btcwire.go

package util

import (
	"encoding/binary"
	"fmt"
	"io"
	"time"

	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
)

const (
	// MaxVarIntPayload is the maximum payload size for a variable length integer.
	MaxVarIntPayload = 9

	// binaryFreeListMaxItems is the number of buffers to keep in the free
	// list to use for binary serialization and deserialization.
	binaryFreeListMaxItems = 1024
)

var (
	// littleEndian is a convenience variable since binary.LittleEndian is
	// quite long.
	littleEndian = binary.LittleEndian

	// bigEndian is a convenience variable since binary.BigEndian is quite
	// long.
	bigEndian = binary.BigEndian
)

// binaryFreeList defines a concurrent safe free list of byte slices (up to the
// maximum number defined by the binaryFreeListMaxItems constant) that have a
// cap of 8 (thus it supports up to a uint64).  It is used to provide temporary
// buffers for serializing and deserializing primitive numbers to and from their
// binary encoding in order to greatly reduce the number of allocations
// required.
//
// For convenience, functions are provided for each of the primitive unsigned
// integers that automatically obtain a buffer from the free list, perform the
// necessary binary conversion, read from or write to the given io.Reader or
// io.Writer, and return the buffer to the free list.
type binaryFreeList chan []byte

// Borrow returns a byte slice from the free list with a length of 8.  A new
// buffer is allocated if there are not any available on the free list.
func (l binaryFreeList) Borrow() []byte {
	var buf []byte
	select {
	case buf = <-l:
	default:
		buf = make([]byte, 8)
	}
	return buf[:8]
}

// Return puts the provided byte slice back on the free list.  The buffer MUST
// have been obtained via the Borrow function and therefore have a cap of 8.
func (l binaryFreeList) Return(buf []byte) {
	select {
	case l <- buf:
	default:
		// Let it go to the garbage collector.
	}
}

// Uint8 reads a single byte from the provided reader using a buffer from the
// free list and returns it as a uint8.
func (l binaryFreeList) Uint8(r io.Reader) (uint8, error) {
	buf := l.Borrow()[:1]
	if _, err := io.ReadFull(r, buf); err != nil {
		l.Return(buf)
		return 0, err
	}
	rv := buf[0]
	l.Return(buf)
	return rv, nil
}

// Uint16 reads two bytes from the provided reader using a buffer from the
// free list, converts it to a number using the provided byte order, and returns
// the resulting uint16.
func (l binaryFreeList) Uint16(r io.Reader, byteOrder binary.ByteOrder) (uint16, error) {
	buf := l.Borrow()[:2]
	if _, err := io.ReadFull(r, buf); err != nil {
		l.Return(buf)
		return 0, err
	}
	rv := byteOrder.Uint16(buf)
	l.Return(buf)
	return rv, nil
}

// Uint32 reads four bytes from the provided reader using a buffer from the
// free list, converts it to a number using the provided byte order, and returns
// the resulting uint32.
func (l binaryFreeList) Uint32(r io.Reader, byteOrder binary.ByteOrder) (uint32, error) {
	buf := l.Borrow()[:4]
	if _, err := io.ReadFull(r, buf); err != nil {
		l.Return(buf)
		return 0, err
	}
	rv := byteOrder.Uint32(buf)
	l.Return(buf)
	return rv, nil
}

// Uint64 reads eight bytes from the provided reader using a buffer from the
// free list, converts it to a number using the provided byte order, and returns
// the resulting uint64.
func (l binaryFreeList) Uint64(r io.Reader, byteOrder binary.ByteOrder) (uint64, error) {
	buf := l.Borrow()[:8]
	if _, err := io.ReadFull(r, buf); err != nil {
		l.Return(buf)
		return 0, err
	}
	rv := byteOrder.Uint64(buf)
	l.Return(buf)
	return rv, nil
}

// PutUint8 copies the provided uint8 into a buffer from the free list and
// writes the resulting byte to the given writer.
func (l binaryFreeList) PutUint8(w io.Writer, val uint8) error {
	buf := l.Borrow()[:1]
	buf[0] = val
	_, err := w.Write(buf)
	l.Return(buf)
	return err
}

// PutUint16 serializes the provided uint16 using the given byte order into a
// buffer from the free list and writes the resulting two bytes to the given
// writer.
func (l binaryFreeList) PutUint16(w io.Writer, byteOrder binary.ByteOrder, val uint16) error {
	buf := l.Borrow()[:2]
	byteOrder.PutUint16(buf, val)
	_, err := w.Write(buf)
	l.Return(buf)
	return err
}

// PutUint32 serializes the provided uint32 using the given byte order into a
// buffer from the free list and writes the resulting four bytes to the given
// writer.
func (l binaryFreeList) PutUint32(w io.Writer, byteOrder binary.ByteOrder, val uint32) error {
	buf := l.Borrow()[:4]
	byteOrder.PutUint32(buf, val)
	_, err := w.Write(buf)
	l.Return(buf)
	return err
}

// PutUint64 serializes the provided uint64 using the given byte order into a
// buffer from the free list and writes the resulting eight bytes to the given
// writer.
func (l binaryFreeList) PutUint64(w io.Writer, byteOrder binary.ByteOrder, val uint64) error {
	buf := l.Borrow()[:8]
	byteOrder.PutUint64(buf, val)
	_, err := w.Write(buf)
	l.Return(buf)
	return err
}

// binarySerializer provides a free list of buffers to use for serializing and
// deserializing primitive integer values to and from io.Readers and io.Writers.
var binarySerializer binaryFreeList = make(chan []byte, binaryFreeListMaxItems)

// Uint32Time represents a unix timestamp encoded with a uint32.  It is used as
// a way to signal the readElement function how to decode a timestamp into a Go
// time.Time since it is otherwise ambiguous.
type Uint32Time time.Time

// Int64Time represents a unix timestamp encoded with an int64.  It is used as
// a way to signal the readElement function how to decode a timestamp into a Go
// time.Time since it is otherwise ambiguous.
type Int64Time time.Time

// readElement reads the next sequence of bytes from r using little endian
// depending on the concrete type of element pointed to.
func ReadElement(r io.Reader, element interface{}) error {
	// Attempt to read the element based on the concrete type via fast
	// type assertions first.
	switch e := element.(type) {
	case *int32:
		rv, err := binarySerializer.Uint32(r, littleEndian)
		if err != nil {
			return err
		}
		*e = int32(rv)
		return nil

	case *uint32:
		rv, err := binarySerializer.Uint32(r, littleEndian)
		if err != nil {
			return err
		}
		*e = rv
		return nil

	case *int64:
		rv, err := binarySerializer.Uint64(r, littleEndian)
		if err != nil {
			return err
		}
		*e = int64(rv)
		return nil

	case *uint64:
		rv, err := binarySerializer.Uint64(r, littleEndian)
		if err != nil {
			return err
		}
		*e = rv
		return nil

	case *bool:
		rv, err := binarySerializer.Uint8(r)
		if err != nil {
			return err
		}
		if rv == 0x00 {
			*e = false
		} else {
			*e = true
		}
		return nil

	// Unix timestamp encoded as a uint32.
	case *Uint32Time:
		rv, err := binarySerializer.Uint32(r, binary.LittleEndian)
		if err != nil {
			return err
		}
		*e = Uint32Time(time.Unix(int64(rv), 0))
		return nil

	// Unix timestamp encoded as an int64.
	case *Int64Time:
		rv, err := binarySerializer.Uint64(r, binary.LittleEndian)
		if err != nil {
			return err
		}
		*e = Int64Time(time.Unix(int64(rv), 0))
		return nil

	// Message header checksum.
	case *[4]byte:
		_, err := io.ReadFull(r, e[:])
		if err != nil {
			return err
		}
		return nil

	// IP address.
	case *[16]byte:
		_, err := io.ReadFull(r, e[:])
		if err != nil {
			return err
		}
		return nil

	case *chainhash.Hash:
		_, err := io.ReadFull(r, e[:])
		if err != nil {
			return err
		}
		return nil

	}

	// Fall back to the slower binary.Read if a fast path was not available
	// above.
	return binary.Read(r, littleEndian, element)
}

// readElements reads multiple items from r.  It is equivalent to multiple
// calls to readElement.
func ReadElements(r io.Reader, elements ...interface{}) error {
	for _, element := range elements {
		err := ReadElement(r, element)
		if err != nil {
			return err
		}
	}
	return nil
}

// ReadVarInt reads a variable length integer from r and returns it as a uint64.
func ReadVarInt(r io.Reader, pver uint32) (uint64, error) {
	discriminant, err := binarySerializer.Uint8(r)
	if err != nil {
		return 0, err
	}

	var rv uint64
	switch discriminant {
	case 0xff:
		sv, err := binarySerializer.Uint64(r, littleEndian)
		if err != nil {
			return 0, err
		}
		rv = sv

		// The encoding is not canonical if the value could have been
		// encoded using fewer bytes.
		min := uint64(0x100000000)
		if rv < min {
			return 0, fmt.Errorf("RV < MIN")
		}

	case 0xfe:
		sv, err := binarySerializer.Uint32(r, littleEndian)
		if err != nil {
			return 0, err
		}
		rv = uint64(sv)

		// The encoding is not canonical if the value could have been
		// encoded using fewer bytes.
		min := uint64(0x10000)
		if rv < min {
			return 0, fmt.Errorf("RV < MIN")
		}

	case 0xfd:
		sv, err := binarySerializer.Uint16(r, littleEndian)
		if err != nil {
			return 0, err
		}
		rv = uint64(sv)

		// The encoding is not canonical if the value could have been
		// encoded using fewer bytes.
		min := uint64(0xfd)
		if rv < min {
			return 0, fmt.Errorf("RV < MIN")
		}

	default:
		rv = uint64(discriminant)
	}

	return rv, nil
}

// ReadVarBytes reads a variable length byte array.  A byte array is encoded
// as a varInt containing the length of the array followed by the bytes
// themselves.  An error is returned if the length is greater than the
// passed maxAllowed parameter which helps protect against memory exhaustion
// attacks and forced panics through malformed messages.  The fieldName
// parameter is only used for the error message so it provides more context in
// the error.
func ReadVarBytes(r io.Reader, pver uint32, maxAllowed uint32,
	fieldName string) ([]byte, error) {

	count, err := ReadVarInt(r, pver)
	if err != nil {
		return nil, err
	}

	// Prevent byte array larger than the max message size.  It would
	// be possible to cause memory exhaustion and panics without a sane
	// upper bound on this count.
	if count > uint64(maxAllowed) {
		str := fmt.Sprintf("%s is larger than the max allowed size "+
			"[count %d, max %d]", fieldName, count, maxAllowed)
		return nil, fmt.Errorf(str)
	}

	b := make([]byte, count)
	_, err = io.ReadFull(r, b)
	if err != nil {
		return nil, err
	}
	return b, nil
}

// ReadScript reads a variable length byte array that represents a transaction
// script.  It is encoded as a varInt containing the length of the array
// followed by the bytes themselves.  An error is returned if the length is
// greater than the passed maxAllowed parameter which helps protect against
// memory exhaustion attacks and forced panics through malformed messages.  The
// fieldName parameter is only used for the error message so it provides more
// context in the error.
func ReadScript(r io.Reader, fieldName string) ([]byte, error) {
	count, err := ReadVarInt(r, 0)
	if err != nil {
		return nil, err
	}

	b := make([]byte, count)
	_, err = io.ReadFull(r, b)
	if err != nil {
		return nil, err
	}
	return b, nil
}

// ReadTxIn reads the next sequence of bytes from r as a transaction input
// (TxIn).
func ReadTxIn(r io.Reader, ti *wire.TxIn) error {
	err := ReadOutPoint(r, &ti.PreviousOutPoint)
	if err != nil {
		return err
	}

	ti.SignatureScript, err = ReadScript(r, "transaction input signature script")
	if err != nil {
		return err
	}

	return ReadElement(r, &ti.Sequence)
}

// ReadTxOut reads the next sequence of bytes from r as a transaction output
// (TxOut).
func ReadTxOut(r io.Reader, to *wire.TxOut) error {
	err := ReadElement(r, &to.Value)
	if err != nil {
		return err
	}

	to.PkScript, err = ReadScript(r, "transaction output public key script")
	return err
}

// ReadOutPoint reads the next sequence of bytes from r as an OutPoint.
func ReadOutPoint(r io.Reader, op *wire.OutPoint) error {
	_, err := io.ReadFull(r, op.Hash[:])
	if err != nil {
		return err
	}

	op.Index, err = binarySerializer.Uint32(r, littleEndian)
	return err
}