Add a collector generator script

.gitignore

@@ -1 +1 @@
-/wmi_exporter.exe
+*.exe

tools/collector-generator/New-Collector.ps1

@@ -0,0 +1,18 @@
+Param(
+    [Parameter(Mandatory=$true)]
+    $Class,
+    [Parameter(Mandatory=$false)]
+    $CollectorName = ($Class -replace 'Win32_PerfRawData_Perf','')
+)
+$members = Get-WMIObject $Class `
+    | Get-Member -MemberType Properties `
+    | Where-Object { $_.Definition -Match '^u?int' -and $_.Name -NotMatch '_' } `
+    | Select-Object Name, @{Name="Type";Expression={$_.Definition.Split(" ")[0]}}
+$input = @{
+    "Class"=$Class;
+    "CollectorName"=$CollectorName;
+    "Members"=$members
+} | ConvertTo-Json
+$outFileName = "..\..\collector\$CollectorName.go".ToLower()
+$input | .\collector-generator.exe | Out-File -NoClobber -Encoding UTF8 $outFileName
+go fmt $outFileName

tools/collector-generator/README.md

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+# Collector generator
+Generates a collector skeleton implementation from a WMI class. 
+
+## Usage
+Build the generator:
+
+```bash
+go build .
+```
+
+Run the script to query the WMI service and send the output to the generator:
+
+```powershell
+.\New-Collector.ps1 -Class Win32_PerfRawData_PerfOS_Processor
+```
+
+This will generate a collector. The collector name is generated by first removing `Win32_PerfRawData_Perf` and lower-casing, so `Win32_PerfRawData_PerfOS_Processor` will generate `os_processor.go`. This can be overridden by passing `-CollectorName` to the script.

tools/collector-generator/collector.template

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+// returns data points from {{ .Class }}
+// <add link to documentation here> - {{ .Class }} class
+package collector
+import (
+    "log"
+
+    "github.com/StackExchange/wmi"
+    "github.com/prometheus/client_golang/prometheus"
+)
+func init() {
+    Factories["{{ .CollectorName | toLower }}"] = New{{ .CollectorName }}Collector
+}
+// A {{ .CollectorName }}Collector is a Prometheus collector for WMI {{ .Class }} metrics
+type {{ .CollectorName }}Collector struct {
+{{- range $m := .Members }}
+    {{ $m.Name }} *prometheus.Desc
+{{- end }}
+}
+// New{{ .CollectorName }}Collector ...
+func New{{ .CollectorName }}Collector() (Collector, error) {
+    const subsystem = "{{ .CollectorName | toLower }}"
+    return &{{ .CollectorName }}Collector{
+{{- range $m := .Members }}
+        {{ $m.Name }}: prometheus.NewDesc(
+            prometheus.BuildFQName(Namespace, subsystem, "{{ $m.Name | toSnakeCase }}"),
+            "({{ $m.Name }})",
+            nil,
+            nil,
+        ),
+{{- end }}
+    }, nil
+}
+// Collect sends the metric values for each metric
+// to the provided prometheus Metric channel.
+func (c *{{ .CollectorName }}Collector) Collect(ch chan<- prometheus.Metric) error {
+    if desc, err := c.collect(ch); err != nil {
+        log.Println("[ERROR] failed collecting {{ .CollectorName | toLower }} metrics:", desc, err)
+        return err
+    }
+    return nil
+}
+type {{ .Class }} struct {
+    Name string
+{{ range $m := .Members }}
+    {{ $m.Name }} {{ $m.Type }}
+{{- end }}
+}
+func (c *{{ .CollectorName }}Collector) collect(ch chan<- prometheus.Metric) (*prometheus.Desc, error) {
+    var dst []{{ .Class }}
+    q := wmi.CreateQuery(&dst, "")
+    if err := wmi.Query(q, &dst); err != nil {
+        return nil, err
+    }
+    {{ range $m := .Members }}
+    ch <- prometheus.MustNewConstMetric(
+        c.{{ $m.Name }},
+        prometheus.GaugeValue,
+        float64(dst[0].{{ $m.Name }}),
+    )
+    {{ end }}
+    return nil, nil
+}

tools/collector-generator/generate-collector.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"strings"
+	"text/template"
+	"unicode"
+)
+
+type TemplateData struct {
+	CollectorName string
+	Class         string
+	Members       []Member
+}
+type Member struct {
+	Name string
+	Type string
+}
+
+func main() {
+	bytes, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		panic(err)
+	}
+	var data TemplateData
+	if err := json.Unmarshal(bytes, &data); err != nil {
+		panic(err)
+	}
+
+	funcs := template.FuncMap{
+		"toLower":     strings.ToLower,
+		"toSnakeCase": toSnakeCase,
+	}
+	template, err := template.New("template").Funcs(funcs).ParseFiles("collector.template")
+	if err != nil {
+		panic(err)
+	}
+	err = template.ExecuteTemplate(os.Stdout, "collector.template", data)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// https://gist.github.com/elwinar/14e1e897fdbe4d3432e1
+func toSnakeCase(in string) string {
+	runes := []rune(in)
+	length := len(runes)
+
+	var out []rune
+	for i := 0; i < length; i++ {
+		if i > 0 && unicode.IsUpper(runes[i]) && ((i+1 < length && unicode.IsLower(runes[i+1])) || unicode.IsLower(runes[i-1])) {
+			out = append(out, '_')
+		}
+		out = append(out, unicode.ToLower(runes[i]))
+	}
+
+	return string(out)
+}