Add Builder

pkg/vm/stack/builder.go

@@ -0,0 +1,177 @@
+package stack
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math/big"
+
+	"github.com/CityOfZion/neo-go/pkg/wire/util"
+)
+
+// Builder follows the builder pattern and will be used to build scripts
+type Builder struct {
+	w   *bytes.Buffer
+	err error
+}
+
+// NewBuilder returns a new builder object
+func NewBuilder() *Builder {
+	return &Builder{
+		w:   &bytes.Buffer{},
+		err: nil,
+	}
+}
+
+// Bytes returns the byte representation of the built buffer
+func (br *Builder) Bytes() []byte {
+	return br.w.Bytes()
+}
+
+// Emit a VM Opcode with data to the given buffer.
+func (br *Builder) Emit(op Instruction, b []byte) *Builder {
+	if br.err != nil {
+		return br
+	}
+	br.err = br.w.WriteByte(byte(op))
+	_, br.err = br.w.Write(b)
+	return br
+}
+
+// EmitOpcode emits a single VM Opcode the given buffer.
+func (br *Builder) EmitOpcode(op Instruction) *Builder {
+	if br.err != nil {
+		return br
+	}
+	br.err = br.w.WriteByte(byte(op))
+	return br
+}
+
+// EmitBool emits a bool type the given buffer.
+func (br *Builder) EmitBool(ok bool) *Builder {
+	if br.err != nil {
+		return br
+	}
+	op := PUSHT
+	if !ok {
+		op = PUSHF
+	}
+	return br.EmitOpcode(op)
+}
+
+// EmitInt emits a int type to the given buffer.
+func (br *Builder) EmitInt(i int64) *Builder {
+	if br.err != nil {
+		return br
+	}
+	if i == -1 {
+		return br.EmitOpcode(PUSHM1)
+	}
+	if i == 0 {
+		return br.EmitOpcode(PUSHF)
+	}
+	if i > 0 && i < 16 {
+		val := Instruction(int(PUSH1) - 1 + int(i))
+		return br.EmitOpcode(val)
+	}
+
+	bInt := big.NewInt(i)
+	val := reverse(bInt.Bytes())
+	return br.EmitBytes(val)
+}
+
+// EmitString emits a string to the given buffer.
+func (br *Builder) EmitString(s string) *Builder {
+	if br.err != nil {
+		return br
+	}
+	return br.EmitBytes([]byte(s))
+}
+
+// EmitBytes emits a byte array to the given buffer.
+func (br *Builder) EmitBytes(b []byte) *Builder {
+	if br.err != nil {
+		return br
+	}
+	var (
+		n = len(b)
+	)
+
+	if n <= int(PUSHBYTES75) {
+		return br.Emit(Instruction(n), b)
+	} else if n < 0x100 {
+		br.Emit(PUSHDATA1, []byte{byte(n)})
+	} else if n < 0x10000 {
+		buf := make([]byte, 2)
+		binary.LittleEndian.PutUint16(buf, uint16(n))
+		br.Emit(PUSHDATA2, buf)
+	} else {
+		buf := make([]byte, 4)
+		binary.LittleEndian.PutUint32(buf, uint32(n))
+		br.Emit(PUSHDATA4, buf)
+	}
+	_, br.err = br.w.Write(b)
+	return br
+}
+
+// EmitSyscall emits the syscall API to the given buffer.
+// Syscall API string cannot be 0.
+func (br *Builder) EmitSyscall(api string) *Builder {
+	if br.err != nil {
+		return br
+	}
+	if len(api) == 0 {
+		br.err = errors.New("syscall api cannot be of length 0")
+	}
+	buf := make([]byte, len(api)+1)
+	buf[0] = byte(len(api))
+	copy(buf[1:], []byte(api))
+	return br.Emit(SYSCALL, buf)
+}
+
+// EmitCall emits a call Opcode with label to the given buffer.
+func (br *Builder) EmitCall(op Instruction, label int16) *Builder {
+	return br.EmitJmp(op, label)
+}
+
+// EmitJmp emits a jump Opcode along with label to the given buffer.
+func (br *Builder) EmitJmp(op Instruction, label int16) *Builder {
+	if !isOpcodeJmp(op) {
+		br.err = fmt.Errorf("opcode %d is not a jump or call type", op)
+	}
+	buf := make([]byte, 2)
+	binary.LittleEndian.PutUint16(buf, uint16(label))
+	return br.Emit(op, buf)
+}
+
+// EmitAppCall emits an appcall, if tailCall is true, tailCall opcode will be
+// emitted instead.
+func (br *Builder) EmitAppCall(scriptHash util.Uint160, tailCall bool) *Builder {
+	op := APPCALL
+	if tailCall {
+		op = TAILCALL
+	}
+	return br.Emit(op, scriptHash.Bytes())
+}
+
+// EmitAppCallWithOperationAndData emits an appcall with the given operation and data.
+func (br *Builder) EmitAppCallWithOperationAndData(w *bytes.Buffer, scriptHash util.Uint160, operation string, data []byte) *Builder {
+	br.EmitBytes(data)
+	br.EmitString(operation)
+	return br.EmitAppCall(scriptHash, false)
+}
+
+// EmitAppCallWithOperation emits an appcall with the given operation.
+func (br *Builder) EmitAppCallWithOperation(scriptHash util.Uint160, operation string) *Builder {
+	br.EmitBool(false)
+	br.EmitString(operation)
+	return br.EmitAppCall(scriptHash, false)
+}
+
+func isOpcodeJmp(op Instruction) bool {
+	if op == JMP || op == JMPIFNOT || op == JMPIF || op == CALL {
+		return true
+	}
+	return false
+}