binary.Read()

binary_read.go

// Read reads structured binary data from r into data.
// Data must be a pointer to a fixed-size value or a slice
// of fixed-size values.
// Bytes read from r are decoded using the specified byte order
// and written to successive fields of the data.
// When decoding boolean values, a zero byte is decoded as false, and
// any other non-zero byte is decoded as true.
// When reading into structs, the field data for fields with
// blank (_) field names is skipped; i.e., blank field names
// may be used for padding.
// When reading into a struct, all non-blank fields must be exported
// or Read may panic.
//
// The error is EOF only if no bytes were read.
// If an EOF happens after reading some but not all the bytes,
// Read returns ErrUnexpectedEOF.
func Read(r io.Reader, order ByteOrder, data interface{}) error {
	// Fast path for basic types and slices.
	if n := intDataSize(data); n != 0 {
		bs := make([]byte, n)
		if _, err := io.ReadFull(r, bs); err != nil {
			return err
		}
		switch data := data.(type) {
		case *bool:
			*data = bs[0] != 0
		case *int8:
			*data = int8(bs[0])
		case *uint8:
			*data = bs[0]
		case *int16:
			*data = int16(order.Uint16(bs))
		case *uint16:
			*data = order.Uint16(bs)
		case *int32:
			*data = int32(order.Uint32(bs))
		case *uint32:
			*data = order.Uint32(bs)
		case *int64:
			*data = int64(order.Uint64(bs))
		case *uint64:
			*data = order.Uint64(bs)
		case *float32:
			*data = math.Float32frombits(order.Uint32(bs))
		case *float64:
			*data = math.Float64frombits(order.Uint64(bs))
		case []bool:
			for i, x := range bs { // Easier to loop over the input for 8-bit values.
				data[i] = x != 0
			}
		case []int8:
			for i, x := range bs {
				data[i] = int8(x)
			}
		case []uint8:
			copy(data, bs)
		case []int16:
			for i := range data {
				data[i] = int16(order.Uint16(bs[2*i:]))
			}
		case []uint16:
			for i := range data {
				data[i] = order.Uint16(bs[2*i:])
			}
		case []int32:
			for i := range data {
				data[i] = int32(order.Uint32(bs[4*i:]))
			}
		case []uint32:
			for i := range data {
				data[i] = order.Uint32(bs[4*i:])
			}
		case []int64:
			for i := range data {
				data[i] = int64(order.Uint64(bs[8*i:]))
			}
		case []uint64:
			for i := range data {
				data[i] = order.Uint64(bs[8*i:])
			}
		case []float32:
			for i := range data {
				data[i] = math.Float32frombits(order.Uint32(bs[4*i:]))
			}
		case []float64:
			for i := range data {
				data[i] = math.Float64frombits(order.Uint64(bs[8*i:]))
			}
		default:
			n = 0 // fast path doesn't apply
		}
		if n != 0 {
			return nil
		}
	}

	// Fallback to reflect-based decoding.
	v := reflect.ValueOf(data)
	size := -1
	switch v.Kind() {
	case reflect.Ptr:
		v = v.Elem()
		size = dataSize(v)
	case reflect.Slice:
		size = dataSize(v)
	}
	if size < 0 {
		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
	}
	d := &decoder{order: order, buf: make([]byte, size)}
	if _, err := io.ReadFull(r, d.buf); err != nil {
		return err
	}
	d.value(v)
	return nil
}