OpenFeature

Use showwhat as the evaluation engine behind the standard OpenFeature Server SDK. The @showwhat/openfeature package provides a Provider that bridges OpenFeature evaluations to showwhat's rule engine.

npm install @showwhat/openfeature @openfeature/server-sdk

@openfeature/server-sdk is a peer dependency.

Quick start

import { OpenFeature } from "@openfeature/server-sdk";
import { ShowwhatProvider } from "@showwhat/openfeature";
import { MemoryData } from "showwhat";

const data = await MemoryData.fromYaml(yamlString);

await OpenFeature.setProviderAndWait(new ShowwhatProvider({ data }));

const client = OpenFeature.getClient();

const enabled = await client.getBooleanValue("checkout_v2", false, {
  env: "production",
});

Provider options

Option	Type	Required	Description
data	DefinitionReader	yes	Source of showwhat definitions
evaluators	ConditionEvaluators	no	Custom condition evaluators (see Custom Conditions)
deps	Dependencies	no	Runtime utilities forwarded to all evaluator calls
logger	Logger	no	Logger instance for debug output

import { ShowwhatProvider } from "@showwhat/openfeature";
import { MemoryData, registerEvaluators } from "showwhat";

const data = await MemoryData.fromObject({
  definitions: {
    premium_feature: {
      variations: [{ value: true, conditions: [{ type: "tier", tier: "pro" }] }, { value: false }],
    },
  },
});

const provider = new ShowwhatProvider({
  data,
  evaluators: registerEvaluators({ tier: tierEvaluator }),
  deps: { hash: murmurhash.v3 },
});

Shared lifetime

Since deps is stored on the provider instance, the same object is shared across all evaluations for the lifetime of the provider. This is appropriate for stateless functions (hash, fetch). If you need per-call deps, extend ShowwhatProvider or wrap it in a factory.

Context mapping

OpenFeature's EvaluationContext is flattened into showwhat's Context (a flat Record<string, string | number | boolean>). Nested objects, arrays, dates, and null values are dropped. The targetingKey field is passed through as-is.

const result = await client.getBooleanValue("my_flag", false, {
  targetingKey: "user-123",
  env: "production",
  admin: true,
});

// showwhat sees: { targetingKey: "user-123", env: "production", admin: true }

Evaluation types

All four OpenFeature evaluation types are supported:

Method	showwhat value type
resolveBooleanEvaluation	boolean
resolveStringEvaluation	string
resolveNumberEvaluation	number
resolveObjectEvaluation	JsonValue (object, array, or null)

If the resolved value does not match the requested type, the provider returns the defaultValue with a TYPE_MISMATCH error.

Error mapping

showwhat errors are mapped to OpenFeature error codes:

showwhat error	OpenFeature error code
DefinitionNotFoundError	FLAG_NOT_FOUND
DefinitionInactiveError	FLAG_NOT_FOUND
VariationNotFoundError	GENERAL
ValidationError	INVALID_CONTEXT
DataError	GENERAL

Errors never throw from the provider. They are returned as part of ResolutionDetails with the defaultValue.

Resolution reasons

The provider maps showwhat results to OpenFeature resolution reasons:

Scenario	Reason
Variation matched via conditions	TARGETING_MATCH
Variation matched with no conditions	STATIC
Flag not found or inactive	ERROR
Type mismatch	ERROR

Lifecycle

• initialize() calls data.load() if the data source implements it.
• onClose() calls data.close() if the data source implements it.

Data sources

Any DefinitionReader works:

Source	Package	Description
MemoryData	showwhat	In-memory definitions (tests, embeds)
Custom	-	Implement DefinitionReader (examples)

Exports

Export	Description
ShowwhatProvider	OpenFeature Provider implementation
ShowwhatProviderOptions	Options type for the provider constructor (data, evaluators, deps)
toShowwhatContext	Utility to flatten EvaluationContext into showwhat Context