features - Go Feature Flags Service

A feature flag evaluation service for Go with rule-based targeting and multi-tenant support.

Features

• Rule-Based Targeting - Evaluate flags based on user attributes, tenant, and custom conditions
• Multiple Value Types - Boolean, string, and number flag values
• Condition Operators - Equals, not equals, in, not in, exists, starts with
• Multi-Tenant - Built-in support for tenant and user context
• HTTP API - RESTful API with OpenAPI documentation via Huma

Quick Start

go run ./cmd/server --port 8080

Create a Flag

curl -X POST http://localhost:8080/flags \
  -H "Content-Type: application/json" \
  -d '{
    "key": "dark-mode",
    "type": "bool",
    "enabled": true,
    "defaultValue": {"kind": "bool", "bool": false},
    "rules": [
      {
        "id": "beta-testers",
        "conditions": [{"attr": "plan", "op": "eq", "value": "premium"}],
        "value": {"kind": "bool", "bool": true}
      }
    ]
  }'

Evaluate a Flag

curl -X POST http://localhost:8080/flags/dark-mode/evaluate \
  -H "Content-Type: application/json" \
  -d '{
    "tenantId": "acme-corp",
    "userId": "user-123",
    "attrs": {"plan": "premium"}
  }'

API Endpoints

Method	Path	Description
POST	/flags	Create a feature flag
POST	/flags/{key}/evaluate	Evaluate a flag

Condition Operators

Operator	Description
eq	Attribute equals value
neq	Attribute does not equal value
in	Attribute is in list of values
not_in	Attribute is not in list of values
exists	Attribute exists (is not nil)
starts_with	String attribute starts with prefix

Evaluation Order

1. Disabled Check - If flag is disabled, return default value with disabled reason
2. Rule Matching - Evaluate rules in order, first match wins
3. Default - If no rules match, return default value

Development

# Run tests
go test ./...

# Run tests with coverage
go test ./... -coverprofile=coverage.out

# Run linter
golangci-lint run

# Start the server
go run ./cmd/server

License

MIT License - see LICENSE for details.