multi: move label validation to rpc and simplify validation function

Previously labels with reserved prefixes were added to provide us
with a way to identify automatically dispatched loops. This commit moves
the validation of these labels to the rpc level so that it will only
apply to user-initiated swaps.

labels/labels.go

@@ -2,6 +2,7 @@ package labels
 
 import (
 	"errors"
+	"strings"
 )
 
 const (
@@ -29,16 +30,10 @@ func Validate(label string) error {
 		return ErrLabelTooLong
 	}
 
-	// If the label is shorter than our reserved prefix, it cannot contain
-	// it.
-	if len(label) < len(Reserved) {
-		return nil
-	}
-
 	// Check if our label begins with our reserved prefix. We don't mind if
 	// it has our reserved prefix in another case, we just need to be able
 	// to reserve a subset of labels with this prefix.
-	if label[0:len(Reserved)] == Reserved {
+	if strings.HasPrefix(label, Reserved) {
 		return ErrReservedPrefix
 	}
 

loopd/swapclient_server.go

@@ -11,6 +11,7 @@ import (
 	"github.com/btcsuite/btcutil"
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/loop"
+	"github.com/lightninglabs/loop/labels"
 	"github.com/lightninglabs/loop/liquidity"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/looprpc"
@@ -79,6 +80,11 @@ func (s *swapClientServer) LoopOut(ctx context.Context,
 		}
 	}
 
+	// Check that the label is valid.
+	if err := labels.Validate(in.Label); err != nil {
+		return nil, err
+	}
+
 	req := &loop.OutRequest{
 		Amount:              btcutil.Amount(in.Amt),
 		DestAddr:            sweepAddr,
@@ -477,6 +483,11 @@ func (s *swapClientServer) LoopIn(ctx context.Context,
 		return nil, err
 	}
 
+	// Check that the label is valid.
+	if err := labels.Validate(in.Label); err != nil {
+		return nil, err
+	}
+
 	req := &loop.LoopInRequest{
 		Amount:         btcutil.Amount(in.Amt),
 		MaxMinerFee:    btcutil.Amount(in.MaxMinerFee),

loopdb/loopin.go

@@ -125,8 +125,9 @@ func putLabel(bucket *bbolt.Bucket, label string) error {
 		return nil
 	}
 
-	if err := labels.Validate(label); err != nil {
+	// Check that the label does not exceed our maximum length.
-		return err
+	if len(label) > labels.MaxLength {
+		return labels.ErrLabelTooLong
 	}
 
 	return bucket.Put(labelKey, []byte(label))

loopin.go

@@ -14,7 +14,6 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightninglabs/lndclient"
-	"github.com/lightninglabs/loop/labels"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightningnetwork/lnd/chainntnfs"
@@ -79,11 +78,6 @@ func newLoopInSwap(globalCtx context.Context, cfg *swapConfig,
 	currentHeight int32, request *LoopInRequest) (*loopInInitResult,
 	error) {
 
-	// Before we start, check that the label is valid.
-	if err := labels.Validate(request.Label); err != nil {
-		return nil, err
-	}
-
 	// Request current server loop in terms and use these to calculate the
 	// swap fee that we should subtract from the swap amount in the payment
 	// request that we send to the server.

loopout.go

@@ -13,7 +13,6 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/lightninglabs/lndclient"
-	"github.com/lightninglabs/loop/labels"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/sweep"
@@ -88,11 +87,6 @@ type loopOutInitResult struct {
 func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 	currentHeight int32, request *OutRequest) (*loopOutInitResult, error) {
 
-	// Before we start, check that the label is valid.
-	if err := labels.Validate(request.Label); err != nil {
-		return nil, err
-	}
-
 	// Generate random preimage.
 	var swapPreimage [32]byte
 	if _, err := rand.Read(swapPreimage[:]); err != nil {