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Go SDK

github.com/feathq/go-sdk is the Go SDK. Standard library only, no third-party dependencies. Evaluates flags locally against a polled datafile.

Install

go get github.com/feathq/go-sdk

Go 1.23 or newer.

import "github.com/feathq/go-sdk/feat"

Usage

package main

import (
    "context"
    "fmt"
    "os"

    "github.com/feathq/go-sdk/feat"
)

func main() {
    client, err := feat.NewClient(feat.Config{
        APIKey:       os.Getenv("FEAT_SERVER_KEY"),
        DataPlaneURL: "https://data.feat.so",
    })
    if err != nil {
        panic(err)
    }
    defer client.Close()

    client.Start(context.Background())
    if err := client.Ready(context.Background()); err != nil {
        panic(err)
    }

    evalCtx := feat.EvalContext{
        TargetingKey: "user-123",
        Kinds: map[string]feat.ContextKindObject{
            "user": {Key: "user-123", Attrs: map[string]any{
                "plan":  "pro",
                "email": "alice@example.com",
            }},
        },
    }

    fmt.Println("checkout-v2:", client.GetBooleanValue("checkout-v2", false, evalCtx))
}

Use a server key (feat_sdk_…).

API

enabled := client.GetBooleanValue("checkout-v2", false, evalCtx)
variant := client.GetStringValue("hero-copy", "control", evalCtx)
limit   := client.GetNumberValue("rate-limit", 100.0, evalCtx)
config  := client.GetObjectValue("layout-config", defaultMap, evalCtx)

result := client.Evaluate("checkout-v2", false, evalCtx)
// result.Value, result.VariationID, result.Reason, result.ErrorMessage

Reason is one of TARGETING_MATCH, SPLIT, FALLTHROUGH, DEFAULT, DISABLED, ERROR. See Evaluation order.

Lifecycle

NewClient constructs but does not start polling.
Start(ctx) spawns the polling goroutine. The goroutine runs until Close() is called or ctx is cancelled.
Ready(ctx) blocks until the first datafile arrives or the context cancels.
The in-memory datafile is held in an atomic.Pointer for lock-free reads.

Configuration

feat.Config{
    APIKey:       os.Getenv("FEAT_SERVER_KEY"),
    DataPlaneURL: "https://data.feat.so",
    PollInterval: 30 * time.Second,   // default 30s, minimum 5s
    Bootstrap:    serializedDatafile, // optional: skip the initial fetch
}

Semantics

The Go SDK ports the same evaluation algorithm as @feathq/feat-eval bit-for-bit. The same datafile, the same context, and the same flag key always give the same result across Node.js, Go, Python, and Ruby.