psmb

README

psmb

Proactive service library for modbusd

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Continuous Integration

I do continuous integration and deploy docker images after git push by self-hosted drone.io server, circleci service, codecov service and dockerhub service.

CI Server	Target	Status
Travis	API
CircleCI	x86
Drone	armhf

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Environment variables

Why environment variable? Refer to the 12 factors

• CONF_PSMBTCP: config file path
• EP_BACKEND: endpoint of remote service discovery server (optional)

Contracts (Interfaces)

• IProactiveService: proactive service
• IReaderTaskDataStore: read/poll task data store
• IWriterTaskDataStore: write task data store
• IHistoryDataStore: history data store
• IFilterDataStore: filter data store
• IConfig: config management

Golang package management

• I adopted glide as package management system for this repository.

Worker Pool Model

Request from upstream

Response from downstream

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Up and Running

Docker Compose

docker-compose build --pull
docker-compose up

Manually

Install libzmq (3.2.5)

wget https://github.com/zeromq/zeromq3-x/releases/download/v3.2.5/zeromq-3.2.5.tar.gz
tar xvzf zeromq-3.2.5.tar.gz
cd zeromq-3.2.5
./configure
make
sudo make install
sudo ldconfig

Build

# install glide
curl https://glide.sh/get | sh

# install dependencies
glide up

# build
cd tcp-srv
go build -o psmbtcp-srv

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Deployment Diagram

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Unit tests

• binary
• types

Test cases

Binary

• Bytes to 16-bit integer array tests
  • BytesToUInt16s in big endian order - (1/4)
  • BytesToUInt16s in little endian order - (2/4)
  • BytesToInt16s in big endian order - (3/4)
  • BytesToInt16s in little endian order - (4/4)
• Bytes to 32-bit integer array tests
  • BytesToUInt32s in (ABCD) Big Endian order - (1/4)
  • BytesToUInt32s in (DCBA) Little Endian order - (2/4)
  • BytesToUInt32s in (BADC) Mid-Big Endian order - (3/4)
  • BytesToUInt32s in (CDAB) Mid-Little Endian order - (4/4)
  • BytesToInt32s in (ABCD) Big Endian order - (1/4)
  • BytesToInt32s in (DCBA) Little Endian order - (2/4)
  • BytesToInt32s in (BADC) Mid-Big Endian order - (3/4)
  • BytesToInt32s in (CDAB) Mid-Little Endian order - (4/4)
• Bytes to 32-bit float array tests
  • BytesToFloat32s in (ABCD) Big Endian order - (1/4)
  • BytesToFloat32s in (DCBA) Little Endian order - (2/4)
  • BytesToFloat32s in (BADC) Mid-Big Endian order - (3/4)
  • BytesToFloat32s in (CDAB) Mid-Little Endian order - (4/4)
• Bytes/registers utility tests
  • BitStringToUInt8s test
  • BitStringToUInt8s test - left comma
  • BitStringToUInt8s test - right comma
  • BitStringToUInt8s test - left, right comma
  • RegistersToBytes test
  • BytesToHexString test
  • DecimalStringToRegisters test
  • DecimalStringToRegisters test - left comma
  • DecimalStringToRegisters test - right comma
  • DecimalStringToRegisters test - left, right comma
  • HexStringToRegisters test
  • HexStringToRegisters test - wrong length
  • LinearScalingRegisters test
  • LinearScalingRegisters test - (0,0,0,0)
  • LinearScalingRegisters test - reverse

Types

Upstream structure test

• One-off modbus tcp struct tests
  • mbtcp.once.read request test
  • mbtcp.once.read response test
• get/set modbus tcp timeout struct tests
  • mbtcp.timeout.read request test
  • mbtcp.timeout.read response test
  • mbtcp.timeout.update request test
  • mbtcp.timeout.update response test
  • mbtcp.once.write request test
  • mbtcp.once.write response test

Downstream structure test

• modbus tcp downstreamstruct tests
  • read request test
  • single read response test
  • multiple read response test
  • single write request test
  • multiple write request test
  • set timeout request test
  • get timeout response test

---

UML

---

License

MIT

Documentation

Overview

Package psmb a proactive service library for modbus daemon.

Define high-level Contracts(interface) and data types.

By taka@cmwang.net

Index

• Variables
• func BitStringToUInt8s(bitString string) ([]uint8, error)
• func BytesToFloat32s(buf []byte, endian Endian) ([]float32, error)
• func BytesToHexString(bytes []byte) string
• func BytesToInt16s(buf []byte, endian Endian) ([]int16, error)
• func BytesToInt32s(buf []byte, endian Endian) ([]int32, error)
• func BytesToUInt16s(buf []byte, endian Endian) ([]uint16, error)
• func BytesToUInt32s(buf []byte, endian Endian) ([]uint32, error)
• func DecimalStringToRegisters(decString string) ([]uint16, error)
• func HexStringToRegisters(hexString string) ([]uint16, error)
• func LinearScalingRegisters(data []uint16, domainLow, domainHigh, rangeLow, rangeHigh float64) ([]float32, error)
• func RegistersToBytes(data []uint16) ([]byte, error)
• type DMbtcpReadReq
• type DMbtcpRes
• type DMbtcpTimeout
• type DMbtcpWriteReq
• type Endian
• type FilterType
• type HistoryData
• type IConfig
• type IFilterDataStore
• type IHistoryDataStore
• type IProactiveService
• type IReaderTaskDataStore
• type IWriterTaskDataStore
• type JSONableByteSlice
  • func (u JSONableByteSlice) MarshalJSON() ([]byte, error)
• type MbtcpFilterOpReq
• type MbtcpFilterStatus
• type MbtcpFiltersStatus
• type MbtcpHistoryData
• type MbtcpPollData
• type MbtcpPollOpReq
• type MbtcpPollStatus
• type MbtcpPollsStatus
• type MbtcpReadReq
• type MbtcpReadRes
• type MbtcpSimpleRes
• type MbtcpTimeoutReq
• type MbtcpTimeoutRes
• type MbtcpWriteReq
• type ReaderTask
• type RegValueType
• type ScaleRange

Variables

var (
	// ErrBitStringToUInt8s is the error of BitStringToUInt8s conversion.
	ErrBitStringToUInt8s = errors.New("Fail to convert bit string to uint8 array")

	// ErrDecimalStringToRegisters is the error of DecimalStringToRegisters conversion.
	ErrDecimalStringToRegisters = errors.New("Fail to convert decimal string to uint16/words array in big endian order")

	// ErrHexStringToRegisters is the error of HexStringToRegisters conversion.
	ErrHexStringToRegisters = errors.New("Fail to convert hexadecimal string to uint16/words array in big endian order")

	// ErrRegistersToBytes is the error of RegistersToBytes conversion.
	ErrRegistersToBytes = errors.New("Fail to convert registers/uint16 array to byte array in big endian order")

	// ErrBytesToFloat32s is the error of BytesToFloat32s conversion.
	ErrBytesToFloat32s = errors.New("Fail to convert byte array to float32 array in four endian orders")

	// ErrNotANumber is the error of LinearScalingRegisters conversion.
	ErrNotANumber = errors.New("Fail to scale the registers linearly")

	// ErrBytesToInt32s is the error of BytesToInt32s conversion.
	ErrBytesToInt32s = errors.New("Fail to convert byte array to UInt32 array in four endian orders")

	// ErrBytesToUInt32s is the error of BytesToUInt32s conversion.
	ErrBytesToUInt32s = errors.New("Fail to convert byte array to UInt32 array in four endian orders")

	// ErrBytesToInt16s is the error of BytesToInt16s conversion.
	ErrBytesToInt16s = errors.New("Fail to convert byte array to Int16 array in two endian orders")

	// ErrBytesToUInt16s is the error of BytesToUInt16s conversion.
	ErrBytesToUInt16s = errors.New("Fail to convert byte array to UInt16 array in two endian orders")

	// ErrInvalidLengthToConvert is the error of invalid length to convert
	ErrInvalidLengthToConvert = errors.New("Invalid length to convert")
)

Functions

func BitStringToUInt8s

func BitStringToUInt8s(bitString string) ([]uint8, error)

BitStringToUInt8s converts bits string to uint8 array.

source: function code 15

func BytesToFloat32s

func BytesToFloat32s(buf []byte, endian Endian) ([]float32, error)

BytesToFloat32s converts byte array to float32 array in four endian orders. i.e.,

BigEndian (0),
LittleEndian (1)
MidBigEndian (2)
MidLittleEndian (3)

func BytesToHexString

func BytesToHexString(bytes []byte) string

BytesToHexString converts bytes array to hexadecimal string.

example: 112C004F12345678

func BytesToInt16s

func BytesToInt16s(buf []byte, endian Endian) ([]int16, error)

BytesToInt16s converts byte array to Int16 array in two endian orders. i.e.,

BigEndian (0) or LittleEndian (1)

func BytesToInt32s

func BytesToInt32s(buf []byte, endian Endian) ([]int32, error)

BytesToInt32s converts byte array to Int32 array in four endian orders. i.e.,

BigEndian (0),
LittleEndian (1)
MidBigEndian (2)
MidLittleEndian (3)

func BytesToUInt16s

func BytesToUInt16s(buf []byte, endian Endian) ([]uint16, error)

BytesToUInt16s converts byte array to UInt16 array in two endian orders. i.e.,

BigEndian (0) or LittleEndian (1)

func BytesToUInt32s

func BytesToUInt32s(buf []byte, endian Endian) ([]uint32, error)

BytesToUInt32s converts byte array to UInt32 array in four endian orders. i.e.,

BigEndian (0),
LittleEndian (1)
MidBigEndian (2)
MidLittleEndian (3)

func DecimalStringToRegisters

func DecimalStringToRegisters(decString string) ([]uint16, error)

DecimalStringToRegisters converts decimal string to uint16/words array in big endian order.

limitation: leading space before comma is not allowed.
source: upstream.

func HexStringToRegisters

func HexStringToRegisters(hexString string) ([]uint16, error)

HexStringToRegisters converts hexadecimal string to uint16/words array in big endian order.

source: upstream.

func LinearScalingRegisters

func LinearScalingRegisters(data []uint16, domainLow, domainHigh, rangeLow, rangeHigh float64) ([]float32, error)

LinearScalingRegisters scales the registers linearly. Equation:

Let domainLow, domainHigh, rangeLow, rangeHigh as a, b, c, d accordingly.
Output = c + (d - c) * (input - a) / (b - a)

func RegistersToBytes

func RegistersToBytes(data []uint16) ([]byte, error)

RegistersToBytes converts registers/uint16 array to byte array in big endian order.

source: downstream.

Types

type DMbtcpReadReq

type DMbtcpReadReq struct {
	// Tid unique transaction id in `string` format
	Tid string `json:"tid"`
	// Cmd modbusd command type: https://github.com/taka-wang/modbusd#command-mapping-table
	Cmd int `json:"cmd"`
	// IP ip address or hostname of the modbus tcp slave
	IP string `json:"ip"`
	// Port port number of the modbus tcp slave
	Port string `json:"port"`
	// Slave device id of the modbus tcp slave
	Slave uint8 `json:"slave"`
	// Addr start address for read
	Addr uint16 `json:"addr"`
	// Len the length of registers or bits
	Len uint16 `json:"len"`
}

DMbtcpReadReq downstream modbus tcp read request

type DMbtcpRes

type DMbtcpRes struct {
	// Tid unique transaction id in string format
	Tid string `json:"tid"`
	// Status response status string
	Status string `json:"status"`
	// Data for 'read function code' only.
	Data []uint16 `json:"data,omitempty"`
}

DMbtcpRes downstream modbus tcp read/write response

type DMbtcpTimeout

type DMbtcpTimeout struct {
	// Tid unique transaction id in `string` format
	Tid string `json:"tid"`
	// Cmd modbusd command type: https://github.com/taka-wang/modbusd#command-mapping-table
	Cmd int `json:"cmd"`
	// Status for response only.
	Status string `json:"status,omitempty"`
	// Timeout set timeout request and get timeout response only.
	Timeout int64 `json:"timeout,omitempty"`
}

DMbtcpTimeout downstream modbus tcp set/get timeout request/response

type DMbtcpWriteReq

type DMbtcpWriteReq struct {
	// Tid unique transaction id in `string` format
	Tid string `json:"tid"`
	// Cmd modbusd command type: https://github.com/taka-wang/modbusd#command-mapping-table
	Cmd int `json:"cmd"`
	// IP ip address or hostname of the modbus tcp slave
	IP string `json:"ip"`
	// Port port number of the modbus tcp slave
	Port string `json:"port"`
	// Slave device id of the modbus tcp slave
	Slave uint8 `json:"slave"`
	// Addr start address for write
	Addr uint16 `json:"addr"`
	// Len omit for fc5, fc6
	Len uint16 `json:"len,omitempty"`
	// Data should be []uint16, uint16 (FC5, FC6)
	Data interface{} `json:"data"`
}

DMbtcpWriteReq downstream modbus tcp write single bit/register request

type Endian

type Endian int

Endian defines byte endianness

const (

	// AB 16-bit words may be represented in big-endian format
	AB Endian
	// BA 16-bit words may be represented in little-endian format
	BA
)

16-bits Endian

const (

	// ABCD 32-bit words may be represented in big-endian format
	ABCD Endian
	// DCBA 32-bit words may be represented in little-endian format
	DCBA
	// BADC 32-bit words may be represented in mid-big-endian format
	BADC
	// CDAB 32-bit words may be represented in mid-little-endian format
	CDAB
)

32-bits Endian

const (

	// BigEndian 32-bit words may be represented in ABCD format
	BigEndian Endian
	// LittleEndian 32-bit words may be represented in DCBA format
	LittleEndian
	// MidBigEndian 32-bit words may be represented in BADC format
	MidBigEndian
	// MidLittleEndian 32-bit words may be represented in CDAB format
	MidLittleEndian
)

32-bits Endian

type FilterType

type FilterType int

FilterType filter type

const (
	// Change change or not
	Change FilterType = iota
	// GreaterEqual greater than or equal
	GreaterEqual
	// Greater greater than
	Greater
	// Equal equal
	Equal
	// Less less than
	Less
	// LessEqual less than or equal
	LessEqual
	// InsideRange inside range
	InsideRange
	// InsideIncRange inside range (include)
	InsideIncRange
	// OutsideRange outside range
	OutsideRange
	// OutsideIncRange outside range (include)
	OutsideIncRange
)

Filter value type

type HistoryData

type HistoryData struct {
	Ts   int64       `json:"ts,omitempty"`
	Data interface{} `json:"data,omitempty"` // universal data container
}

HistoryData history data

type IConfig

type IConfig interface {
	// contains filtered or unexported methods
}

IConfig config interface

type IFilterDataStore

type IFilterDataStore interface {
	// Add add request to filter map
	Add(name string, req interface{}) error
	// Get get request from filter map
	Get(name string) (interface{}, bool)
	// GetAll get all request from filter map
	GetAll() interface{}
	// Delete delete request from filter map
	Delete(name string)
	// DeleteAll delete all requests from filter map
	DeleteAll()
	// UpdateToggle update filter request enabled flag
	UpdateToggle(name string, toggle bool) error
	// UpdateAllToggles update all filter requests enabled flag
	UpdateAllToggles(toggle bool)
}

IFilterDataStore filter interface

type IHistoryDataStore

type IHistoryDataStore interface {
	// Add add history
	Add(name string, data interface{}) error
	// Get get history within range
	Get(name string, limit int) (map[string]string, error)
	// GetAll get all history
	GetAll(name string) (map[string]string, error)
	// GetLatest get latest history
	GetLatest(name string) (string, error)
}

IHistoryDataStore history interface

type IProactiveService

type IProactiveService interface {
	// Start enable proactive service
	Start()
	// Stop disable proactive service
	Stop()
	// ParseRequest parse requests from IT
	ParseRequest(msg []string) (interface{}, error)
	// HandleRequest handle requests from IT
	HandleRequest(cmd string, r interface{}) error
	// ParseResponse parse responses from OT
	ParseResponse(msg []string) (interface{}, error)
	// HandleResponse handle responses from OT
	HandleResponse(cmd string, r interface{}) error
}

IProactiveService proactive service contracts, all services should implement the following methods.

type IReaderTaskDataStore

type IReaderTaskDataStore interface {
	// Add add request to read/poll task map
	Add(name, tid, cmd string, req interface{}) error

	// GetTaskByID get request via TID from read/poll task map
	GetTaskByID(tid string) (interface{}, bool)

	// GetTaskByName get request via poll name from read/poll task map
	GetTaskByName(name string) (interface{}, bool)

	// GetAll get all requests from read/poll task map
	//	ex: mbtcp: []MbtcpPollStatus
	GetAll() interface{}

	// DeleteAll remove all requests from read/poll task map
	DeleteAll()

	// DeleteTaskByID remove request from via TID from read/poll task map
	DeleteTaskByID(tid string)

	// DeleteTaskByName remove request via poll name from read/poll task map
	DeleteTaskByName(name string)

	// UpdateIntervalByName update poll request interval
	UpdateIntervalByName(name string, interval uint64) error

	// UpdateToggleByName update poll request enabled flag
	UpdateToggleByName(name string, toggle bool) error

	// UpdateAllToggles update all poll requests enabled flag
	UpdateAllToggles(toggle bool)
}

IReaderTaskDataStore read task interface

type IWriterTaskDataStore

type IWriterTaskDataStore interface {
	// Add add request to write task map,
	// params: TID, CMD strings.
	Add(tid, cmd string)

	// Get get request from write task map,
	// params: TID string,
	// return: cmd string, exist flag.
	Get(tid string) (string, bool)

	// Delete remove request from write task map
	// params: TID string.
	Delete(tid string)
}

IWriterTaskDataStore write task interface

(Tid, Command) map

type JSONableByteSlice

type JSONableByteSlice []byte

JSONableByteSlice jsonable uint8 array

func (JSONableByteSlice) MarshalJSON

func (u JSONableByteSlice) MarshalJSON() ([]byte, error)

MarshalJSON implements the Marshaler interface on JSONableByteSlice (i.e., uint8/byte array). Ref: http://stackoverflow.com/questions/14177862/how-to-jsonize-a-uint8-slice-in-go

type MbtcpFilterOpReq

type MbtcpFilterOpReq struct {
	Tid     int64  `json:"tid"`
	From    string `json:"from,omitempty"`
	Name    string `json:"name,omitempty"`
	Enabled bool   `json:"enabled,omitempty"`
}

MbtcpFilterOpReq generic modbus tcp filter operation request

type MbtcpFilterStatus

type MbtcpFilterStatus struct {
	Tid     int64      `json:"tid"`
	From    string     `json:"from,omitempty"`
	Name    string     `json:"name"`
	Enabled bool       `json:"enabled"`
	Type    FilterType `json:"type,omitempty"`
	Arg     []float32  `json:"arg,omitempty"`
	Status  string     `json:"status,omitempty"`
}

MbtcpFilterStatus filter status

type MbtcpFiltersStatus

type MbtcpFiltersStatus struct {
	Tid     int64               `json:"tid"`
	From    string              `json:"from,omitempty"`
	Status  string              `json:"status,omitempty"`
	Filters []MbtcpFilterStatus `json:"filters"`
}

MbtcpFiltersStatus requests status

type MbtcpHistoryData

type MbtcpHistoryData struct {
	Tid    int64       `json:"tid"`
	Name   string      `json:"name"`
	Status string      `json:"status"`
	Data   interface{} `json:"history,omitempty"` // universal data container
}

MbtcpHistoryData history data

type MbtcpPollData

type MbtcpPollData struct {
	TimeStamp int64        `json:"ts"`
	Name      string       `json:"name"`
	Status    string       `json:"status"`
	Type      RegValueType `json:"type,omitempty"`
	// Bytes FC3, FC4 and Type 2~8 only
	Bytes JSONableByteSlice `json:"bytes,omitempty"`
	Data  interface{}       `json:"data,omitempty"` // universal data container
}

MbtcpPollData read coil/register response (1.1). `Data interface` supports:

[]uint16, []int16, []uint32, []int32, []float32, string

type MbtcpPollOpReq

type MbtcpPollOpReq struct {
	Tid      int64  `json:"tid"`
	From     string `json:"from,omitempty"`
	Name     string `json:"name,omitempty"`
	Interval uint64 `json:"interval,omitempty"`
	Enabled  bool   `json:"enabled,omitempty"`
}

MbtcpPollOpReq generic modbus tcp poll operation request

type MbtcpPollStatus

type MbtcpPollStatus struct {
	Tid      int64        `json:"tid"`
	From     string       `json:"from,omitempty"`
	Name     string       `json:"name"`
	Interval uint64       `json:"interval"`
	Enabled  bool         `json:"enabled"`
	FC       int          `json:"fc"`
	IP       string       `json:"ip"`
	Port     string       `json:"port,omitempty"`
	Slave    uint8        `json:"slave"`
	Addr     uint16       `json:"addr"`
	Status   string       `json:"status,omitempty"` // 2.3.2 response only
	Len      uint16       `json:"len,omitempty"`
	Type     RegValueType `json:"type,omitempty"`
	Order    Endian       `json:"order,omitempty"`
	Range    *ScaleRange  `json:"range,omitempty"` // point to struct can be omitted in json encode
}

MbtcpPollStatus polling coil/register request;

type MbtcpPollsStatus

type MbtcpPollsStatus struct {
	Tid    int64             `json:"tid"`
	From   string            `json:"from,omitempty"`
	Status string            `json:"status,omitempty"`
	Polls  []MbtcpPollStatus `json:"polls"`
}

MbtcpPollsStatus requests status

type MbtcpReadReq

type MbtcpReadReq struct {
	Tid   int64        `json:"tid"`
	From  string       `json:"from,omitempty"`
	FC    int          `json:"fc"`
	IP    string       `json:"ip"`
	Port  string       `json:"port,omitempty"`
	Slave uint8        `json:"slave"`
	Addr  uint16       `json:"addr"`
	Len   uint16       `json:"len,omitempty"`
	Type  RegValueType `json:"type,omitempty"`
	Order Endian       `json:"order,omitempty"`
	Range *ScaleRange  `json:"range,omitempty"` // point to struct can be omitted in json encode
}

MbtcpReadReq read coil/register request (1.1). Scale range field example:

Range: &ScaleRange{1,2,3,4},

type MbtcpReadRes

type MbtcpReadRes struct {
	Tid    int64        `json:"tid"`
	Status string       `json:"status"`
	Type   RegValueType `json:"type,omitempty"`
	// Bytes FC3, FC4 and Type 2~8 only
	Bytes JSONableByteSlice `json:"bytes,omitempty"`
	Data  interface{}       `json:"data,omitempty"` // universal data container
}

MbtcpReadRes read coil/register response (1.1). `Data interface` supports:

[]uint16, []int16, []uint32, []int32, []float32, string

type MbtcpSimpleRes

type MbtcpSimpleRes struct {
	Tid    int64  `json:"tid"`
	Status string `json:"status"`
}

MbtcpSimpleRes generic modbus tcp response

type MbtcpTimeoutReq

type MbtcpTimeoutReq struct {
	Tid  int64  `json:"tid"`
	From string `json:"from,omitempty"`
	Data int64  `json:"timeout,omitempty"`
}

MbtcpTimeoutReq set/get TCP connection timeout request (1.3, 1.4)

type MbtcpTimeoutRes

type MbtcpTimeoutRes struct {
	Tid    int64  `json:"tid"`
	Status string `json:"status"`
	Data   int64  `json:"timeout,omitempty"`
}

MbtcpTimeoutRes set/get TCP connection timeout response (1.3, 1.4)

type MbtcpWriteReq

type MbtcpWriteReq struct {
	Tid   int64       `json:"tid"`
	From  string      `json:"from,omitempty"`
	FC    int         `json:"fc"`
	IP    string      `json:"ip"`
	Port  string      `json:"port,omitempty"`
	Slave uint8       `json:"slave"`
	Addr  uint16      `json:"addr"`
	Len   uint16      `json:"len,omitempty"`
	Hex   bool        `json:"hex,omitempty"`
	Data  interface{} `json:"data"`
}

MbtcpWriteReq write coil/register request

type ReaderTask

type ReaderTask struct {
	// Name task name
	Name string
	// Cmd zmq frame 1
	Cmd string
	// Req request structure
	Req interface{}
}

ReaderTask read/poll task request

type RegValueType

type RegValueType int

RegValueType return value type defines how to inteprete registers, i.e.,

for modbus read function codes only

const (

	// RegisterArray register array, ex: [12345, 23456, 5678]
	RegisterArray RegValueType
	// HexString hexadecimal string, ex: "112C004F12345678"
	HexString
	// Scale linearly scale
	Scale
	// UInt16 uint16 array
	UInt16
	// Int16 int16 array
	Int16
	// UInt32 uint32 array
	UInt32
	// Int32 int32 array
	Int32
	// Float32 float32 array
	Float32
)

Register value type for read function

type ScaleRange

type ScaleRange struct {
	DomainLow  float64 `json:"a"`
	DomainHigh float64 `json:"b"`
	RangeLow   float64 `json:"c"`
	RangeHigh  float64 `json:"d"`
}

ScaleRange defines scale range