memory: fix panics if metrics does not exists (#1960)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

cmd/windows_exporter/main_test.go

@@ -0,0 +1,188 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/windows"
+)
+
+//nolint:tparallel
+func TestRun(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name            string
+		args            []string
+		config          string
+		metricsEndpoint string
+		exitCode        int
+	}{
+		{
+			name:            "default",
+			args:            []string{},
+			metricsEndpoint: "http://127.0.0.1:9182/metrics",
+		},
+		{
+			name:            "web.listen-address",
+			args:            []string{"--web.listen-address=127.0.0.1:8080"},
+			metricsEndpoint: "http://127.0.0.1:8080/metrics",
+		},
+		{
+			name:            "web.listen-address",
+			args:            []string{"--web.listen-address=127.0.0.1:8081", "--web.listen-address=[::1]:8081"},
+			metricsEndpoint: "http://[::1]:8081/metrics",
+		},
+		{
+			name:            "config",
+			args:            []string{"--config.file=config.yaml"},
+			config:          `{"web":{"listen-address":"127.0.0.1:8082"}}`,
+			metricsEndpoint: "http://127.0.0.1:8082/metrics",
+		},
+		{
+			name:            "web.listen-address with config",
+			args:            []string{"--config.file=config.yaml", "--web.listen-address=127.0.0.1:8084"},
+			config:          `{"web":{"listen-address":"127.0.0.1:8083"}}`,
+			metricsEndpoint: "http://127.0.0.1:8084/metrics",
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx, cancel := context.WithCancel(t.Context())
+			defer cancel()
+
+			if tc.config != "" {
+				// Create a temporary config file.
+				tmpfile, err := os.CreateTemp(t.TempDir(), "config-*.yaml")
+				require.NoError(t, err)
+
+				t.Cleanup(func() {
+					require.NoError(t, tmpfile.Close())
+				})
+
+				_, err = tmpfile.WriteString(tc.config)
+				require.NoError(t, err)
+
+				for i, arg := range tc.args {
+					tc.args[i] = strings.ReplaceAll(arg, "config.yaml", tmpfile.Name())
+				}
+			}
+
+			exitCodeCh := make(chan int)
+
+			var stdout string
+
+			go func() {
+				stdout = captureOutput(t, func() {
+					// Simulate the service control manager signaling that we are done.
+					exitCodeCh <- run(ctx, tc.args)
+				})
+			}()
+
+			t.Cleanup(func() {
+				select {
+				case exitCode := <-exitCodeCh:
+					require.Equal(t, tc.exitCode, exitCode)
+				case <-time.After(2 * time.Second):
+					t.Fatalf("timed out waiting for exit code, want %d", tc.exitCode)
+				}
+			})
+
+			if tc.exitCode != 0 {
+				return
+			}
+
+			uri, err := url.Parse(tc.metricsEndpoint)
+			require.NoError(t, err)
+
+			err = waitUntilListening(t, "tcp", uri.Host)
+			require.NoError(t, err, "LOGS:\n%s", stdout)
+
+			req, err := http.NewRequestWithContext(ctx, http.MethodGet, tc.metricsEndpoint, nil)
+			require.NoError(t, err)
+
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err, "LOGS:\n%s", stdout)
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+
+			body, err := io.ReadAll(resp.Body)
+			require.NoError(t, err)
+
+			err = resp.Body.Close()
+			require.NoError(t, err)
+
+			require.NotEmpty(t, body)
+			require.Contains(t, string(body), "# HELP windows_exporter_build_info")
+
+			cancel()
+		})
+	}
+}
+
+func captureOutput(tb testing.TB, f func()) string {
+	tb.Helper()
+
+	orig := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+
+	f()
+
+	os.Stdout = orig
+
+	_ = w.Close()
+
+	out, _ := io.ReadAll(r)
+
+	return string(out)
+}
+
+func waitUntilListening(tb testing.TB, network, address string) error {
+	tb.Helper()
+
+	var (
+		conn net.Conn
+		err  error
+	)
+
+	for range 10 {
+		conn, err = net.DialTimeout(network, address, 100*time.Millisecond)
+		if err == nil {
+			_ = conn.Close()
+
+			return nil
+		}
+
+		if errors.Is(err, windows.Errno(10061)) {
+			time.Sleep(50 * time.Millisecond)
+
+			continue
+		}
+	}
+
+	return fmt.Errorf("listener not listening: %w", err)
+}