Initial commit

Signed-off-by: Thomas Klaehn <thomas.klaehn@perinet.io>

fitparser/header.go

@@ -0,0 +1,110 @@
+package fitparser
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+)
+
+// Header represents a FIT file header
+type Header struct {
+	Size            uint8  // Header size (12 or 14 bytes)
+	ProtocolVersion uint8  // Protocol version
+	ProfileVersion  uint16 // Profile version
+	DataSize        uint32 // Size of data records in bytes
+	DataType        [4]byte // ".FIT" signature
+	CRC             uint16 // CRC of header (only present if Size == 14)
+}
+
+// ParseHeader parses a FIT file header from the given data
+func ParseHeader(data []byte) (*Header, error) {
+	if len(data) < HeaderMinSize {
+		return nil, fmt.Errorf("header too small: got %d bytes, need at least %d", len(data), HeaderMinSize)
+	}
+
+	h := &Header{
+		Size:            data[0],
+		ProtocolVersion: data[1],
+		DataType:        [4]byte{data[8], data[9], data[10], data[11]},
+	}
+
+	// Validate header size
+	if h.Size != HeaderWithCRCSize && h.Size != HeaderWithoutCRCSize {
+		return nil, fmt.Errorf("invalid header size: %d (expected %d or %d)",
+			h.Size, HeaderWithoutCRCSize, HeaderWithCRCSize)
+	}
+
+	// Ensure we have enough data
+	if len(data) < int(h.Size) {
+		return nil, fmt.Errorf("insufficient data for header: got %d bytes, need %d", len(data), h.Size)
+	}
+
+	// Parse profile version (little endian)
+	h.ProfileVersion = binary.LittleEndian.Uint16(data[2:4])
+
+	// Parse data size (little endian)
+	h.DataSize = binary.LittleEndian.Uint32(data[4:8])
+
+	// Validate signature
+	if h.DataType != FITSignature {
+		return nil, fmt.Errorf("invalid FIT signature: got %s, expected .FIT", string(h.DataType[:]))
+	}
+
+	// Parse CRC if present
+	if h.Size == HeaderWithCRCSize {
+		h.CRC = binary.LittleEndian.Uint16(data[12:14])
+
+		// Validate header CRC
+		calculatedCRC := CalculateCRC(data[0:12])
+		if calculatedCRC != h.CRC {
+			return nil, fmt.Errorf("header CRC mismatch: got 0x%04X, expected 0x%04X", h.CRC, calculatedCRC)
+		}
+	}
+
+	return h, nil
+}
+
+// Validate performs basic validation on the header
+func (h *Header) Validate() error {
+	if h.Size != HeaderWithCRCSize && h.Size != HeaderWithoutCRCSize {
+		return fmt.Errorf("invalid header size: %d", h.Size)
+	}
+
+	if h.DataType != FITSignature {
+		return fmt.Errorf("invalid FIT signature: %s", string(h.DataType[:]))
+	}
+
+	protocolMajor := h.ProtocolVersion >> ProtocolVersionMajorShift
+	if protocolMajor < 1 || protocolMajor > 2 {
+		return fmt.Errorf("unsupported protocol version: %d.%d",
+			protocolMajor, h.ProtocolVersion&ProtocolVersionMinorMask)
+	}
+
+	return nil
+}
+
+// ProtocolVersionMajor returns the major version of the protocol
+func (h *Header) ProtocolVersionMajor() uint8 {
+	return h.ProtocolVersion >> ProtocolVersionMajorShift
+}
+
+// ProtocolVersionMinor returns the minor version of the protocol
+func (h *Header) ProtocolVersionMinor() uint8 {
+	return h.ProtocolVersion & ProtocolVersionMinorMask
+}
+
+// IsFIT checks if the given data starts with a valid FIT file signature
+func IsFIT(data []byte) bool {
+	if len(data) < HeaderMinSize {
+		return false
+	}
+
+	signature := [4]byte{data[8], data[9], data[10], data[11]}
+	return bytes.Equal(signature[:], FITSignature[:])
+}
+
+// String returns a string representation of the header
+func (h *Header) String() string {
+	return fmt.Sprintf("FIT Header: Protocol v%d.%d, Profile v%d, DataSize=%d bytes, HeaderSize=%d bytes",
+		h.ProtocolVersionMajor(), h.ProtocolVersionMinor(), h.ProfileVersion, h.DataSize, h.Size)
+}