154 lines
3.5 KiB
Go
154 lines
3.5 KiB
Go
// Package skylab provides CAN packet encoding and decoding information based off
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// of skylab.yaml. It can convert packets to/from CAN raw bytes and JSON objects.
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package skylab
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import (
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"encoding/binary"
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"encoding/json"
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"fmt"
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"math"
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"time"
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// this is needed so that we can run make_skylab.go
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// without this, the yaml library will be removed
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// when we run `go mod tidy`
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"github.com/kschamplin/gotelem/internal/can"
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_ "gopkg.in/yaml.v3"
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)
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/*
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This file provides helpers used for serializing and deserializing skylab packets.
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It contains common code and interfaces.
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*/
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// float32ToBytes is an internal function used to encode a float value to bytes
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func float32ToBytes(b []byte, f float32, bigEndian bool) {
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bits := math.Float32bits(f)
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if bigEndian {
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binary.BigEndian.PutUint32(b, bits)
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} else {
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binary.LittleEndian.PutUint32(b, bits)
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}
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}
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// float32FromBytes is an internal function used to decode float value from bytes
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func float32FromBytes(b []byte, bigEndian bool) (f float32) {
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var bits uint32
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if bigEndian {
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bits = binary.BigEndian.Uint32(b)
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} else {
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bits = binary.LittleEndian.Uint32(b)
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}
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return math.Float32frombits(bits)
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}
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// Packet is any Skylab-generated packet.
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type Packet interface {
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Marshaler
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Unmarshaler
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Ider
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Sizer
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fmt.Stringer // to get the name
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}
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// Marshaler is a packet that can be marshalled into bytes.
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type Marshaler interface {
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MarshalPacket() ([]byte, error)
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}
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// Unmarshaler is a packet that can be unmarshalled from bytes.
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type Unmarshaler interface {
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UnmarshalPacket(p []byte) error
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}
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// Ider is a packet that can get its ID, based on the index of the packet, if any.
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type Ider interface {
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CanId() (can.CanID, error)
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}
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// Sizer allows for fast allocation.
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type Sizer interface {
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Size() uint
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}
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// CanSend takes a packet and makes CAN framing data.
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func ToCanFrame(p Packet) (f can.Frame, err error) {
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f.Id, err = p.CanId()
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if err != nil {
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return
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}
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f.Data, err = p.MarshalPacket()
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f.Kind = can.CanDataFrame
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return
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}
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// ---- other wire encoding business ----
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// internal structure for partially decoding json object.
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type RawJsonEvent struct {
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Timestamp int64 `json:"ts" db:"ts"`
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Name string `json:"name"`
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Data json.RawMessage `json:"data"`
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}
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// BusEvent is a timestamped Skylab packet - it contains
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type BusEvent struct {
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Timestamp time.Time `json:"ts"`
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Name string `json:"id"`
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Data Packet `json:"data"`
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}
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func (e BusEvent) MarshalJSON() (b []byte, err error) {
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// create the underlying raw event
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j := &RawJsonEvent{
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Timestamp: e.Timestamp.UnixMilli(),
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Name: e.Name,
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}
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// now we use the magic Packet -> map[string]interface{} function
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// FIXME: this uses reflection and isn't good for the economy
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j.Data, err = json.Marshal(e.Data)
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if err != nil {
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return nil, err
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}
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return json.Marshal(j)
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}
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func (e *BusEvent) UnmarshalJSON(b []byte) error {
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j := &RawJsonEvent{}
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err := json.Unmarshal(b, j)
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if err != nil {
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return err
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}
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e.Timestamp = time.UnixMilli(j.Timestamp)
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e.Name = j.Name
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e.Data, err = FromJson(j.Name, j.Data)
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return err
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}
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// we need to be able to parse the JSON as well. this is done using the
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// generator since we can use the switch/case thing since it's the fastest
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type UnknownIdError struct {
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id uint32
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}
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func (e *UnknownIdError) Error() string {
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return fmt.Sprintf("unknown id: %x", e.id)
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}
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type BadLengthError struct {
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expected uint32
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actual uint32
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}
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func (e *BadLengthError) Error() string {
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return fmt.Sprintf("bad data length, expected %d, got %d", e.expected, e.actual)
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}
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