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innosat_reader.go
49 lines (42 loc) · 1.23 KB
/
innosat_reader.go
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package extractors
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/howeyc/crc16"
"github.com/innosat-mats/rac-extract-payload/internal/innosat"
)
// SourcePackage ...
type SourcePackage struct {
Header *innosat.SourcePacketHeader
Payload *innosat.TMHeader
ApplicationPayload []byte
}
const crcChecksumLength int = 2
const pusLengthOffset int = 1
// DecodeSource decodes a byte array to a SourcePackage
func DecodeSource(data []byte) (SourcePackage, error) {
var err error
buf := bytes.NewReader(data)
header, err := innosat.NewSourcePacketHeader(buf)
if err != nil {
return SourcePackage{}, err
}
if crc16.ChecksumCCITTFalse(data[:len(data)-crcChecksumLength]) != binary.BigEndian.Uint16(data[len(data)-crcChecksumLength:]) {
return SourcePackage{}, fmt.Errorf(
"checksum bad %d",
crc16.ChecksumCCITTFalse(data[:len(data)-crcChecksumLength]),
)
}
tmHeader, err := innosat.NewTMHeader(buf)
if err != nil {
return SourcePackage{}, err
}
sliceStart := binary.Size(header) + binary.Size(tmHeader)
sliceEnd := sliceStart + int(header.PacketLength) - binary.Size(tmHeader) - crcChecksumLength + pusLengthOffset
return SourcePackage{
header,
tmHeader,
data[sliceStart:sliceEnd],
}, nil
}