From ffb6504f674d855f0047ef16e495f2c9b5457ffb Mon Sep 17 00:00:00 2001
From: Evgeniy Stratonikov <evgeniy@nspcc.ru>
Date: Mon, 27 Dec 2021 14:40:42 +0300
Subject: [PATCH] vm: cut trailing spaces in `PrintOps`

When there is a single big instruction (like PUSHDATA4) in script,
all other instructions are padded to the right with spaces.
This makes it hard to view script in terminal, because long lines
are usually wrapped at the screen boundary and printed as multiple lines.

The culprit is our `cursor` field which is printed in the last column
and causes all previous fields to have the same length for every
instruction. One way to fix this is to omit cursor field if it is empty.

Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>
---
 pkg/vm/vm.go      |  8 ++++----
 pkg/vm/vm_test.go | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 5cc6b872a..52e1d7f79 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -145,7 +145,7 @@ func (v *VM) PrintOps(out io.Writer) {
 		out = os.Stdout
 	}
 	w := tabwriter.NewWriter(out, 0, 0, 4, ' ', 0)
-	fmt.Fprintln(w, "INDEX\tOPCODE\tPARAMETER\t")
+	fmt.Fprintln(w, "INDEX\tOPCODE\tPARAMETER")
 	realctx := v.Context()
 	ctx := realctx.Copy()
 	ctx.ip = 0
@@ -154,10 +154,10 @@ func (v *VM) PrintOps(out io.Writer) {
 		cursor := ""
 		instr, parameter, err := ctx.Next()
 		if ctx.ip == realctx.ip {
-			cursor = "<<"
+			cursor = "\t<<"
 		}
 		if err != nil {
-			fmt.Fprintf(w, "%d\t%s\tERROR: %s\t%s\n", ctx.ip, instr, err, cursor)
+			fmt.Fprintf(w, "%d\t%s\tERROR: %s%s\n", ctx.ip, instr, err, cursor)
 			break
 		}
 		var desc = ""
@@ -203,7 +203,7 @@ func (v *VM) PrintOps(out io.Writer) {
 			}
 		}
 
-		fmt.Fprintf(w, "%d\t%s\t%s\t%s\n", ctx.ip, instr, desc, cursor)
+		fmt.Fprintf(w, "%d\t%s\t%s%s\n", ctx.ip, instr, desc, cursor)
 		if ctx.nextip >= len(ctx.prog) {
 			break
 		}
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index df1b7b279..213a28b6a 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -9,6 +9,7 @@ import (
 	"math"
 	"math/big"
 	"math/rand"
+	"strings"
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/internal/random"
@@ -1181,6 +1182,25 @@ func TestPICKITEM(t *testing.T) {
 	})
 }
 
+func TestVMPrintOps(t *testing.T) {
+	w := io.NewBufBinWriter()
+	emit.Bytes(w.BinWriter, make([]byte, 1000))
+	emit.Opcodes(w.BinWriter, opcode.PUSH0)
+	emit.Bytes(w.BinWriter, make([]byte, 8))
+
+	buf := bytes.NewBuffer(nil)
+	v := New()
+	v.Load(w.Bytes())
+	v.PrintOps(buf)
+
+	ss := strings.Split(buf.String(), "\n")
+	require.Equal(t, 5, len(ss)) // header + 3 opcodes + trailing newline
+	require.True(t, len(ss[0]) < 1000)
+	require.True(t, len(ss[1]) > 1000)
+	require.True(t, len(ss[2]) < 1000)
+	require.True(t, len(ss[3]) < 1000)
+}
+
 func TestPICKITEMDupArray(t *testing.T) {
 	prog := makeProgram(opcode.DUP, opcode.PUSH0, opcode.PICKITEM, opcode.ABS)
 	vm := load(prog)