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Thomas Roehl 2022-03-15 15:43:53 +01:00
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MIT License
Copyright (c) 2021 ClusterCockpit
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

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# ccUnits - A unit system for ClusterCockpit
When working with metrics, the problem comes up that they may use different unit name but have the same unit in fact. There are a lot of real world examples like 'kB' and 'Kbyte'. In CC Metric Collector, the Collectors read data from different sources which may use different units or the programmer specifies a unit for a metric by hand. The ccUnits system is not comparable with the SI unit system. If you are looking for a package for the SI units, see [here](https://pkg.go.dev/github.com/gurre/si).
In order to enable unit comparison and conversion, the ccUnits package provides some helpers:
There are basically two important functions:
```go
NewUnit(unit string) Unit
GetUnitPrefixFactor(in Unit, out Unit) (func(value float64) float64, error) // Get conversion function for the value
type Unit interface {
Valid() bool
String() string
Short() string
AddDivisorUnit(div Measure)
}
```
In order to get the "normalized" string unit back or test for validity, you can use:
```go
u := NewUnit("MB")
fmt.Println(u.Valid()) // true
fmt.Printf("Long string %q", u.String()) // MegaBytes
fmt.Printf("Short string %q", u.Short()) // MBytes
v := NewUnit("foo")
fmt.Println(v.Valid()) // false
```
If you have two units and need the conversion function:
```go
u1 := NewUnit("kB")
u2 := NewUnit("MBytes")
convFunc, err := GetUnitPrefixFactor(u1, u2) // Returns an error if the units have different measures
if err == nil {
v2 := convFunc(v1)
}
```
(In the ClusterCockpit ecosystem the separation between values and units if useful since they are commonly not stored as a single entity but the value is a field in the CCMetric while unit is a tag or a meta information).
If you have a metric and want the derivation to a bandwidth or events per second, you can use the original unit:
```go
in_unit, err := metric.GetMeta("unit")
if err == nil {
value, ok := metric.GetField("value")
if ok {
out_unit = NewUnit(in_unit)
out_unit.AddDivisorUnit("seconds")
seconds := timeDiff.Seconds()
y, err := lp.New(metric.Name()+"_bw",
metric.Tags(),
metric.Meta(),
map[string]interface{"value": value/seconds},
metric.Time())
if err == nil {
y.AddMeta("unit", out_unit.Short())
}
}
}
```
## Special unit detection
Some used measures like Bytes and Flops are non-dividable. Consequently there prefixes like Milli, Micro and Nano are not useful. This is quite handy since a unit `mb` for `MBytes` is not uncommon but would by default be parsed as "MilliBytes".
Special parsing rules for the following measures: iff `prefix==Milli`, use `prefix==Mega`
- `Bytes`
- `Flops`
- `Packets`
- `Events`
- `Cycles`
- `Requests`
This means the prefixes `Micro` (like `ubytes`) and `Nano` like (`nflops/sec`) are not allowed and return an invalid unit. But you can specify `mflops` and `mb`.
Prefixes for `%` or `percent` are ignored.
## Supported prefixes
```go
const (
Base Prefix = iota
Exa = 1e18
Peta = 1e15
Tera = 1e12
Giga = 1e9
Mega = 1e6
Kilo = 1e3
Milli = 1e-3
Micro = 1e-6
Nano = 1e-9
Kibi = 1024
Mebi = 1024 * 1024
Gibi = 1024 * 1024 * 1024
Tebi = 1024 * 1024 * 1024 * 1024
)
```
The prefixes are detected using a regular expression `^([kKmMgGtTpP]?[i]?)(.*)` that splits the prefix from the measure. You probably don't need to deal with the prefixes in the code.
## Supported measures
```go
const (
None Measure = iota
Bytes
Flops
Percentage
TemperatureC
TemperatureF
Rotation
Hertz
Time
Watt
Joule
Cycles
Requests
Packets
Events
)
```
There a regular expression for each of the measures like `^([bB][yY]?[tT]?[eE]?[sS]?)` for the `Bytes` measure.
## New units
If the selected units are not suitable for your metric, feel free to send a PR.
### New prefix
For a new prefix, add it to the big `const` in `ccUnitPrefix.go` and adjust the prefix-unit-splitting regular expression. Afterwards, you have to add cases to the three functions `String()`, `Prefix()` and `NewPrefix()`. `NewPrefix()` contains the parser (`k` or `K` -> `Kilo`). The other one are used for output. `String()` outputs a longer version of the prefix (`Kilo`), while `Prefix()` returns only the short notation (`K`).
### New measure
Adding new prefixes is probably rare but adding a new measure is a more common task. At first, add it to the big `const` in `ccUnitMeasure.go`. Moreover, create a regular expression matching the measure (and pre-compile it like the others). Add the expression matching to `NewMeasure()`. The `String()` and `Short()` functions return descriptive strings for the measure in long form (like `Hertz`) and short form (like `Hz`).
If there are special conversation rules between measures and you want to convert one measure to another, like temperatures in Celsius to Fahrenheit, a special case in `GetUnitPrefixFactor()` is required.
### Special parsing rules
The two parsers for prefix and measure are called under the hood by `NewUnit()` and there might some special rules apply. Like in the above section about 'special unit detection', special rules for your new measure might be required. Currently there are two special cases:
- Measures that are non-dividable like Flops, Bytes, Events, ... cannot use `Milli`, `Micro` and `Nano`. The prefix `m` is forced to `M` for these measures
- If the prefix is `p`/`P` (`Peta`) or `e`/`E` (`Exa`) and the measure is not detectable, it retries detection with the prefix. So first round it tries, for example, prefix `p` and measure `ackets` which fails, so it retries the detection with measure `packets` and `<empty>` prefix (resolves to `Base` prefix).
## Limitations
The `ccUnits` package is a simple implemtation of a unit system and comes with some limitations:
- The unit denominator (like `s` in `Mbyte/s`) can only have the `Base` prefix, you cannot specify `Byte/ms` for "Bytes per milli second".

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package ccunits
import "regexp"
type Measure int
const (
None Measure = iota
Bytes
Flops
Percentage
TemperatureC
TemperatureF
Rotation
Hertz
Time
Watt
Joule
Cycles
Requests
Packets
Events
)
func (m *Measure) String() string {
switch *m {
case Bytes:
return "Bytes"
case Flops:
return "Flops"
case Percentage:
return "Percent"
case TemperatureC:
return "DegreeC"
case TemperatureF:
return "DegreeF"
case Rotation:
return "RPM"
case Hertz:
return "Hertz"
case Time:
return "Seconds"
case Watt:
return "Watts"
case Joule:
return "Joules"
case Cycles:
return "Cycles"
case Requests:
return "Requests"
case Packets:
return "Packets"
case Events:
return "Events"
default:
return "Unknown"
}
}
func (m *Measure) Short() string {
switch *m {
case Bytes:
return "Bytes"
case Flops:
return "Flops"
case Percentage:
return "Percent"
case TemperatureC:
return "degC"
case TemperatureF:
return "degF"
case Rotation:
return "RPM"
case Hertz:
return "Hz"
case Time:
return "s"
case Watt:
return "W"
case Joule:
return "J"
case Cycles:
return "cyc"
case Requests:
return "requests"
case Packets:
return "packets"
case Events:
return "events"
default:
return "Unknown"
}
}
const bytesRegexStr = `^([bB][yY]?[tT]?[eE]?[sS]?)`
const flopsRegexStr = `^([fF][lL]?[oO]?[pP]?[sS]?)`
const percentRegexStr = `^(%|[pP]ercent)`
const degreeCRegexStr = `^(deg[Cc]|°[cC])`
const degreeFRegexStr = `^(deg[fF]|°[fF])`
const rpmRegexStr = `^([rR][pP][mM])`
const hertzRegexStr = `^([hH][eE]?[rR]?[tT]?[zZ])`
const timeRegexStr = `^([sS][eE]?[cC]?[oO]?[nN]?[dD]?[sS]?)`
const wattRegexStr = `^([wW][aA]?[tT]?[tT]?[sS]?)`
const jouleRegexStr = `^([jJ][oO]?[uU]?[lL]?[eE]?[sS]?)`
const cyclesRegexStr = `^([cC][yY][cC]?[lL]?[eE]?[sS]?)`
const requestsRegexStr = `^([rR][eE][qQ][uU]?[eE]?[sS]?[tT]?[sS]?)`
const packetsRegexStr = `^([pP][aA]?[cC]?[kK][eE]?[tT][sS]?)`
const eventsRegexStr = `^([eE][vV]?[eE]?[nN][tT][sS]?)`
var bytesRegex = regexp.MustCompile(bytesRegexStr)
var flopsRegex = regexp.MustCompile(flopsRegexStr)
var percentRegex = regexp.MustCompile(percentRegexStr)
var degreeCRegex = regexp.MustCompile(degreeCRegexStr)
var degreeFRegex = regexp.MustCompile(degreeFRegexStr)
var rpmRegex = regexp.MustCompile(rpmRegexStr)
var hertzRegex = regexp.MustCompile(hertzRegexStr)
var timeRegex = regexp.MustCompile(timeRegexStr)
var wattRegex = regexp.MustCompile(wattRegexStr)
var jouleRegex = regexp.MustCompile(jouleRegexStr)
var cyclesRegex = regexp.MustCompile(cyclesRegexStr)
var requestsRegex = regexp.MustCompile(requestsRegexStr)
var packetsRegex = regexp.MustCompile(packetsRegexStr)
var eventsRegex = regexp.MustCompile(eventsRegexStr)
func NewMeasure(unit string) Measure {
var match []string
match = bytesRegex.FindStringSubmatch(unit)
if match != nil {
return Bytes
}
match = flopsRegex.FindStringSubmatch(unit)
if match != nil {
return Flops
}
match = percentRegex.FindStringSubmatch(unit)
if match != nil {
return Percentage
}
match = degreeCRegex.FindStringSubmatch(unit)
if match != nil {
return TemperatureC
}
match = degreeFRegex.FindStringSubmatch(unit)
if match != nil {
return TemperatureF
}
match = rpmRegex.FindStringSubmatch(unit)
if match != nil {
return Rotation
}
match = hertzRegex.FindStringSubmatch(unit)
if match != nil {
return Hertz
}
match = timeRegex.FindStringSubmatch(unit)
if match != nil {
return Time
}
match = cyclesRegex.FindStringSubmatch(unit)
if match != nil {
return Cycles
}
match = wattRegex.FindStringSubmatch(unit)
if match != nil {
return Watt
}
match = jouleRegex.FindStringSubmatch(unit)
if match != nil {
return Joule
}
match = requestsRegex.FindStringSubmatch(unit)
if match != nil {
return Requests
}
match = packetsRegex.FindStringSubmatch(unit)
if match != nil {
return Packets
}
match = eventsRegex.FindStringSubmatch(unit)
if match != nil {
return Events
}
return None
}

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package ccunits
import "regexp"
type Prefix float64
const (
Base Prefix = 1
Exa = 1e18
Peta = 1e15
Tera = 1e12
Giga = 1e9
Mega = 1e6
Kilo = 1e3
Milli = 1e-3
Micro = 1e-6
Nano = 1e-9
Kibi = 1024
Mebi = 1024 * 1024
Gibi = 1024 * 1024 * 1024
Tebi = 1024 * 1024 * 1024 * 1024
)
const prefixRegexStr = `^([kKmMgGtTpP]?[i]?)(.*)`
var prefixRegex = regexp.MustCompile(prefixRegexStr)
func (s *Prefix) String() string {
switch *s {
case Base:
return ""
case Kilo:
return "Kilo"
case Mega:
return "Mega"
case Giga:
return "Giga"
case Tera:
return "Tera"
case Peta:
return "Peta"
case Exa:
return "Exa"
case Milli:
return "Milli"
case Micro:
return "Micro"
case Nano:
return "Nano"
case Kibi:
return "Kibi"
case Mebi:
return "Mebi"
case Gibi:
return "Gibi"
case Tebi:
return "Tebi"
default:
return "Unkn"
}
}
func (s *Prefix) Prefix() string {
switch *s {
case Base:
return ""
case Kilo:
return "K"
case Mega:
return "M"
case Giga:
return "G"
case Tera:
return "T"
case Peta:
return "P"
case Exa:
return "E"
case Milli:
return "m"
case Micro:
return "u"
case Nano:
return "n"
case Kibi:
return "Ki"
case Mebi:
return "Mi"
case Gibi:
return "Gi"
case Tebi:
return "Ti"
default:
return "<unkn>"
}
}
func NewPrefix(prefix string) Prefix {
switch prefix {
case "k":
return Kilo
case "K":
return Kilo
case "m":
return Milli
case "M":
return Mega
case "g":
return Giga
case "G":
return Giga
case "t":
return Tera
case "T":
return Tera
case "p":
return Peta
case "P":
return Peta
case "e":
return Exa
case "E":
return Exa
case "u":
return Micro
case "n":
return Nano
case "ki":
return Kibi
case "Ki":
return Kibi
case "Mi":
return Mebi
case "gi":
return Gibi
case "Gi":
return Gibi
case "Ti":
return Tebi
case "":
return Base
default:
return Base
}
}

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package ccunits
import (
"fmt"
"strings"
)
type unit struct {
prefix Prefix
measure Measure
divMeasure Measure
}
type Unit interface {
Valid() bool
String() string
Short() string
AddDivisorUnit(div Measure)
getPrefix() Prefix
getMeasure() Measure
getDivMeasure() Measure
}
func (u *unit) Valid() bool {
return u.measure != None
}
func (u *unit) String() string {
if u.divMeasure != None {
return fmt.Sprintf("%s%s/%s", u.prefix.String(), u.measure.String(), u.divMeasure.String())
} else {
return fmt.Sprintf("%s%s", u.prefix.String(), u.measure.String())
}
}
func (u *unit) Short() string {
if u.divMeasure != None {
return fmt.Sprintf("%s%s/%s", u.prefix.Prefix(), u.measure.Short(), u.divMeasure.Short())
} else {
return fmt.Sprintf("%s%s", u.prefix.Prefix(), u.measure.Short())
}
}
func (u *unit) AddDivisorUnit(div Measure) {
u.divMeasure = div
}
func (u *unit) getPrefix() Prefix {
return u.prefix
}
func (u *unit) getMeasure() Measure {
return u.measure
}
func (u *unit) getDivMeasure() Measure {
return u.divMeasure
}
func GetPrefixFactor(in Prefix, out Prefix) func(value float64) float64 {
var factor = 1.0
var in_prefix = float64(in)
var out_prefix = float64(out)
factor = in_prefix / out_prefix
return func(value float64) float64 { return factor }
}
func GetUnitPrefixFactor(in Unit, out Unit) (func(value float64) float64, error) {
if in.getMeasure() == TemperatureC && out.getMeasure() == TemperatureF {
return func(value float64) float64 { return (value * 1.8) + 32 }, nil
} else if in.getMeasure() == TemperatureF && out.getMeasure() == TemperatureC {
return func(value float64) float64 { return (value - 32) / 1.8 }, nil
} else if in.getMeasure() != out.getMeasure() || in.getDivMeasure() != out.getDivMeasure() {
return func(value float64) float64 { return 1.0 }, fmt.Errorf("invalid measures in in and out Unit")
}
return GetPrefixFactor(in.getPrefix(), out.getPrefix()), nil
}
func NewUnit(unitStr string) Unit {
u := &unit{
prefix: Base,
measure: None,
divMeasure: None,
}
matches := prefixRegex.FindStringSubmatch(unitStr)
if len(matches) > 2 {
pre := NewPrefix(matches[1])
measures := strings.Split(matches[2], "/")
m := NewMeasure(measures[0])
// Special case for prefix 'p' or 'P' (Peta) and measures starting with 'p' or 'P'
// like 'packets' or 'percent'. Same for 'e' or 'E' (Exa) for measures starting with
// 'e' or 'E' like 'events'
if m == None {
switch pre {
case Peta, Exa:
t := NewMeasure(matches[1] + measures[0])
if t != None {
m = t
pre = Base
}
}
}
div := None
if len(measures) > 1 {
div = NewMeasure(measures[1])
}
switch m {
// Special case for 'm' as prefix for Bytes and some others as thers is no unit like MilliBytes
case Bytes, Flops, Packets, Events, Cycles, Requests:
if pre == Milli {
pre = Mega
}
// Special case for percentage. No/ignore prefix
case Percentage:
pre = Base
}
u.prefix = pre
u.measure = m
u.divMeasure = div
}
return u
}

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package ccunits
import (
"fmt"
"testing"
)
func TestUnitsExact(t *testing.T) {
testCases := []struct {
in string
want Unit
}{
{"b", NewUnit("Bytes")},
{"B", NewUnit("Bytes")},
{"byte", NewUnit("Bytes")},
{"bytes", NewUnit("Bytes")},
{"BYtes", NewUnit("Bytes")},
{"Mb", NewUnit("MBytes")},
{"MB", NewUnit("MBytes")},
{"Mbyte", NewUnit("MBytes")},
{"Mbytes", NewUnit("MBytes")},
{"MbYtes", NewUnit("MBytes")},
{"Gb", NewUnit("GBytes")},
{"GB", NewUnit("GBytes")},
{"Hz", NewUnit("Hertz")},
{"MHz", NewUnit("MHertz")},
{"GHertz", NewUnit("GHertz")},
{"pkts", NewUnit("Packets")},
{"packets", NewUnit("Packets")},
{"packet", NewUnit("Packets")},
{"flop", NewUnit("Flops")},
{"flops", NewUnit("Flops")},
{"floPS", NewUnit("Flops")},
{"Mflop", NewUnit("MFlops")},
{"Gflop", NewUnit("GFlops")},
{"gflop", NewUnit("GFlops")},
{"%", NewUnit("Percent")},
{"percent", NewUnit("Percent")},
{"degc", NewUnit("degC")},
{"degC", NewUnit("degC")},
{"degf", NewUnit("degF")},
{"°f", NewUnit("degF")},
{"events", NewUnit("events")},
{"event", NewUnit("events")},
{"EveNts", NewUnit("events")},
{"reqs", NewUnit("requests")},
{"requests", NewUnit("requests")},
{"Requests", NewUnit("requests")},
{"cyc", NewUnit("cycles")},
{"cy", NewUnit("cycles")},
{"Cycles", NewUnit("cycles")},
{"J", NewUnit("Joules")},
{"Joule", NewUnit("Joules")},
{"joule", NewUnit("Joules")},
{"W", NewUnit("Watt")},
{"Watts", NewUnit("Watt")},
{"watt", NewUnit("Watt")},
{"s", NewUnit("seconds")},
{"sec", NewUnit("seconds")},
{"secs", NewUnit("seconds")},
{"RPM", NewUnit("rpm")},
{"rPm", NewUnit("rpm")},
{"watt/byte", NewUnit("W/B")},
{"watts/bytes", NewUnit("W/B")},
{"flop/byte", NewUnit("flops/Bytes")},
{"F/B", NewUnit("flops/Bytes")},
}
compareUnitExact := func(in, out Unit) bool {
if in.getMeasure() == out.getMeasure() && in.getDivMeasure() == out.getDivMeasure() && in.getPrefix() == out.getPrefix() {
return true
}
return false
}
for _, c := range testCases {
u := NewUnit(c.in)
if (!u.Valid()) || (!compareUnitExact(u, c.want)) {
t.Errorf("func NewUnit(%q) == %q, want %q", c.in, u.String(), c.want.String())
}
}
}
func TestUnitsDifferentPrefix(t *testing.T) {
testCases := []struct {
in string
want Unit
prefixFactor float64
}{
{"kb", NewUnit("Bytes"), 1000},
{"Mb", NewUnit("Bytes"), 1000000},
{"Mb/s", NewUnit("Bytes/s"), 1000000},
{"Flops/s", NewUnit("MFlops/s"), 1e-6},
{"Flops/s", NewUnit("GFlops/s"), 1e-9},
{"MHz", NewUnit("Hertz"), 1e6},
{"kb", NewUnit("Kib"), 1000.0 / 1024},
{"Mib", NewUnit("MBytes"), (1024 * 1024.0) / (1e6)},
{"mb", NewUnit("MBytes"), 1.0},
}
compareUnitWithPrefix := func(in, out Unit, factor float64) bool {
if in.getMeasure() == out.getMeasure() && in.getDivMeasure() == out.getDivMeasure() {
if f := GetPrefixFactor(in.getPrefix(), out.getPrefix()); f(1.0) == factor {
return true
} else {
fmt.Println(f(1.0))
}
}
return false
}
for _, c := range testCases {
u := NewUnit(c.in)
if (!u.Valid()) || (!compareUnitWithPrefix(u, c.want, c.prefixFactor)) {
t.Errorf("func NewUnit(%q) == %q, want %q with factor %f", c.in, u.String(), c.want.String(), c.prefixFactor)
}
}
}