Go SDK

Complete reference for the l402-kit Go SDK � net/http middleware for Bitcoin Lightning pay-per-call APIs.

Installation

go get github.com/shinydapps/l402-kit/go@v1.10.0

Requirements: Go 1.21+

---

Quickstart

package main

import (
    "encoding/json"
    "net/http"
    "os"

    l402 "github.com/shinydapps/l402-kit/go"
)

func main() {
    lightning := l402.NewBlinkProvider(
        os.Getenv("BLINK_API_KEY"),
        os.Getenv("BLINK_WALLET_ID"),
    )

    mux := http.NewServeMux()
    mux.Handle("/api/data", l402.Middleware(l402.Options{
        PriceSats: 10,
        Lightning: lightning,
    }, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "application/json")
        json.NewEncoder(w).Encode(map[string]string{"data": "premium content"})
    })))

    http.ListenAndServe(":8080", mux)
}

Get Blink credentials free at dashboard.blink.sv. Payments go directly to your wallet.

---

Self-hosted mode (bring your own provider)

import l402 "github.com/shinydapps/l402-kit/go"

type MyProvider struct{}

func (p *MyProvider) CreateInvoice(ctx context.Context, amountSats int) (l402.Invoice, error) {
    // create invoice with your Lightning node
    // return l402.Invoice{PaymentRequest: "lnbc...", PaymentHash: "...", Macaroon: "..."}
}

mux.Handle("/api/data", l402.Middleware(l402.Options{
    PriceSats: 10,
    Lightning: &MyProvider{},
}, handler))

---

l402.Options

Field	Type	Default	Description
PriceSats	int	required	Price per call in satoshis
Lightning	LightningProvider	required	Your Lightning backend (use NewBlinkProvider)
OnPayment	func(L402Token, int)	�	Callback fired after each verified payment

---

l402.Middleware(opts Options, next http.Handler) http.Handler

Returns an http.Handler compatible with net/http, Chi, Gorilla Mux, and any standard Go HTTP framework.

Behavior

Request	Response
No Authorization header	402 + WWW-Authenticate: L402 macaroon="...", invoice="lnbc..."
Valid L402 <macaroon>:<preimage>	next.ServeHTTP(w, r)
Invalid or expired token	401 Unauthorized
Replayed preimage	401 Token already used

402 response body

{
  "error": "Payment Required",
  "invoice": "lnbc100n1...",
  "macaroon": "eyJoYXNoIjoiYWJjMTIzIiwiZXhwIjoxNzAwMDAwMDAwfQ==",
  "price_sats": 10
}

---

LightningProvider interface

type LightningProvider interface {
    CreateInvoice(ctx context.Context, amountSats int) (Invoice, error)
}

---

OnPayment callback

lightning := l402.NewBlinkProvider(os.Getenv("BLINK_API_KEY"), os.Getenv("BLINK_WALLET_ID"))

mux.Handle("/api/data", l402.Middleware(l402.Options{
    PriceSats: 10,
    Lightning: lightning,
    OnPayment: func(token l402.L402Token, amountSats int) {
        log.Printf("payment: %d sats, preimage: %s", amountSats, token.Preimage)
    },
}, handler))

---

Verification

SHA256(preimage) == paymentHash is verified locally in memory � sub-millisecond, no network call on the hot path. Token expiry (exp field in the macaroon) is checked in the same operation.

The replay guard uses an in-memory map by default (safe for a single process). For multi-instance deployments, use a shared store (Redis or similar) � which adds a 5�50 ms round-trip per verified request.

---

Chi router example

l402.Middleware returns a standard http.Handler, so it works directly with Chi’s r.Handle:

import (
    "github.com/go-chi/chi/v5"
    l402 "github.com/shinydapps/l402-kit/go"
)

r := chi.NewRouter()
lightning := l402.NewBlinkProvider(os.Getenv("BLINK_API_KEY"), os.Getenv("BLINK_WALLET_ID"))

r.Handle("/api/data", l402.Middleware(l402.Options{
    PriceSats: 10,
    Lightning: lightning,
}, http.HandlerFunc(handler)))

---

Error codes

Status	Meaning
402	No payment token � pay the invoice
401	Invalid token or expired macaroon
401	Replayed token (preimage already used)

---

Running

go run main.go

# Test � triggers 402
curl http://localhost:8080/api/data

# Pay invoice, then:
curl -H "Authorization: L402 <macaroon>:<preimage>" http://localhost:8080/api/data