Merge pull request #174 from SiaFoundation/nate/fix-budget-panic

Fix budget panic

host/accounts/budget.go

@@ -83,7 +83,7 @@ func (b *Budget) Spend(usage Usage) error {
 	newUsage := b.usage.Add(usage)
 	spent := newUsage.Total()
 	if b.max.Cmp(spent) < 0 {
-		return fmt.Errorf("unable to spend %v, %v remaining: %w", usage.Total(), b.max.Sub(spent), ErrInsufficientFunds)
+		return fmt.Errorf("unable to spend %v, %v remaining: %w", usage.Total(), b.max.Sub(b.usage.Total()), ErrInsufficientFunds)
 	}
 	b.usage = newUsage
 	return nil

host/accounts/budget_test.go

@@ -1,6 +1,7 @@
 package accounts_test
 
 import (
+	"errors"
 	"math"
 	"path/filepath"
 	"reflect"
@@ -184,6 +185,11 @@ func TestBudget(t *testing.T) {
 	}
 	defer budget.Rollback()
 
+	// try to spend more than the budget
+	if err := budget.Spend(accounts.Usage{RPCRevenue: budgetAmount.Mul64(2)}); !errors.Is(err, accounts.ErrInsufficientFunds) {
+		t.Fatal("expected insufficient funds error, got", err)
+	}
+
 	// check that the in-memory state is consistent
 	expectedBalance = expectedBalance.Sub(budgetAmount)
 	balance, err := am.Balance(accountID)