netwatch/backend/cmd/netwatch-server/main_test.go

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"net"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"testing"
	"time"
)

// The tests run main() in a child process, this test binary started
// again with runMainEnv set, because main() can exit its process and
// takes its settings from the environment.
const runMainEnv = "NETWATCH_SERVER_RUN_MAIN"

// childTimeout bounds each child's whole run; it is killed after it.
const childTimeout = 10 * time.Second

func TestMain(m *testing.M) {
	if os.Getenv(runMainEnv) != "" {
		// A SIGTERM that comes before fx catches it is dropped, not fatal.
		signal.Notify(make(chan os.Signal, 1), syscall.SIGTERM)
		main()

		return
	}

	os.Exit(m.Run())
}

// TestOutputIsJSON: off a terminal, every line the server writes from
// start to stop is JSON, fx's own lines included.
func TestOutputIsJSON(t *testing.T) {
	t.Parallel()

	ctx, cancel := context.WithTimeout(t.Context(), childTimeout)
	defer cancel()

	port := freePort(ctx, t)
	child, stdout, stderr := startServer(ctx, t, t.TempDir(), port)

	waitForHealthcheck(ctx, t, port)

	// The child drops a SIGTERM that comes before fx catches it (see
	// TestMain), so send one every 100ms until the test ends. ctx
	// bounds the wait: when it ends, the child is killed.
	stop := make(chan struct{})
	defer close(stop)

	go func() {
		for {
			_ = child.Process.Signal(syscall.SIGTERM)

			select {
			case <-stop:
				return
			case <-time.After(100 * time.Millisecond):
			}
		}
	}()

	err := child.Wait()
	if err != nil {
		t.Fatalf("server exit = %v, want success", err)
	}

	requireJSONLines(t, stdout, stderr)

	if !strings.Contains(stdout.String(), `"msg":"starting"`) {
		t.Fatalf("no startup line in stdout:\n%s", stdout)
	}
}

// TestMalformedConfigFileStopsTheStart: a config file the server finds
// but cannot read stops the start, and the error is logged as JSON.
func TestMalformedConfigFileStopsTheStart(t *testing.T) {
	t.Parallel()

	ctx, cancel := context.WithTimeout(t.Context(), childTimeout)
	defer cancel()

	home := t.TempDir()
	dir := filepath.Join(home, ".config", "netwatch-server")

	err := os.MkdirAll(dir, 0o750)
	if err != nil {
		t.Fatal(err)
	}

	err = os.WriteFile(filepath.Join(dir, "netwatch-server.yaml"),
		[]byte("PORT: [8080\n"), 0o600)
	if err != nil {
		t.Fatal(err)
	}

	child, stdout, stderr := startServer(ctx, t, home, freePort(ctx, t))

	err = child.Wait()
	if child.ProcessState.ExitCode() != 1 {
		t.Fatalf("server exit = %v, want exit status 1", err)
	}

	requireJSONLines(t, stdout, stderr)

	if !strings.Contains(stdout.String(), "netwatch-server.yaml") {
		t.Fatalf("no error naming the config file in stdout:\n%s", stdout)
	}
}

// startServer runs main() in a child process listening on
// 127.0.0.1:port, with home as its HOME and working directory and its
// data directory in home, so it touches nothing outside home. Its
// stdout and stderr go to the two buffers returned, which hold all of
// it once child.Wait returns. The child is killed when ctx ends, and
// killed and reaped when the test ends if nothing waited for it.
func startServer(
	ctx context.Context,
	t *testing.T,
	home, port string,
) (*exec.Cmd, *bytes.Buffer, *bytes.Buffer) {
	t.Helper()

	self, err := os.Executable()
	if err != nil {
		t.Fatal(err)
	}

	var stdout, stderr bytes.Buffer

	child := exec.CommandContext(ctx, self) //nolint:gosec // this test binary
	child.Dir = home
	child.Env = append(os.Environ(),
		runMainEnv+"=1",
		"HOME="+home,
		"DATA_DIR="+filepath.Join(home, "data"),
		"BIND_ADDRESS=127.0.0.1",
		"PORT="+port,
	)
	child.Stdout = &stdout
	child.Stderr = &stderr

	err = child.Start()
	if err != nil {
		t.Fatal(err)
	}

	t.Cleanup(func() {
		if child.ProcessState == nil {
			_ = child.Process.Kill()
			_ = child.Wait()
		}
	})

	return child, &stdout, &stderr
}

// freePort returns a TCP port on 127.0.0.1 that was free a moment ago.
func freePort(ctx context.Context, t *testing.T) string {
	t.Helper()

	var lc net.ListenConfig

	l, err := lc.Listen(ctx, "tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}

	_ = l.Close()

	_, port, err := net.SplitHostPort(l.Addr().String())
	if err != nil {
		t.Fatal(err)
	}

	return port
}

// waitForHealthcheck returns once the health check on port answers 200.
func waitForHealthcheck(ctx context.Context, t *testing.T, port string) {
	t.Helper()

	url := "http://127.0.0.1:" + port + "/.well-known/healthcheck"

	for {
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
		if err != nil {
			t.Fatal(err)
		}

		resp, err := http.DefaultClient.Do(req)
		if err == nil {
			_ = resp.Body.Close()

			if resp.StatusCode == http.StatusOK {
				return
			}
		}

		select {
		case <-ctx.Done():
			t.Fatalf("health check never answered: %v", err)
		case <-time.After(50 * time.Millisecond):
		}
	}
}

// requireJSONLines fails the test on each line of outs that is not
// JSON.
func requireJSONLines(t *testing.T, outs ...*bytes.Buffer) {
	t.Helper()

	for _, out := range outs {
		for line := range strings.Lines(out.String()) {
			if !json.Valid([]byte(line)) {
				t.Errorf("line is not JSON: %s", line)
			}
		}
	}
}