Implement systemd notification support after all templates have been …

…rendered (#1794)

* Reopening PR, request to add feature systemd notify on runner

* Change the directory structure

manager/runner.go

@@ -20,6 +20,7 @@ import (
 	"github.com/hashicorp/consul-template/config"
 	dep "github.com/hashicorp/consul-template/dependency"
 	"github.com/hashicorp/consul-template/renderer"
+	"github.com/hashicorp/consul-template/systemd"
 	"github.com/hashicorp/consul-template/template"
 	"github.com/hashicorp/consul-template/watch"
 
@@ -32,6 +33,10 @@ const (
 	viewLimit = 128
 )
 
+type notifier interface {
+	Notify(string) error
+}
+
 // Runner responsible rendering Templates and invoking Commands.
 type Runner struct {
 	// ErrCh and DoneCh are channels where errors and finish notifications occur.
@@ -108,6 +113,12 @@ type Runner struct {
 	// NOTE this is only used when CT is being used as a library.
 	Env map[string]string
 
+	// notifier is called after all templates have been successfully rendered
+	notifier notifier
+
+	// ready indicates that the runner has rendered each template at least once
+	ready bool
+
 	// stopLock is the lock around checking if the runner can be stopped
 	stopLock sync.Mutex
 
@@ -377,6 +388,13 @@ func (r *Runner) Start() {
 				r.Stop()
 				return
 			}
+
+			if r.notifier != nil && !r.ready {
+				if notifErr := r.notifier.Notify(systemd.Ready); notifErr != nil {
+					log.Printf("[DEBUG] (runner) systemd notify failed: %v", notifErr)
+				}
+			}
+			r.ready = true
 		}
 
 	OUTER:
@@ -1000,6 +1018,9 @@ func (r *Runner) init(clients *dep.ClientSet) error {
 		}
 	}
 
+	r.notifier = &systemd.Notifier{}
+	r.ready = false
+
 	return nil
 }
 

manager/runner_test.go

@@ -6,6 +6,7 @@ package manager
 import (
 	"bytes"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -20,6 +21,13 @@ import (
 	"github.com/hashicorp/consul-template/template"
 )
 
+type mockNotifier struct{ s string }
+
+func (n *mockNotifier) Notify(state string) error {
+	n.s = state
+	return nil
+}
+
 func TestRunner_initTemplates(t *testing.T) {
 	c := config.TestConfig(
 		&config.Config{
@@ -549,6 +557,51 @@ func TestRunner_Start(t *testing.T) {
 		}
 	})
 
+	t.Run("notify", func(t *testing.T) {
+		t.Parallel()
+
+		out, err := ioutil.TempFile("", "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer os.Remove(out.Name())
+
+		c := config.DefaultConfig().Merge(&config.Config{
+			Templates: &config.TemplateConfigs{
+				&config.TemplateConfig{
+					Contents:    config.String(`test`),
+					Destination: config.String(out.Name()),
+				},
+			},
+		})
+		c.Finalize()
+
+		r, err := NewRunner(c, false)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		notify := &mockNotifier{}
+		r.notifier = notify
+
+		go r.Start()
+		defer r.Stop()
+
+		select {
+		case err := <-r.ErrCh:
+			t.Fatal(err)
+		case <-r.renderedCh:
+			if !r.ready {
+				t.Errorf("\nexp: %#v\nact: %#v", true, r.ready)
+			}
+			if exp, act := "READY=1", notify.s; exp != act {
+				t.Errorf("\nexp: %#v\nact: %#v", exp, act)
+			}
+		case <-time.After(2 * time.Second):
+			t.Fatal("timeout")
+		}
+	})
+
 	t.Run("run_no_deps", func(t *testing.T) {
 		out, err := os.CreateTemp("", "")
 		if err != nil {

systemd/notifier.go

@@ -0,0 +1,35 @@
+package systemd
+
+import (
+	"errors"
+	"net"
+	"os"
+)
+
+var errNoSocket = errors.New("no socket")
+
+const Ready = "READY=1"
+
+// Notifier provides a method to send a message to systemd.
+type Notifier struct{}
+
+// Notify sends a message to the init daemon. It is common to ignore the error.
+func (n *Notifier) Notify(state string) error {
+	addr := &net.UnixAddr{
+		Name: os.Getenv("NOTIFY_SOCKET"),
+		Net:  "unixgram",
+	}
+
+	if addr.Name == "" {
+		return errNoSocket
+	}
+
+	conn, err := net.DialUnix(addr.Net, nil, addr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	_, err = conn.Write([]byte(state))
+	return err
+}