cmd: Implement sd_notify() to notify systemd about readiness (#3963)

Issue: #3786
Based on Gaurav Dhameeja's work in #3908.

cmd/commandfuncs.go

@@ -271,6 +271,10 @@ func cmdRun(fl Flags) (int, error) {
 		}
 	}
 
+	if err := NotifyReadiness(); err != nil {
+		caddy.Log().Error("unable to notify readiness to service manager", zap.Error(err))
+	}
+
 	select {}
 }
 
@@ -291,6 +295,15 @@ func cmdReload(fl Flags) (int, error) {
 	reloadCmdConfigAdapterFlag := fl.String("adapter")
 	reloadCmdAddrFlag := fl.String("address")
 
+	if err := NotifyReloading(); err != nil {
+		caddy.Log().Error("unable to notify reloading to service manager", zap.Error(err))
+	}
+	defer func() {
+		if err := NotifyReadiness(); err != nil {
+			caddy.Log().Error("unable to notify readiness to service manager", zap.Error(err))
+		}
+	}()
+
 	// get the config in caddy's native format
 	config, configFile, err := loadConfig(reloadCmdConfigFlag, reloadCmdConfigAdapterFlag)
 	if err != nil {

cmd/notify.go

@@ -0,0 +1,23 @@
+// Copyright 2015 Matthew Holt and The Caddy 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.
+
+package caddycmd
+
+func NotifyReadiness() error {
+	return notifyReadiness()
+}
+
+func NotifyReloading() error {
+	return notifyReloading()
+}

cmd/notify_linux.go

@@ -0,0 +1,68 @@
+// Copyright 2015 Matthew Holt and The Caddy 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.
+
+package caddycmd
+
+import (
+	"io"
+	"net"
+	"os"
+	"strings"
+)
+
+// The documentation about this IPC protocol is available here:
+// https://www.freedesktop.org/software/systemd/man/sd_notify.html
+
+func sdNotify(path, payload string) error {
+	socketAddr := &net.UnixAddr{
+		Name: path,
+		Net:  "unixgram",
+	}
+
+	conn, err := net.DialUnix(socketAddr.Net, nil, socketAddr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	if _, err := io.Copy(conn, strings.NewReader(payload)); err != nil {
+		return err
+	}
+	return nil
+}
+
+// notifyReadiness notifies systemd caddy that has finished its
+// initialization routines.
+func notifyReadiness() error {
+	val, ok := os.LookupEnv("NOTIFY_SOCKET")
+	if !ok || val == "" {
+		return nil
+	}
+	if err := sdNotify(val, "READY=1"); err != nil {
+		return err
+	}
+	return nil
+}
+
+// notifyReadiness notifies systemd that caddy is reloading its config.
+func notifyReloading() error {
+	val, ok := os.LookupEnv("NOTIFY_SOCKET")
+	if !ok || val == "" {
+		return nil
+	}
+	if err := sdNotify(val, "RELOADING=1"); err != nil {
+		return err
+	}
+	return nil
+}

cmd/notify_other.go

@@ -0,0 +1,25 @@
+// Copyright 2015 Matthew Holt and The Caddy 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.
+
+// +build !linux
+
+package caddycmd
+
+func notifyReadiness() error {
+	return nil
+}
+
+func notifyReloading() error {
+	return nil
+}