nip60: just rely on nut08 overpaid fees to get change when melting, don't try to swap beforehand.

nip60/helpers.go

@@ -115,16 +115,12 @@ func signOutput(
 
 // constructProofs unblinds the blindedSignatures and returns the proofs
 func constructProofs(
+	prep preparedOutputs,
 	blindedSignatures cashu.BlindedSignatures,
-	blindedMessages cashu.BlindedMessages,
-	secrets []string,
-	rs []*secp256k1.PrivateKey,
 	keys map[uint64]*btcec.PublicKey,
 ) (cashu.Proofs, error) {
-	sigsLenght := len(blindedSignatures)
+	// blinded sigs might be less than slices in prep, but that is fine, we just ignore the last
-	if sigsLenght != len(secrets) || sigsLenght != len(rs) {
+	// items in prep. it happens when we are building proofs from change sent by a mint after melt.
-		return nil, errors.New("lengths do not match")
-	}
 
 	proofs := make(cashu.Proofs, len(blindedSignatures))
 	for i, blindedSignature := range blindedSignatures {
@@ -139,7 +135,7 @@ func constructProofs(
 			if !nut12.VerifyBlindSignatureDLEQ(
 				*blindedSignature.DLEQ,
 				pubkey,
-				blindedMessages[i].B_,
+				prep.bm[i].B_,
 				blindedSignature.C_,
 			) {
 				return nil, errors.New("got blinded signature with invalid DLEQ proof")
@@ -147,19 +143,19 @@ func constructProofs(
 				dleq = &cashu.DLEQProof{
 					E: blindedSignature.DLEQ.E,
 					S: blindedSignature.DLEQ.S,
-					R: hex.EncodeToString(rs[i].Serialize()),
+					R: hex.EncodeToString(prep.rs[i].Serialize()),
 				}
 			}
 		}
 
-		C, err := unblindSignature(blindedSignature.C_, rs[i], pubkey)
+		C, err := unblindSignature(blindedSignature.C_, prep.rs[i], pubkey)
 		if err != nil {
 			return nil, err
 		}
 
 		proof := cashu.Proof{
 			Amount: blindedSignature.Amount,
-			Secret: secrets[i],
+			Secret: prep.secrets[i],
 			C:      C,
 			Id:     blindedSignature.Id,
 			DLEQ:   dleq,

nip60/lightning-swap.go

@@ -139,7 +139,11 @@ inspectmeltstatusresponse:
 		return nil, fmt.Errorf("mint request to %s failed (%s): %w", to, mintQuote, err), manualActionRequired
 	}
 
-	proofs, err = constructProofs(mintResponse.Signatures, blindedMessages, secrets, rs, keysetKeys)
+	proofs, err = constructProofs(preparedOutputs{
+		bm:      blindedMessages,
+		secrets: secrets,
+		rs:      rs,
+	}, mintResponse.Signatures, keysetKeys)
 	if err != nil {
 		return nil, fmt.Errorf("error constructing proofs: %w", err), manualActionRequired
 	}

nip60/pay.go

@@ -26,18 +26,27 @@ func (w *Wallet) PayBolt11(ctx context.Context, invoice string, opts ...SendOpti
 
 	var chosen chosenTokens
 	var meltQuote string
-	var meltAmount uint64
+	var meltAmountWithoutFeeReserve uint64
 
 	feeReservePct := uint64(1)
 	feeReserveAbs := uint64(1)
+
+	excludeMints := make([]string, 0, 1)
+
 	for range 10 {
 		amount := invoiceAmount*(100+feeReservePct)/100 + feeReserveAbs
 		var fee uint64
-		chosen, fee, err = w.getProofsForSending(ctx, amount, ss.specificMint)
+		chosen, fee, err = w.getProofsForSending(ctx, amount, ss.specificMint, excludeMints)
 		if err != nil {
 			return "", err
 		}
 
+		// we will only do this in mints that support nut08
+		if info, _ := client.GetMintInfo(ctx, chosen.mint); info == nil || !info.Nuts.Nut08.Supported {
+			excludeMints = append(excludeMints, chosen.mint)
+			continue
+		}
+
 		// request _melt_ quote (ask the mint how much will it cost to pay a bolt11 invoice)
 		meltResp, err := client.PostMeltQuoteBolt11(ctx, chosen.mint, nut05.PostMeltQuoteBolt11Request{
 			Request: invoice,
@@ -49,36 +58,45 @@ func (w *Wallet) PayBolt11(ctx context.Context, invoice string, opts ...SendOpti
 
 		// if amount in proofs is not sufficient to pay for the melt request,
 		// increase the amount and get proofs again  (because of lighting fees)
-		meltQuote = meltResp.Quote
+		if meltResp.Amount+meltResp.FeeReserve+fee > chosen.proofs.Amount() {
-		meltAmount = meltResp.Amount + meltResp.FeeReserve + fee
-
-		if meltAmount > chosen.proofs.Amount() {
 			feeReserveAbs++
 		} else {
+			meltQuote = meltResp.Quote
+			meltAmountWithoutFeeReserve = invoiceAmount + fee
 			goto meltworked
 		}
 	}
 
-	return "", fmt.Errorf("stop trying to do the melt because the invoice is too expensive")
+	return "", fmt.Errorf("stopped trying to do the melt because all the mints are charging way too much")
 
 meltworked:
-	// swap our proofs so we get the exact amount for paying the invoice
+	activeKeyset, err := client.GetActiveKeyset(ctx, chosen.mint)
-	principal, change, err := w.SwapProofs(ctx, chosen.mint, chosen.proofs, meltAmount)
 	if err != nil {
-		return "", fmt.Errorf("failed to swap at %s into the exact melt amount: %w", chosen.mint, err)
+		return "", fmt.Errorf("failed to get active keyset for %s: %w", chosen.mint, err)
+	}
+	ksKeys, err := parseKeysetKeys(activeKeyset.Keys)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse keys for %s: %w", chosen.mint, err)
 	}
 
-	if err := w.saveChangeAndDeleteUsedTokens(ctx, chosen.mint, change, chosen.tokenIndexes); err != nil {
+	// since we rely on nut08 we will send all the proofs we've gathered and expect a change
-		return "", err
+	// we do a split here and discard the principal, as we won't get it back from the mint
-	}
+	_, preChange, err := splitIntoPrincipalAndChange(
+		chosen.keysets,
+		chosen.proofs,
+		meltAmountWithoutFeeReserve,
+		activeKeyset.Id,
+		nil,
+	)
 
 	// request from mint to _melt_ into paying the invoice
 	delay := 200 * time.Millisecond
 	// this request will block until the invoice is paid or it fails
 	// (but the API also says it can return "pending" so we handle both)
 	meltStatus, err := client.PostMeltBolt11(ctx, chosen.mint, nut05.PostMeltBolt11Request{
-		Quote:  meltQuote,
+		Quote:   meltQuote,
-		Inputs: principal,
+		Inputs:  chosen.proofs,
+		Outputs: preChange.bm,
 	})
 inspectmeltstatusresponse:
 	if err != nil || meltStatus.State == nut05.Unpaid {
@@ -94,5 +112,15 @@ inspectmeltstatusresponse:
 		}
 	}
 
+	// the invoice has been paid, now we save the change we got
+	change, err := constructProofs(preChange, meltStatus.Change, ksKeys)
+	if err != nil {
+		return "", fmt.Errorf("failed to construct principal proofs: %w", err)
+	}
+
+	if err := w.saveChangeAndDeleteUsedTokens(ctx, chosen.mint, change, chosen.tokenIndexes); err != nil {
+		return "", err
+	}
+
 	return meltStatus.Preimage, nil
 }

nip60/send.go

@@ -59,7 +59,7 @@ func (w *Wallet) SendToken(ctx context.Context, amount uint64, opts ...SendOptio
 	w.tokensMu.Lock()
 	defer w.tokensMu.Unlock()
 
-	chosen, _, err := w.getProofsForSending(ctx, amount, ss.specificMint)
+	chosen, _, err := w.getProofsForSending(ctx, amount, ss.specificMint, nil)
 	if err != nil {
 		return "", err
 	}
@@ -138,7 +138,7 @@ func (w *Wallet) saveChangeAndDeleteUsedTokens(
 				deleteEvent := nostr.Event{
 					CreatedAt: nostr.Now(),
 					Kind:      5,
-					Tags:      nostr.Tags{{"e", token.event.ID}, {"k", "7375"}},
+					Tags:      nostr.Tags{{"e", token.event.ID}, {"k", "7375"}, {"alt", "deleting"}},
 				}
 				w.wl.kr.SignEvent(ctx, &deleteEvent)
 				w.wl.Changes <- deleteEvent
@@ -163,12 +163,16 @@ func (w *Wallet) getProofsForSending(
 	ctx context.Context,
 	amount uint64,
 	specificMint string,
+	excludeMints []string,
 ) (chosenTokens, uint64, error) {
 	byMint := make(map[string]chosenTokens)
 	for t, token := range w.Tokens {
 		if specificMint != "" && token.Mint != specificMint {
 			continue
 		}
+		if slices.Contains(excludeMints, token.Mint) {
+			continue
+		}
 
 		part, ok := byMint[token.Mint]
 		if !ok {

nip60/swap.go

@@ -3,8 +3,11 @@ package nip60
 import (
 	"context"
 	"fmt"
+	"slices"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/elnosh/gonuts/cashu"
+	"github.com/elnosh/gonuts/cashu/nuts/nut02"
 	"github.com/elnosh/gonuts/cashu/nuts/nut03"
 	"github.com/elnosh/gonuts/cashu/nuts/nut10"
 	"github.com/nbd-wtf/go-nostr/nip60/client"
@@ -41,7 +44,6 @@ func (w *Wallet) SwapProofs(
 		opt(&ss)
 	}
 
-	// fetch all this keyset drama first
 	keysets, err := client.GetAllKeysets(ctx, mint)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to get all keysets for %s: %w", mint, err)
@@ -55,6 +57,63 @@ func (w *Wallet) SwapProofs(
 		return nil, nil, fmt.Errorf("failed to parse keys for %s: %w", mint, err)
 	}
 
+	prePrincipal, preChange, err := splitIntoPrincipalAndChange(
+		keysets,
+		proofs,
+		targetAmount,
+		activeKeyset.Id,
+		ss.spendingCondition,
+	)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if ss.mustSignOutputs {
+		for i, output := range prePrincipal.bm {
+			prePrincipal.bm[i].Witness, err = signOutput(w.PrivateKey, output)
+			if err != nil {
+				return nil, nil, fmt.Errorf("failed to sign output message %d: %w", i, err)
+			}
+		}
+	}
+
+	req := nut03.PostSwapRequest{
+		Inputs:  proofs,
+		Outputs: slices.Concat(prePrincipal.bm, preChange.bm),
+	}
+
+	res, err := client.PostSwap(ctx, mint, req)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to swap tokens at %s: %w", mint, err)
+	}
+
+	// build the proofs locally from mint's response
+	principal, err = constructProofs(prePrincipal, res.Signatures[0:len(prePrincipal.bm)], ksKeys)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to construct principal proofs: %w", err)
+	}
+
+	change, err = constructProofs(preChange, res.Signatures[len(prePrincipal.bm):], ksKeys)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to construct principal proofs: %w", err)
+	}
+
+	return principal, change, nil
+}
+
+type preparedOutputs struct {
+	bm      cashu.BlindedMessages
+	rs      []*btcec.PrivateKey
+	secrets []string
+}
+
+func splitIntoPrincipalAndChange(
+	keysets []nut02.Keyset,
+	proofs cashu.Proofs,
+	targetAmount uint64,
+	activeKeysetId string,
+	spendingCondition *nut10.SpendingCondition,
+) (principal preparedOutputs, change preparedOutputs, err error) {
 	// decide the shape of the proofs we'll swap for
 	proofsAmount := proofs.Amount()
 	var (
@@ -71,8 +130,8 @@ func (w *Wallet) SwapProofs(
 		principalAmount = targetAmount - fee
 		changeAmount = 0
 	} else {
-		return nil, nil, fmt.Errorf("can't swap for more than we are sending: %d > %d",
+		err = fmt.Errorf("can't swap for more than we are sending: %d > %d", targetAmount, proofsAmount)
-			targetAmount, proofsAmount)
+		return
 	}
 	splits := make([]uint64, 0, len(proofs)*2)
 	splits = append(splits, cashu.AmountSplit(principalAmount)...)
@@ -80,35 +139,19 @@ func (w *Wallet) SwapProofs(
 	splits = append(splits, cashu.AmountSplit(changeAmount)...)
 
 	// prepare message to send to mint
-	outputs, secrets, rs, err := createBlindedMessages(splits, activeKeyset.Id, ss.spendingCondition)
+	bm, secrets, rs, err := createBlindedMessages(splits, activeKeysetId, spendingCondition)
 	if err != nil {
-		return nil, nil, fmt.Errorf("failed to create blinded message: %w", err)
+		err = fmt.Errorf("failed to create blinded message: %w", err)
+		return
 	}
 
-	if ss.mustSignOutputs {
+	return preparedOutputs{
-		for i, output := range outputs {
+			bm:      bm[0:changeStartIndex],
-			outputs[i].Witness, err = signOutput(w.PrivateKey, output)
+			rs:      rs[0:changeStartIndex],
-			if err != nil {
+			secrets: secrets[0:changeStartIndex],
-				return nil, nil, fmt.Errorf("failed to sign output message %d: %w", i, err)
+		}, preparedOutputs{
-			}
+			bm:      bm[changeStartIndex:],
-		}
+			rs:      rs[changeStartIndex:],
-	}
+			secrets: secrets[changeStartIndex:],
-
+		}, nil
-	req := nut03.PostSwapRequest{
-		Inputs:  proofs,
-		Outputs: outputs,
-	}
-
-	res, err := client.PostSwap(ctx, mint, req)
-	if err != nil {
-		return nil, nil, fmt.Errorf("failed to swap tokens at %s: %w", mint, err)
-	}
-
-	// build the proofs locally from mint's response
-	newProofs, err := constructProofs(res.Signatures, req.Outputs, secrets, rs, ksKeys)
-	if err != nil {
-		return nil, nil, fmt.Errorf("failed to construct proofs: %w", err)
-	}
-
-	return newProofs[0:changeStartIndex], newProofs[changeStartIndex:], nil
 }