flagbearer for Go

The Go SDK for Flagbearer. Requires Go 1.23 or later.

Install

go get github.com/flagbearer-dev/sdks/go

import flagbearer "github.com/flagbearer-dev/sdks/go"

Keys

Use a server key, which starts with fbs_. Server keys are secret: read them from the environment, such as FLAGBEARER_SERVER_KEY, and never put them in browser code or in the repository. Browsers use client keys, which start with fbc_, through @flagbearer/web.

Sync at startup

Create one client per process, when the app starts, and wait for it to sync before accepting requests:

flags, err := flagbearer.New(os.Getenv("FLAGBEARER_SERVER_KEY"))
if err != nil {
	log.Fatal(err) // An empty key or an invalid URL.
}

ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
if err := flags.Sync(ctx); err != nil {
	// Keep starting: checks use their defaults, and the SDK retries in the background.
	log.Printf("Initial Flagbearer sync failed: %v", err)
}

Check per request

Pass each request's user explicitly, and a default:

func search(w http.ResponseWriter, r *http.Request) {
	user := flagbearer.User{Key: currentUser(r).ID, Email: currentUser(r).Email}
	advanced := flags.IsEnabled("advanced-search", user, false)
	// …
}

The email is optional. Include it to turn flags on for testers by email. The default is used until the client has synced, and when the flag doesn't exist.

Shut down

Keep the client for the life of the process, not per request. Close it on shutdown:

defer flags.Close()

Serverless functions should call flags.Flush(ctx) at the end of each invocation.