vm: use new Context.Next() to properly dump programs

Fix #295, deduplicate code and add `inspect` parameter to the vm command to
dump AVMs (`contract inspect` works with Go code).

cli/vm/vm.go

@@ -1,6 +1,10 @@
 package vm
 
 import (
+	"errors"
+	"io/ioutil"
+
+	"github.com/CityOfZion/neo-go/pkg/vm"
 	vmcli "github.com/CityOfZion/neo-go/pkg/vm/cli"
 	"github.com/urfave/cli"
 )
@@ -14,6 +18,19 @@ func NewCommand() cli.Command {
 		Flags: []cli.Flag{
 			cli.BoolFlag{Name: "debug, d"},
 		},
+		Subcommands: []cli.Command{
+			{
+				Name:   "inspect",
+				Usage:  "dump instructions of the avm file given",
+				Action: inspect,
+				Flags: []cli.Flag{
+					cli.StringFlag{
+						Name:  "in, i",
+						Usage: "input file of the program (AVM)",
+					},
+				},
+			},
+		},
 	}
 }
 
@@ -21,3 +38,18 @@ func startVMPrompt(ctx *cli.Context) error {
 	p := vmcli.New()
 	return p.Run()
 }
+
+func inspect(ctx *cli.Context) error {
+	avm := ctx.String("in")
+	if len(avm) == 0 {
+		return cli.NewExitError(errors.New("no input file given"), 1)
+	}
+	b, err := ioutil.ReadFile(avm)
+	if err != nil {
+		return cli.NewExitError(err, 1)
+	}
+	v := vm.New(0)
+	v.LoadScript(b)
+	v.PrintOps()
+	return nil
+}

pkg/vm/compiler/compiler.go

@@ -13,7 +13,6 @@ import (
 	"log"
 	"os"
 	"strings"
-	"text/tabwriter"
 
 	"github.com/CityOfZion/neo-go/pkg/vm"
 	"golang.org/x/tools/go/loader"
@@ -108,25 +107,9 @@ func CompileAndInspect(src string) error {
 		return err
 	}
 
-	w := tabwriter.NewWriter(os.Stdout, 0, 0, 4, ' ', 0)
-	fmt.Fprintln(w, "INDEX\tOPCODE\tDESC\t")
-	for i := 0; i <= len(b)-1; {
-		instr := vm.Instruction(b[i])
-		paramlength := 0
-		fmt.Fprintf(w, "%d\t0x%x\t%s\t\n", i, b[i], instr)
-		i++
-		if instr >= vm.PUSHBYTES1 && instr <= vm.PUSHBYTES75 {
-			paramlength = int(instr)
-		}
-		if instr == vm.JMP || instr == vm.JMPIF || instr == vm.JMPIFNOT || instr == vm.CALL {
-			paramlength = 2
-		}
-		for x := 0; x < paramlength; x++ {
-			fmt.Fprintf(w, "%d\t0x%x\t%s\t\n", i, b[i+1+x], string(b[i+1+x]))
-		}
-		i += paramlength
-	}
-	w.Flush()
+	v := vm.New(0)
+	v.LoadScript(b)
+	v.PrintOps()
 	return nil
 }
 

pkg/vm/vm.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"reflect"
 	"text/tabwriter"
+	"unicode/utf8"
 
 	"github.com/CityOfZion/neo-go/pkg/crypto/hash"
 	"github.com/CityOfZion/neo-go/pkg/crypto/keys"
@@ -119,19 +120,45 @@ func (v *VM) LoadArgs(method []byte, args []StackItem) {
 
 // PrintOps will print the opcodes of the current loaded program to stdout.
 func (v *VM) PrintOps() {
-	prog := v.Context().Program()
 	w := tabwriter.NewWriter(os.Stdout, 0, 0, 4, ' ', 0)
-	fmt.Fprintln(w, "INDEX\tOPCODE\tDESC\t")
-	cursor := ""
-	ip, _ := v.Context().CurrInstr()
-	for i := 0; i < len(prog); i++ {
-		if i == ip {
+	fmt.Fprintln(w, "INDEX\tOPCODE\tPARAMETER\t")
+	realctx := v.Context()
+	ctx := realctx.Copy()
+	ctx.ip = 0
+	ctx.nextip = 0
+	for {
+		cursor := ""
+		instr, parameter, err := ctx.Next()
+		if ctx.ip == realctx.ip {
 			cursor = "<<"
-		} else {
-			cursor = ""
 		}
-		fmt.Fprintf(w, "%d\t0x%2x\t%s\t%s\n", i, prog[i], Instruction(prog[i]).String(), cursor)
+		if err != nil {
+			fmt.Fprintf(w, "%d\t%s\tERROR: %s\t%s\n", ctx.ip, instr, err, cursor)
+			break
+		}
+		var desc = ""
+		if parameter != nil {
+			switch instr {
+			case JMP, JMPIF, JMPIFNOT, CALL:
+				offset := int16(binary.LittleEndian.Uint16(parameter))
+				desc = fmt.Sprintf("%d (%d/%x)", ctx.ip+int(offset), offset, parameter)
+			case SYSCALL:
+				desc = fmt.Sprintf("%q", parameter)
+			case APPCALL, TAILCALL:
+				desc = fmt.Sprintf("%x", parameter)
+			default:
+				if utf8.Valid(parameter) {
+					desc = fmt.Sprintf("%x (%q)", parameter, parameter)
+				} else {
+					desc = fmt.Sprintf("%x", parameter)
+				}
+			}
+		}
 
+		fmt.Fprintf(w, "%d\t%s\t%s\t%s\n", ctx.ip, instr, desc, cursor)
+		if ctx.nextip >= len(ctx.prog) {
+			break
+		}
 	}
 	w.Flush()
 }