From 001f768b8bcafd640dd69f72503c708a89ebac1c Mon Sep 17 00:00:00 2001
From: "m.nabokikh" <maksim.nabokikh@flant.com>
Date: Wed, 30 Oct 2019 02:49:19 +0400
Subject: [PATCH] Add ability to scrape and listen unix domain sockets

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>
---
 exporter.go | 63 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 58 insertions(+), 5 deletions(-)

diff --git a/exporter.go b/exporter.go
index 30629da70..4afa6fa89 100644
--- a/exporter.go
+++ b/exporter.go
@@ -1,14 +1,17 @@
 package main
 
 import (
+	"context"
 	"crypto/tls"
 	"flag"
 	"fmt"
 	"log"
+	"net"
 	"net/http"
 	"os"
 	"os/signal"
 	"strconv"
+	"strings"
 	"syscall"
 	"time"
 
@@ -110,6 +113,42 @@ func createClientWithRetries(getClient func() (interface{}, error), retries uint
 	return nil, err
 }
 
+func parseUnixSocketAddress(listenAddress string) (string, string, error) {
+	listenAddressParts := strings.Split(listenAddress, ":")
+	listenAddressPartsLength := len(listenAddressParts)
+
+	if listenAddressPartsLength > 3 || listenAddressPartsLength < 1 {
+		return "", "", fmt.Errorf("address for unix domain socket has wrong format")
+	}
+
+	unixSocketPath := listenAddressParts[1]
+	requestPath := ""
+	if listenAddressPartsLength == 2 {
+		requestPath = listenAddressParts[2]
+	}
+	return unixSocketPath, requestPath, nil
+}
+
+func startListeningOn(listenAddress string) error {
+	if !strings.HasPrefix(listenAddress, "unix:") {
+		return http.ListenAndServe(listenAddress, nil)
+	}
+	path, _, err := parseUnixSocketAddress(listenAddress)
+	if err != nil {
+		log.Fatalf("parsing unix domain socket listen address %s failed: %+v", listenAddress, err)
+	}
+	listener, err := net.ListenUnix("unix", &net.UnixAddr{Name: path, Net: "unix"})
+	if err != nil {
+		log.Fatalf("binding to unix domain socket listen address %s failed: %+v", path, err)
+	}
+
+	err = os.Chmod(path, 0777)
+	if err != nil {
+		log.Printf("changing access rules of unix domain socket %s failed: %+v", path, err)
+	}
+	return http.Serve(listener, nil)
+}
+
 var (
 	// Set during go build
 	version   string
@@ -177,11 +216,25 @@ func main() {
 
 	registry.MustRegister(buildInfoMetric)
 
+	transport := &http.Transport{
+		TLSClientConfig: &tls.Config{InsecureSkipVerify: !*sslVerify},
+	}
+	if strings.HasPrefix(*scrapeURI, "unix:") {
+		socketPath, requestPath, err := parseUnixSocketAddress(*scrapeURI)
+		if err != nil {
+			log.Fatalf("parsing unix domain socket scrape address %s failed: %+v", *scrapeURI, err)
+		}
+
+		transport.DialContext = func(_ context.Context, _, _ string) (net.Conn, error) {
+			return net.Dial("unix", socketPath)
+		}
+		newScrapeURI := "http://unix" + requestPath
+		scrapeURI = &newScrapeURI
+	}
+
 	httpClient := &http.Client{
-		Timeout: timeout.Duration,
-		Transport: &http.Transport{
-			TLSClientConfig: &tls.Config{InsecureSkipVerify: !*sslVerify},
-		},
+		Timeout:   timeout.Duration,
+		Transport: transport,
 	}
 
 	signalChan := make(chan os.Signal, 1)
@@ -222,5 +275,5 @@ func main() {
 		}
 	})
 	log.Printf("NGINX Prometheus Exporter has successfully started")
-	log.Fatal(http.ListenAndServe(*listenAddr, nil))
+	log.Fatal(startListeningOn(*listenAddr))
 }