sdk: cached zap provider queries.

sdk/system.go

@@ -40,6 +40,7 @@ type System struct {
 	RelaySetsCache        cache.Cache32[GenericSets[string, RelayURL]]
 	FollowSetsCache       cache.Cache32[GenericSets[nostr.PubKey, ProfileRef]]
 	TopicSetsCache        cache.Cache32[GenericSets[string, Topic]]
+	ZapProviderCache      cache.Cache32[nostr.PubKey]
 	Hints                 hints.HintsDB
 	Pool                  *nostr.Pool
 	RelayListRelays       *RelayStream
@@ -131,6 +132,9 @@ func NewSystem() *System {
 	if sys.RelayListCache == nil {
 		sys.RelayListCache = cache_memory.New[GenericList[string, Relay]](8000)
 	}
+	if sys.ZapProviderCache == nil {
+		sys.ZapProviderCache = cache_memory.New[nostr.PubKey](8000)
+	}
 
 	if sys.Store == nil {
 		sys.Store = &nullstore.NullStore{}

sdk/zap.go

@@ -0,0 +1,49 @@
+package sdk
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+
+	"fiatjaf.com/nostr"
+	"github.com/tidwall/gjson"
+)
+
+// FetchZapProvider fetches the zap provider public key for a given user from their profile metadata.
+// It uses a cache to avoid repeated fetches. If no zap provider is set in the profile, returns an empty PubKey.
+func (sys *System) FetchZapProvider(ctx context.Context, pk nostr.PubKey) nostr.PubKey {
+	if v, ok := sys.ZapProviderCache.Get(pk); ok {
+		return v
+	}
+
+	pm := sys.FetchProfileMetadata(ctx, pk)
+
+	if pm.LUD16 != "" {
+		parts := strings.Split(pm.LUD16, "@")
+		if len(parts) == 2 {
+			url := "http://" + parts[1] + "/.well-known/lnurlp/" + parts[0]
+			req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+			if err == nil {
+				client := &http.Client{Timeout: 10 * time.Second}
+				resp, err := client.Do(req)
+				if err == nil {
+					defer resp.Body.Close()
+					if body, err := io.ReadAll(resp.Body); err == nil {
+						gj := gjson.ParseBytes(body)
+						if gj.Get("allowsNostr").Type == gjson.True {
+							if pk, err := nostr.PubKeyFromHex(gj.Get("nostrPubkey").Str); err == nil {
+								sys.ZapProviderCache.SetWithTTL(pk, pk, time.Hour*6)
+								return pk
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+
+	sys.ZapProviderCache.SetWithTTL(pk, nostr.ZeroPK, time.Hour*2)
+	return nostr.ZeroPK
+}

sdk/zap_test.go

@@ -0,0 +1,22 @@
+package sdk
+
+import (
+	"context"
+	"testing"
+
+	"fiatjaf.com/nostr"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFetchZapProvider(t *testing.T) {
+	sys := NewSystem()
+	ctx := context.Background()
+
+	pk, err := nostr.PubKeyFromHex("fa984bd7dbb282f07e16e7ae87b26a2a7b9b90b7246a44771f0cf5ae58018f52")
+	require.NoError(t, err)
+
+	zp := sys.FetchZapProvider(ctx, pk)
+	expected, err := nostr.PubKeyFromHex("f81611363554b64306467234d7396ec88455707633f54738f6c4683535098cd3")
+	require.NoError(t, err)
+	require.Equal(t, expected, zp)
+}