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header.go
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/
header.go
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package fit
import (
"fmt"
"github.com/tormoder/fit/dyncrc16"
)
// Header represents a FIT file header.
type Header struct {
Size byte
ProtocolVersion byte
ProfileVersion uint16
DataSize uint32
DataType [4]byte
CRC uint16
}
var (
errNotFit = FormatError("header data type was not '.FIT'")
errHeaderSize = FormatError("illegal header size")
errHdrCRC = IntegrityError("header checksum failed")
)
func (d *decoder) decodeHeader() error {
size, err := d.r.ReadByte()
if err != nil {
return err
}
if size != headerSizeCRC && size != headerSizeNoCRC {
return errHeaderSize
}
d.h.Size = size
if err := d.readFull(d.tmp[:size-1]); err != nil {
return err
}
if err = checkProtocolVersion(d.tmp[0]); err != nil {
return err
}
d.h.ProtocolVersion = d.tmp[0]
d.h.ProfileVersion = le.Uint16(d.tmp[1:3])
d.h.DataSize = le.Uint32(d.tmp[3:7])
if string(d.tmp[7:11]) != fitDataTypeString {
return errNotFit
}
copy(d.h.DataType[:], d.tmp[7:11])
if size == headerSizeNoCRC {
return nil
}
d.h.CRC = le.Uint16(d.tmp[11:13])
if d.h.CRC == 0x0000 {
return nil
}
checksum := dyncrc16.New()
checksum.Write([]byte{size})
checksum.Write(d.tmp[:size-1])
if checksum.Sum16() != 0x0000 {
return errHdrCRC
}
return nil
}
func checkProtocolVersion(b byte) error {
if (b & protocolVersionMajorMask) > (protocolMajorVersion << protocolVersionMajorShift) {
err := fmt.Sprintf(
"protocol version %d.x not supported by sdk protocol version %d.%d",
(b&protocolVersionMajorMask)>>protocolVersionMajorShift,
protocolMajorVersion,
protocolMinorVersion)
return NotSupportedError(err)
}
return nil
}
// CheckIntegrity verifies the FIT header CRC.
func (h *Header) CheckIntegrity() error {
if err := checkProtocolVersion(h.ProtocolVersion); err != nil {
return err
}
if string(h.DataType[:len(h.DataType)]) != fitDataTypeString {
return errNotFit
}
if h.Size == headerSizeNoCRC {
return nil
}
if h.CRC == 0 {
return nil
}
crc := dyncrc16.New()
bh := make([]byte, h.Size)
bh[0] = h.Size
bh[1] = h.ProtocolVersion
le.PutUint16(bh[2:4], h.ProfileVersion)
le.PutUint32(bh[4:8], h.DataSize)
copy(bh[8:12], h.DataType[:])
le.PutUint16(bh[12:14], h.CRC)
if crc.Sum16() != 0x0000 {
return errHdrCRC
}
return nil
}
// MarshalJSON implements the json.Marshaler interface.
func (h *Header) MarshalJSON() ([]byte, error) {
e := newJSONEncodeState()
e.open()
e.writeFieldName("Size")
e.writeUint(uint64(h.Size))
e.c()
e.writeFieldName("ProtocolVersion")
e.writeUint(uint64(h.ProtocolVersion))
e.c()
e.writeFieldName("ProfileVersion")
e.writeUint(uint64(h.ProfileVersion))
e.c()
e.writeFieldName("DataSize")
e.writeUint(uint64(h.DataSize))
e.c()
e.writeFieldName("DataType")
e.writeStringBytes(h.DataType[:4])
e.c()
e.writeFieldName("CRC")
e.writeUint(uint64(h.CRC))
e.close()
return e.Bytes(), nil
}
func (h Header) String() string {
return fmt.Sprintf(
"size: %d | protover: %d | profver: %d | dsize: %d | dtype: %s | crc: %d",
h.Size, h.ProtocolVersion, h.ProfileVersion, h.DataSize, h.DataType, h.CRC,
)
}