init

Dockerfile

@@ -0,0 +1,14 @@
+FROM golang:1.15 as build
+
+ADD . /app
+WORKDIR /app
+ENV GOOS=linux
+ENV CGO_ENABLED=0
+RUN go build .
+
+# ---
+
+FROM busybox
+
+COPY --from=build /app/viewercount /usr/local/bin/viewercount
+CMD /usr/local/bin/viewercount

go.mod

@@ -0,0 +1,3 @@
+module foosinn/viewercount
+
+go 1.15

main.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"regexp"
+	"strconv"
+
+	"net/http"
+)
+
+const COUNTER_SLOTS = 20
+
+func main() {
+	counter := NewCounter()
+	go counter.ScanStdin()
+
+	http.HandleFunc("/", counter.MetricsHandler)
+	err := http.ListenAndServe(":8080", nil)
+	log.Fatalf("unable to listen: %s", err)
+}
+
+type Counter struct {
+	counters []int
+	names    []string
+	current  int
+}
+
+func NewCounter() *Counter {
+	return &Counter{
+		counters: make([]int, COUNTER_SLOTS),
+		names:    make([]string, COUNTER_SLOTS),
+	}
+}
+
+func (c *Counter) MetricsHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Add("Content-Type", "text/plain")
+	for i, name := range c.names {
+		fmt.Fprintf(w, "rc3_stream_count[name=%q] %d\n", name, c.counters[i])
+	}
+	fmt.Fprintf(w, "rc3_stream_current[name=\"%d\"] 1\n", c.current)
+}
+
+func (c *Counter) ScanStdin() {
+	matcher := regexp.MustCompile(`/hls/stream-([0-9]*).ts`)
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Split(bufio.ScanLines)
+
+	for scanner.Scan() {
+		matches := matcher.FindStringSubmatch(scanner.Text())
+		if len(matches) == 2 {
+			c.countViewers(matches[1])
+		}
+	}
+}
+
+func (c *Counter) countViewers(part string) {
+	i, _ := strconv.Atoi(part)
+	mod := i % COUNTER_SLOTS
+
+	if c.names[mod] != part {
+		c.counters[mod] = 0
+	}
+	c.current = i
+	c.counters[mod] += 1
+	c.names[mod] = part
+}