libimage: pull: increase timeout running under systemd

Set the `EXTEND_TIMEOUT_USEC` over DBUS when pulling an image from a
registry and when running under systemd.  This will prevent a frequent
issue when running Quadlets and exceeding the default systemd start
timeout of 90 seconds when pulling the image takes too long.

Fixes: containers/podman/issues/18353
Signed-off-by: Valentin Rothberg <[email protected]>

libimage/pull.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net"
+	"os"
 	"runtime"
 	"strings"
 	"time"
@@ -592,6 +594,62 @@ func (r *Runtime) copySingleImageFromRegistry(ctx context.Context, imageName str
 		return nil
 	}
 
+	// Avoid running out of time when running inside a systemd unit by
+	// regularly increasing the timeout.
+	if socketPath, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
+		socketAddr := &net.UnixAddr{
+			Name: socketPath,
+			Net:  "unixgram",
+		}
+		conn, err := net.DialUnix(socketAddr.Net, nil, socketAddr)
+		if err != nil {
+			return nil, err
+		}
+		defer conn.Close()
+
+		numExtensions := 10
+		extension := 30 * time.Second
+		timerFrequency := 25 * time.Second // Fire the timer at a higher frequency to avoid a race
+		timer := time.NewTimer(timerFrequency)
+		socketCtx, cancel := context.WithCancel(ctx)
+		defer cancel()
+		defer timer.Stop()
+
+		logrus.Warnf("Pulling image %s inside systemd: setting pull timeout to %s", imageName, time.Duration(numExtensions)*extension)
+
+		// From `man systemd.service(5)`:
+		//
+		// "If a service of Type=notify/Type=notify-reload sends "EXTEND_TIMEOUT_USEC=...", this may cause
+		// the start time to be extended beyond TimeoutStartSec=. The first receipt of this message must
+		// occur before TimeoutStartSec= is exceeded, and once the start time has extended beyond
+		// TimeoutStartSec=, the service manager will allow the service to continue to start, provided the
+		// service repeats "EXTEND_TIMEOUT_USEC=..."  within the interval specified until the service startup
+		// status is finished by "READY=1"."
+		extendValue := []byte(fmt.Sprintf("EXTEND_TIMEOUT_USEC=%d", extension.Microseconds()))
+		extendTimeout := func() {
+			if _, err := conn.Write(extendValue); err != nil {
+				logrus.Errorf("Increasing EXTEND_TIMEOUT_USEC failed: %v", err)
+			}
+			numExtensions--
+		}
+
+		extendTimeout()
+		go func() {
+			for {
+				select {
+				case <-socketCtx.Done():
+					return
+				case <-timer.C:
+					if numExtensions == 0 {
+						return
+					}
+					extendTimeout()
+					timer.Reset(extension)
+				}
+			}
+		}()
+	}
+
 	c, err := r.newCopier(&options.CopyOptions)
 	if err != nil {
 		return nil, err