From a203370aaad15513296f53f7ad2285836bedb9ad Mon Sep 17 00:00:00 2001
From: Thomas Gruber <Thomas.Roehl@googlemail.com>
Date: Fri, 25 Feb 2022 14:46:29 +0100
Subject: [PATCH] Add scraper for Prometheus clients (#47)

---
 receivers/prometheusReceiver.go | 122 ++++++++++++++++++++++++++++++++
 receivers/prometheusReceiver.md |  27 +++++++
 2 files changed, 149 insertions(+)
 create mode 100644 receivers/prometheusReceiver.go
 create mode 100644 receivers/prometheusReceiver.md

diff --git a/receivers/prometheusReceiver.go b/receivers/prometheusReceiver.go
new file mode 100644
index 0000000..c22969d
--- /dev/null
+++ b/receivers/prometheusReceiver.go
@@ -0,0 +1,122 @@
+package receivers
+
+import (
+	"bufio"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	cclog "github.com/ClusterCockpit/cc-metric-collector/internal/ccLogger"
+	lp "github.com/ClusterCockpit/cc-metric-collector/internal/ccMetric"
+)
+
+type PrometheusReceiverConfig struct {
+	defaultReceiverConfig
+	Addr     string `json:"address"`
+	Port     string `json:"port"`
+	Path     string `json:"path"`
+	Interval string `json:"interval"`
+	SSL      bool   `json:"ssl"`
+}
+
+type PrometheusReceiver struct {
+	receiver
+	meta     map[string]string
+	config   PrometheusReceiverConfig
+	interval time.Duration
+	done     chan bool
+	wg       sync.WaitGroup
+	ticker   *time.Ticker
+	uri      string
+}
+
+func (r *PrometheusReceiver) Start() {
+	cclog.ComponentDebug(r.name, "START", r.uri)
+	r.wg.Add(1)
+
+	r.ticker = time.NewTicker(r.interval)
+	go func() {
+		for {
+			select {
+			case <-r.done:
+				r.wg.Done()
+				return
+			case t := <-r.ticker.C:
+				resp, err := http.Get(r.uri)
+				if err != nil {
+					log.Fatal(err)
+				}
+				defer resp.Body.Close()
+
+				scanner := bufio.NewScanner(resp.Body)
+				for scanner.Scan() {
+					line := scanner.Text()
+					if strings.HasPrefix(line, "#") {
+						continue
+					}
+					lineSplit := strings.Fields(line)
+					// separate metric name from tags (labels in Prometheus)
+					tags := map[string]string{}
+					name := lineSplit[0]
+					if sindex := strings.Index(name, "{"); sindex >= 0 {
+						eindex := strings.Index(name, "}")
+						for _, kv := range strings.Split(name[sindex+1:eindex], ",") {
+							eq := strings.Index(kv, "=")
+							tags[kv[0:eq]] = strings.Trim(kv[eq+1:], "\"")
+						}
+						name = lineSplit[0][0:sindex]
+					}
+					value, err := strconv.ParseFloat(lineSplit[1], 64)
+					if err == nil {
+						y, err := lp.New(name, tags, r.meta, map[string]interface{}{"value": value}, t)
+						if err == nil {
+							r.sink <- y
+						}
+					}
+				}
+			}
+		}
+	}()
+}
+
+func (r *PrometheusReceiver) Close() {
+	cclog.ComponentDebug(r.name, "CLOSE")
+	r.done <- true
+	r.wg.Wait()
+}
+
+func NewPrometheusReceiver(name string, config json.RawMessage) (Receiver, error) {
+	r := new(PrometheusReceiver)
+	r.name = fmt.Sprintf("PrometheusReceiver(%s)", name)
+	if len(config) > 0 {
+		err := json.Unmarshal(config, &r.config)
+		if err != nil {
+			cclog.ComponentError(r.name, "Error reading config:", err.Error())
+			return nil, err
+		}
+	}
+	if len(r.config.Addr) == 0 ||
+		len(r.config.Port) == 0 ||
+		len(r.config.Interval) == 0 {
+		return nil, errors.New("not all configuration variables set required by PrometheusReceiver (address and port)")
+	}
+	if len(r.config.Interval) > 0 {
+		t, err := time.ParseDuration(r.config.Interval)
+		if err == nil {
+			r.interval = t
+		}
+	}
+	r.meta = map[string]string{"source": r.name}
+	proto := "http"
+	if r.config.SSL {
+		proto = "https"
+	}
+	r.uri = fmt.Sprintf("%s://%s:%s/%s", proto, r.config.Addr, r.config.Port, r.config.Path)
+	return r, nil
+}
diff --git a/receivers/prometheusReceiver.md b/receivers/prometheusReceiver.md
new file mode 100644
index 0000000..5fe6e46
--- /dev/null
+++ b/receivers/prometheusReceiver.md
@@ -0,0 +1,27 @@
+## `prometheus` receiver
+
+The `prometheus` receiver can be used to scrape the metrics of a single `prometheus` client. It does **not** use any official Golang library but making simple HTTP get requests and parse the response.
+
+### Configuration structure
+
+```json
+{
+  "<name>": {
+    "type": "prometheus",
+    "address" : "testpromhost",
+    "port" : "12345",
+    "port" : "/prometheus",
+    "interval": "5s",
+    "ssl" : true,
+  }
+}
+```
+
+- `type`: makes the receiver a `prometheus` receiver
+- `address`: Hostname or IP of the Prometheus agent
+- `port`: Port of Prometheus agent
+- `path`: Path to the Prometheus endpoint
+- `interval`: Scrape the Prometheus endpoint in this interval (default '5s')
+- `ssl`: Use SSL or not
+
+The receiver requests data from `http(s)://<address>:<port>/<path>`.
\ No newline at end of file