sdk: cached mint keys queries.

sdk/system.go

@@ -14,6 +14,7 @@ import (
 	"fiatjaf.com/nostr/sdk/hints/memoryh"
 	"fiatjaf.com/nostr/sdk/kvstore"
 	kvstore_memory "fiatjaf.com/nostr/sdk/kvstore/memory"
+	"github.com/btcsuite/btcd/btcec/v2"
 )
 
 // System represents the core functionality of the SDK, providing access to
@@ -41,6 +42,7 @@ type System struct {
 	FollowSetsCache       cache.Cache32[GenericSets[nostr.PubKey, ProfileRef]]
 	TopicSetsCache        cache.Cache32[GenericSets[string, Topic]]
 	ZapProviderCache      cache.Cache32[nostr.PubKey]
+	MintKeysCache         cache.Cache32[map[uint64]*btcec.PublicKey]
 	Hints                 hints.HintsDB
 	Pool                  *nostr.Pool
 	RelayListRelays       *RelayStream
@@ -135,6 +137,9 @@ func NewSystem() *System {
 	if sys.ZapProviderCache == nil {
 		sys.ZapProviderCache = cache_memory.New[nostr.PubKey](8000)
 	}
+	if sys.MintKeysCache == nil {
+		sys.MintKeysCache = cache_memory.New[map[uint64]*btcec.PublicKey](8000)
+	}
 
 	if sys.Store == nil {
 		sys.Store = &nullstore.NullStore{}

sdk/zap.go

@@ -2,12 +2,16 @@ package sdk
 
 import (
 	"context"
+	"crypto/sha256"
 	"io"
 	"net/http"
 	"strings"
 	"time"
 
 	"fiatjaf.com/nostr"
+	"fiatjaf.com/nostr/nip60"
+	"fiatjaf.com/nostr/nip60/client"
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/tidwall/gjson"
 )
 
@@ -47,3 +51,25 @@ func (sys *System) FetchZapProvider(ctx context.Context, pk nostr.PubKey) nostr.
 	sys.ZapProviderCache.SetWithTTL(pk, nostr.ZeroPK, time.Hour*2)
 	return nostr.ZeroPK
 }
+
+// FetchMintKeys fetches the active keyset from the given mint URL and parses the keys.
+// It uses a cache to avoid repeated fetches.
+func (sys *System) FetchMintKeys(ctx context.Context, mintURL string) (map[uint64]*btcec.PublicKey, error) {
+	hash := sha256.Sum256([]byte(mintURL))
+	if v, ok := sys.MintKeysCache.Get(hash); ok {
+		return v, nil
+	}
+
+	keyset, err := client.GetActiveKeyset(ctx, mintURL)
+	if err != nil {
+		return nil, err
+	}
+
+	ksKeys, err := nip60.ParseKeysetKeys(keyset.Keys)
+	if err != nil {
+		return nil, err
+	}
+
+	sys.MintKeysCache.SetWithTTL(hash, ksKeys, time.Hour*6)
+	return ksKeys, nil
+}