commit 8502019852557047d7ffcc5d8b52424c9693876c
Author: Sergiusz Bazanski <q3k@q3k.org>
Date:   Thu Aug 30 13:51:08 2018 +0100

    gunwokod

diff --git a/main.go b/main.go
new file mode 100644
index 0000000..62f0904
--- /dev/null
+++ b/main.go
@@ -0,0 +1,226 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/golang/glog"
+	"golang.org/x/net/html"
+)
+
+var (
+	flagLuftdaten      string
+	flagScrapeInterval int
+	flagListen         string
+)
+
+func init() {
+	flag.Set("logtostderr", "true")
+}
+
+type sensorData struct {
+	// Whether the data is fresh.
+	stale bool
+	// PM2.5 in ug/m3
+	pm25 float64
+	// PM10 in ug/m3
+	pm10 float64
+	// Temperature in degrees centigrade
+	temperature float64
+	// Humidity in percent
+	humidity float64
+}
+
+func getSensorData() (sensorData, error) {
+	data := sensorData{}
+
+	resp, err := http.Get(flagLuftdaten)
+	if err != nil {
+		return data, fmt.Errorf("when GETing data: %v", err)
+	}
+
+	root, err := html.Parse(resp.Body)
+	if err != nil {
+		return data, fmt.Errorf("when parsing HTML: %v", err)
+	}
+
+	// Find html.
+	htmlN := root.FirstChild
+	if htmlN == nil || htmlN.Type != html.ElementNode || htmlN.Data != "html" {
+		return data, fmt.Errorf("unexpected root node")
+	}
+	// Find body.
+	bodyN := htmlN.FirstChild.NextSibling
+	if bodyN == nil || bodyN.Type != html.ElementNode || bodyN.Data != "body" {
+		return data, fmt.Errorf("unexpected html[1] node")
+	}
+	// Find div class=content
+	contentN := bodyN.FirstChild.NextSibling
+	if contentN == nil || contentN.Type != html.ElementNode || contentN.Data != "div" || contentN.Attr[0].Key != "class" || contentN.Attr[0].Val != "content" {
+		return data, fmt.Errorf("unexpected body[1] node")
+	}
+	// Find table.
+	var tableN *html.Node = nil
+	for c := contentN.FirstChild; c != nil; c = c.NextSibling {
+		if c.Type == html.ElementNode && c.Data == "table" {
+			tableN = c
+			break
+		}
+	}
+	if tableN == nil {
+		return data, fmt.Errorf("could not find table")
+	}
+	// Find tbody.
+	tbodyN := tableN.FirstChild
+	if tbodyN == nil || tbodyN.Type != html.ElementNode || tbodyN.Data != "tbody" {
+		return data, fmt.Errorf("unexpected table[0] node")
+	}
+
+	got := make(map[string]bool)
+	// Iterate throught rows.
+	for row := tbodyN.FirstChild; row != nil; row = row.NextSibling {
+		td1 := row.FirstChild
+		if td1 == nil {
+			continue
+		}
+		td2 := td1.NextSibling
+		if td2 == nil {
+			continue
+		}
+		td3 := td2.NextSibling
+		if td3 == nil {
+			continue
+		}
+		if td1.Data != "td" || td2.Data != "td" || td3.Data != "td" {
+			continue
+		}
+
+		if td2.FirstChild.Data == "PM2.5" {
+			// This is not an ASCII space.
+			parts := strings.Split(td3.FirstChild.Data, " ")
+			if len(parts) != 2 {
+				continue
+			}
+			pm25, err := strconv.ParseFloat(parts[0], 64)
+			if err != nil {
+				continue
+			}
+			data.pm25 = pm25
+			got["PM2.5"] = true
+		}
+		if td2.FirstChild.Data == "PM10" {
+			// This is not an ASCII space.
+			parts := strings.Split(td3.FirstChild.Data, " ")
+			if len(parts) != 2 {
+				continue
+			}
+			pm10, err := strconv.ParseFloat(parts[0], 64)
+			if err != nil {
+				continue
+			}
+			data.pm10 = pm10
+			got["PM10"] = true
+		}
+		if td2.FirstChild.Data == "Temperatur" {
+			// This is not an ASCII space.
+			parts := strings.Split(td3.FirstChild.Data, " ")
+			if len(parts) != 2 {
+				continue
+			}
+			temp, err := strconv.ParseFloat(parts[0], 64)
+			if err != nil {
+				continue
+			}
+			data.temperature = temp
+			got["Temperature"] = true
+		}
+		if td2.FirstChild.Data == "rel. Luftfeuchte" {
+			// This is not an ASCII space.
+			parts := strings.Split(td3.FirstChild.Data, " ")
+			if len(parts) != 2 {
+				continue
+			}
+			hum, err := strconv.ParseFloat(parts[0], 64)
+			if err != nil {
+				continue
+			}
+			data.humidity = hum
+			got["Humidity"] = true
+		}
+	}
+
+	for _, want := range []string{"PM2.5", "PM10", "Temperature", "Humidity"} {
+		if !got[want] {
+			return data, fmt.Errorf("could not find %v in HTML", want)
+		}
+	}
+	return data, nil
+}
+
+func scraper(req chan int, resp chan sensorData) error {
+	data := sensorData{
+		stale: true,
+	}
+
+	feed := func() {
+		newData, err := getSensorData()
+		if err != nil {
+			glog.Error("Could not get sensor data: %v", err)
+			data.stale = true
+		} else {
+			data = newData
+			glog.Errorf("Got sensor data: %f/%f/%f/%f", data.pm25, data.pm10, data.temperature, data.humidity)
+		}
+	}
+
+	feed()
+
+	ticker := time.NewTicker(time.Duration(flagScrapeInterval) * time.Second)
+	for {
+		select {
+		case <-req:
+			resp <- data
+		case <-ticker.C:
+			feed()
+		}
+	}
+}
+
+func main() {
+	flag.StringVar(&flagLuftdaten, "luftdaten", "http://127.0.0.1:2140/values", "Luftdaten sensor endpoint")
+	flag.IntVar(&flagScrapeInterval, "scrape_interval", 60, "Scrape interval of Luftdaten, in seconds")
+	flag.StringVar(&flagListen, "listen", "0.0.0.0:2141", "Address to listen at for Prometheus requests")
+	flag.Parse()
+
+	glog.Info("Starting scraper...")
+	req := make(chan int, 1)
+	res := make(chan sensorData, 1)
+	go scraper(req, res)
+
+	http.HandleFunc("/metrics", func(w http.ResponseWriter, r *http.Request) {
+		req <- 0
+		data := <-res
+		if data.stale {
+			fmt.Fprintf(w, "# data is stale :(\n")
+			return
+		}
+
+		fmt.Fprintf(w, "# HELP pm25 The current PM2.5 concentration in micrograms per cubic meter\n")
+		fmt.Fprintf(w, "# TYPE pm25 gauge\n")
+		fmt.Fprintf(w, "pm25 %f\n", data.pm25)
+		fmt.Fprintf(w, "# HELP pm10 The current PM10 concentration in micrograms per cubic meter\n")
+		fmt.Fprintf(w, "# TYPE pm10 gauge\n")
+		fmt.Fprintf(w, "pm10 %f\n", data.pm10)
+		fmt.Fprintf(w, "# HELP temperature The current temperature in degrees centigrate\n")
+		fmt.Fprintf(w, "# TYPE temperature gauge\n")
+		fmt.Fprintf(w, "temperature %f\n", data.temperature)
+		fmt.Fprintf(w, "# HELP humidity The current relative humidity in percent\n")
+		fmt.Fprintf(w, "# TYPE humidity gauge\n")
+		fmt.Fprintf(w, "humidity %f\n", data.humidity)
+	})
+	http.ListenAndServe(flagListen, nil)
+}