liquidity: fail suggest swaps when no rules are set

In an effort to surface more information about why autoloop is not
executing, we add an error when suggest swaps is called with no rules.
In other cases we can surface a reason enum with each rule that is set,
but in the case where we have no rules, there are no results to
accompany with reasons.

cmd/loop/liquidity.go

@@ -2,12 +2,15 @@ package main
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strconv"
 
 	"github.com/lightninglabs/loop/liquidity"
 	"github.com/lightninglabs/loop/looprpc"
 	"github.com/urfave/cli"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 var getLiquidityParamsCommand = cli.Command{
@@ -411,11 +414,22 @@ func suggestSwap(ctx *cli.Context) error {
 	resp, err := client.SuggestSwaps(
 		context.Background(), &looprpc.SuggestSwapsRequest{},
 	)
-	if err != nil {
+	if err == nil {
+		printJSON(resp)
+		return nil
+	}
+
+	// If we got an error because no rules are set, we want to display a
+	// friendly message.
+	rpcErr, ok := status.FromError(err)
+	if !ok {
 		return err
 	}
 
-	printJSON(resp)
+	if rpcErr.Code() != codes.FailedPrecondition {
+		return err
+	}
 
-	return nil
+	return errors.New("no rules set for autolooper, please set rules " +
+		"using the setrule command")
 }

liquidity/liquidity.go

@@ -178,6 +178,9 @@ var (
 	// less than the server minimum.
 	ErrMinLessThanServer = errors.New("minimum swap amount is less than " +
 		"server minimum")
+
+	// ErrNoRules is returned when no rules are set for swap suggestions.
+	ErrNoRules = errors.New("no rules set for autoloop")
 )
 
 // Config contains the external functionality required to run the
@@ -439,7 +442,14 @@ func (m *Manager) Run(ctx context.Context) error {
 	for {
 		select {
 		case <-m.cfg.AutoloopTicker.Ticks():
-			if err := m.autoloop(ctx); err != nil {
+			err := m.autoloop(ctx)
+			switch err {
+			case ErrNoRules:
+				log.Debugf("No rules configured for autoloop")
+
+			case nil:
+
+			default:
 				log.Errorf("autoloop failed: %v", err)
 			}
 
@@ -562,7 +572,7 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 	// If we have no rules set, exit early to avoid unnecessary calls to
 	// lnd and the server.
 	if len(m.params.ChannelRules) == 0 {
-		return nil, nil
+		return nil, ErrNoRules
 	}
 
 	// If our start date is in the future, we interpret this as meaning that

liquidity/liquidity_test.go

@@ -496,10 +496,12 @@ func TestSuggestSwaps(t *testing.T) {
 		name  string
 		rules map[lnwire.ShortChannelID]*ThresholdRule
 		swaps []loop.OutRequest
+		err   error
 	}{
 		{
 			name:  "no rules",
 			rules: map[lnwire.ShortChannelID]*ThresholdRule{},
+			err:   ErrNoRules,
 		},
 		{
 			name: "loop out",
@@ -534,7 +536,7 @@ func TestSuggestSwaps(t *testing.T) {
 
 			testSuggestSwaps(
 				t, newSuggestSwapsSetup(cfg, lnd, params),
-				testCase.swaps, nil,
+				testCase.swaps, testCase.err,
 			)
 		})
 	}

loopd/swapclient_server.go

@@ -21,6 +21,8 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/queue"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 const (
@@ -703,7 +705,13 @@ func (s *swapClientServer) SuggestSwaps(ctx context.Context,
 	_ *looprpc.SuggestSwapsRequest) (*looprpc.SuggestSwapsResponse, error) {
 
 	swaps, err := s.liquidityMgr.SuggestSwaps(ctx, false)
-	if err != nil {
+	switch err {
+	case liquidity.ErrNoRules:
+		return nil, status.Error(codes.FailedPrecondition, err.Error())
+
+	case nil:
+
+	default:
 		return nil, err
 	}
 

release_notes.md

@@ -31,5 +31,8 @@ This file tracks release notes for the loop client.
   been renamed to `Autoloop`, `AutoloopBudgetSat` and `AutoloopBudgetStartSec`. 
 * The `autoout` flag for enabling automatic dispatch of loop out swaps has been
   renamed to `autoloop` so that it can cover loop out and loop in.
+* The `SuggestSwaps` rpc call will now fail with a `FailedPrecondition` grpc
+  error code if no rules are configured for the autolooper. Previously the rpc
+  would return an empty response.
 
 #### Bug Fixes