go/consensus/api/transaction: Implement PrettyPrinter interface for Fee

Use it in Transaction's PrettyPrinter to print a transaction's fee.

.changelog/3151.feature.md

@@ -0,0 +1 @@
+go/consensus/api/transaction: Pretty-print transaction's fee amount in tokens

.changelog/3167.feature.2.md

@@ -0,0 +1 @@
+go/consensus/api/transaction: Implement `PrettyPrinter` interface for `Fee`

go/consensus/api/transaction/gas.go

@@ -1,8 +1,15 @@
 package transaction
 
 import (
+	"context"
+	"fmt"
+	"io"
+
 	"github.com/oasisprotocol/oasis-core/go/common/errors"
+	"github.com/oasisprotocol/oasis-core/go/common/prettyprint"
 	"github.com/oasisprotocol/oasis-core/go/common/quantity"
+
+	"github.com/oasisprotocol/oasis-core/go/staking/api/token"
 )
 
 var (
@@ -12,6 +19,8 @@ var (
 
 	// ErrGasPriceTooLow is the error returned when the gas price is too low.
 	ErrGasPriceTooLow = errors.New(moduleName, 3, "transaction: gas price too low")
+
+	_ prettyprint.PrettyPrinter = (*Fee)(nil)
 )
 
 // Gas is the consensus gas representation.
@@ -26,6 +35,25 @@ type Fee struct {
 	Gas Gas `json:"gas"`
 }
 
+// PrettyPrint writes a pretty-printed representation of the fee to the given
+// writer.
+func (f Fee) PrettyPrint(ctx context.Context, prefix string, w io.Writer) {
+	fmt.Fprintf(w, "%sAmount: ", prefix)
+	token.PrettyPrintAmount(ctx, f.Amount, w)
+	fmt.Fprintln(w)
+
+	fmt.Fprintf(w, "%sGas limit: %d\n", prefix, f.Gas)
+	fmt.Fprintf(w, "%s(gas price: ", prefix)
+	token.PrettyPrintAmount(ctx, *f.GasPrice(), w)
+	fmt.Fprintln(w, " per gas unit)")
+}
+
+// PrettyType returns a representation of Fee that can be used for pretty
+// printing.
+func (f Fee) PrettyType() (interface{}, error) {
+	return f, nil
+}
+
 // GasPrice returns the gas price implied by the amount and gas.
 func (f Fee) GasPrice() *quantity.Quantity {
 	if f.Amount.IsZero() || f.Gas == 0 {

go/consensus/api/transaction/transaction.go

@@ -83,7 +83,8 @@ func (t Transaction) PrettyPrintBody(ctx context.Context, prefix string, w io.Wr
 func (t Transaction) PrettyPrint(ctx context.Context, prefix string, w io.Writer) {
 	fmt.Fprintf(w, "%sNonce:  %d\n", prefix, t.Nonce)
 	if t.Fee != nil {
-		fmt.Fprintf(w, "%sFee:    %s (gas limit: %d, gas price: %s)\n", prefix, t.Fee.Amount, t.Fee.Gas, t.Fee.GasPrice())
+		fmt.Fprintf(w, "%sFee:\n", prefix)
+		t.Fee.PrettyPrint(ctx, prefix+"  ", w)
 	} else {
 		fmt.Fprintf(w, "%sFee:   none\n", prefix)
 	}