks!

[rodw]

Thanks again @mhamann I appreciate the work you have and continue to put in on this module.

Incidentally, as may already be obvious to some in this thread, I realized that one can emulate this prefix-stripping (and the corresponding "ignore everything without the prefix) behavior by adding a transform to the env() options map.

E.g. something like this:

// the prefix to strip from env var keys; e.g., `foo_bar` -> `bar`
const envVarPrefix = "foo_";

// when true, only include env vars that start with the prefix
const excludeWhenMissingPrefix = true;

const envOptions = {
  transform: (pair: { key: string, value: unknown }): { key: string, value: unknown } | null => {
    if (pair.key.startsWith(envVarPrefix)) {
      pair.key = pair.key.substring(envVarPrefix.length);
      return pair;
    } else {
      return excludeWhenMissingPrefix ? null : pair;
    }
  }
}

nconf.env(envOptions);

This prefix flag in PR#428 is more convenient and straightforward than a custom transform, but it's hard to overstate how powerful/flexible the transform functions are

[dderevjanik]

@rodw You're absolutely right that the transform function provides a powerful way to modify environment variable keys dynamically. However, one key limitation is that using transform prevents you from leveraging parseValues and separator, since transform overrides the default processing logic.

const envOptions = {
  prefix: "foo_",
  separator: "__",
  parseValues: true
};

nconf.env(envOptions);

With this PR, the prefix option allows you to strip a prefix while still benefiting from parseValues and separator (and others aswell).

This approach keeps the configuration clean and declarative while avoiding the need for a custom transform function. It ensures that prefix stripping works seamlessly with other nconf features rather than requiring trade-offs.

[dderevjanik]

Hi @mhamann,

Just checking in, do you have any plans to make a new release that includes this feature?

Thanks in advance! :)

[mhamann]

This is now released in v0.13 and v1.0.0-beta.2

[dderevjanik]

Hi @mhamann, thanks for releasing v0.13!
Unfortunately, it looks like there was a bad merge: c0c8787.
The line this.prefix = options.prefix || ''; is missing, which causes the code not to work at all.

[mhamann]

Hmm, interesting. All of the tests pass. Are we missing coverage there?