WIP: implemented Ping, implemented Set and Shutdown in agent, and added umask

service/serve.go

@@ -19,9 +19,12 @@ limitations under the License.
 import (
 	"context"
 	"fmt"
+	"golang.org/x/sys/unix"
 	"net"
 	"os"
+	"os/exec"
 	"sync/atomic"
+	"syscall"
 	"time"
 
 	pb "gitea.suyono.dev/suyono/go-agent/proto"
@@ -32,8 +35,12 @@ import (
 
 type Option interface {
 	SocketPath() string
-	Expiry() string
 	StopGraceTime() time.Duration
+	Background() bool
+	ExecArgs() []string
+	ExecEnv() []string
+	ExecLogPath() string
+	Umask() int
 }
 
 type Storage interface {
@@ -42,6 +49,18 @@ type Storage interface {
 	Shutdown() error
 }
 
+type BgProcFlag int
+
+const (
+	child BgProcFlag = iota
+	parent
+)
+
+const (
+	goAgentDaemonEnvFlag = "GO_AGENT_DAEMON"
+	goAgentDaemonLogPath = "GO_AGENT_DAEMON_LOG"
+)
+
 type server struct {
 	pb.UnimplementedAgentServer
 	stor Storage
@@ -77,6 +96,48 @@ func (s *server) Shutdown(context.Context, *emptypb.Empty) (*emptypb.Empty, erro
 	return &emptypb.Empty{}, nil
 }
 
+func GetDaemonLogPath() (string, error) {
+	// The child process of the main program should call this function and set up the logging infrastructure
+	envVal, ok := os.LookupEnv(goAgentDaemonLogPath)
+	if !ok {
+		return "", fmt.Errorf("programming issue: parent process did not set log path")
+	}
+	return envVal, nil
+}
+
+func ExecBackground(opt Option) (BgProcFlag, error) {
+	var (
+		cmd    *exec.Cmd
+		ok     bool
+		envVal string
+	)
+
+	args := opt.ExecArgs()
+	envVal, ok = os.LookupEnv(goAgentDaemonEnvFlag)
+	if !opt.Background() || len(args) == 0 || (envVal == "1" && ok) {
+		return child, nil
+	}
+
+	if len(args) > 1 {
+		cmd = exec.Command(args[0], args[1:]...)
+	} else {
+		cmd = exec.Command(args[0])
+	}
+	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=1", goAgentDaemonEnvFlag))
+	if opt.ExecLogPath() != "" {
+		cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", goAgentDaemonLogPath, opt.ExecLogPath()))
+	}
+	cmd.Env = append(cmd.Env, opt.ExecEnv()...)
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = nil, nil, nil
+
+	if err := cmd.Start(); err != nil {
+		return parent, err
+	}
+
+	return parent, nil
+}
+
 func Serve(ctx context.Context, opt Option) error {
 	var (
 		l      net.Listener
@@ -85,18 +146,30 @@ func Serve(ctx context.Context, opt Option) error {
 		ok     bool
 		sw     *atomic.Bool
 		cancel context.CancelFunc
+		bgFlag BgProcFlag
 	)
-	socketPath := opt.SocketPath()
-	os.Remove(socketPath)
 
-	if l, err = net.Listen("unix", socketPath); err != nil {
-		return fmt.Errorf("failed to listen on unix socket: %w", err)
+	if bgFlag, err = ExecBackground(opt); err != nil {
+		return fmt.Errorf("could not start background process: %w", err)
+	}
+	if bgFlag == parent {
+		return nil
 	}
 
+	_ = os.Remove(opt.SocketPath())
+
+	oldUmask := unix.Umask(opt.Umask())
+	if l, err = net.Listen("unix", opt.SocketPath()); err != nil {
+		return fmt.Errorf("failed to listen on unix socket: %w", err)
+	}
+	unix.Umask(oldUmask)
+
 	grpcServer := grpc.NewServer()
-	pb.RegisterAgentServer(grpcServer, &server{stor: storage.NewInMap()})
-	errChan := make(chan error, 1)
 	ctx, cancel = context.WithCancel(ctx)
+	pb.RegisterAgentServer(grpcServer, &server{
+		stor: storage.NewInMap(cancel),
+	})
+	errChan := make(chan error, 1)
 	sw = new(atomic.Bool)
 	sw.Store(false)
 
@@ -137,3 +210,7 @@ fsl:
 
 	return err
 }
+
+func (s *server) Ping(ctx context.Context, req *emptypb.Empty) (*emptypb.Empty, error) {
+	return &emptypb.Empty{}, nil
+}