Continue scrape with duplicated metrics

Problems of a single collector, like duplicated metrics read via the
textfile collector, should not fail the collection and export of other
metrics.

node_exporter_test.go

@@ -2,21 +2,23 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"testing"
 	"time"
 
 	"github.com/prometheus/procfs"
 )
 
-func TestFileDescriptorLeak(t *testing.T) {
-	const (
-		binary  = "./node_exporter"
-		address = "localhost:9100"
-	)
+const (
+	binary  = "./node_exporter"
+	address = "localhost:19100"
+)
 
+func TestFileDescriptorLeak(t *testing.T) {
 	if _, err := os.Stat(binary); err != nil {
 		t.Skipf("node_exporter binary not available, try to run `make build` first: %s", err)
 	}
@@ -24,75 +26,111 @@ func TestFileDescriptorLeak(t *testing.T) {
 		t.Skipf("proc filesystem is not available, but currently required to read number of open file descriptors: %s", err)
 	}
 
-	errc := make(chan error)
 	exporter := exec.Command(binary, "-web.listen-address", address)
-	go func() {
-		if err := exporter.Run(); err != nil {
-			errc <- fmt.Errorf("execution of node_exporter failed: %s", err)
-		} else {
-			errc <- nil
-		}
-	}()
-
-	select {
-	case err := <-errc:
-		t.Fatal(err)
-	case <-time.After(100 * time.Millisecond):
-	}
-
-	go func(pid int, url string) {
-		if err := queryExporter(url); err != nil {
-			errc <- err
-			return
+	test := func(pid int) error {
+		if err := queryExporter(address); err != nil {
+			return err
 		}
 		proc, err := procfs.NewProc(pid)
 		if err != nil {
-			errc <- err
-			return
+			return err
 		}
 		fdsBefore, err := proc.FileDescriptors()
 		if err != nil {
-			errc <- err
-			return
+			return err
 		}
 		for i := 0; i < 5; i++ {
-			if err := queryExporter(url); err != nil {
-				errc <- err
-				return
+			if err := queryExporter(address); err != nil {
+				return err
 			}
 		}
 		fdsAfter, err := proc.FileDescriptors()
 		if err != nil {
-			errc <- err
-			return
+			return err
 		}
 		if want, have := len(fdsBefore), len(fdsAfter); want != have {
-			errc <- fmt.Errorf("want %d open file descriptors after metrics scrape, have %d", want, have)
+			return fmt.Errorf("want %d open file descriptors after metrics scrape, have %d", want, have)
 		}
-		errc <- nil
-	}(exporter.Process.Pid, fmt.Sprintf("http://%s/metrics", address))
+		return nil
+	}
 
-	select {
-	case err := <-errc:
-		if exporter.Process != nil {
-			exporter.Process.Kill()
-		}
-		if err != nil {
-			t.Fatal(err)
-		}
+	if err := runCommandAndTests(exporter, test); err != nil {
+		t.Error(err)
 	}
 }
 
-func queryExporter(url string) error {
-	resp, err := http.Get(url)
+func TestHandlingOfDuplicatedMetrics(t *testing.T) {
+	if _, err := os.Stat(binary); err != nil {
+		t.Skipf("node_exporter binary not available, try to run `make build` first: %s", err)
+	}
+
+	dir, err := ioutil.TempDir("", "node-exporter")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	content := []byte("dummy_metric 1\n")
+	if err := ioutil.WriteFile(filepath.Join(dir, "a.prom"), content, 0600); err != nil {
+		t.Fatal(err)
+	}
+	if err := ioutil.WriteFile(filepath.Join(dir, "b.prom"), content, 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	exporter := exec.Command(binary, "-web.listen-address", address, "-collector.textfile.directory", dir)
+	test := func(_ int) error {
+		return queryExporter(address)
+	}
+
+	if err := runCommandAndTests(exporter, test); err != nil {
+		t.Error(err)
+	}
+}
+
+func queryExporter(address string) error {
+	resp, err := http.Get(fmt.Sprintf("http://%s/metrics", address))
 	if err != nil {
 		return err
 	}
 	if err := resp.Body.Close(); err != nil {
 		return err
 	}
-	if want, have := resp.StatusCode, http.StatusOK; want != have {
+	if want, have := http.StatusOK, resp.StatusCode; want != have {
 		return fmt.Errorf("want /metrics status code %d, have %d", want, have)
 	}
 	return nil
 }
+
+func runCommandAndTests(cmd *exec.Cmd, fn func(pid int) error) error {
+	errc := make(chan error)
+	go func() {
+		if err := cmd.Run(); err != nil {
+			errc <- fmt.Errorf("execution of command failed: %s", err)
+		} else {
+			errc <- nil
+		}
+	}()
+
+	// Allow the process to start before running any tests.
+	select {
+	case err := <-errc:
+		return err
+	case <-time.After(100 * time.Millisecond):
+	}
+
+	go func(pid int) {
+		errc <- fn(pid)
+	}(cmd.Process.Pid)
+
+	select {
+	case err := <-errc:
+		if cmd.Process != nil {
+			cmd.Process.Kill()
+		}
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}