container: remove setup pipe helper

The API forces use of finalizer to close the read end of the setup pipe, which is no longer considered acceptable. Exporting this as part of package container also imposes unnecessary maintenance burden.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/container.go

@@ -53,7 +53,7 @@ type (
 		ExtraFiles []*os.File
 
 		// Write end of a pipe connected to the init to deliver [Params].
-		setup *os.File
+		setup [2]*os.File
 		// Cancels the context passed to the underlying cmd.
 		cancel context.CancelFunc
 		// Closed after Wait returns. Keeps the spawning thread alive.
@@ -287,14 +287,16 @@ func (p *Container) Start() error {
 	}
 
 	// place setup pipe before user supplied extra files, this is later restored by init
-	if fd, f, err := Setup(&p.cmd.ExtraFiles); err != nil {
+	if r, w, err := os.Pipe(); err != nil {
 		return &StartError{
 			Fatal: true,
 			Step:  "set up params stream",
 			Err:   err,
 		}
 	} else {
-		p.setup = f
+		fd := 3 + len(p.cmd.ExtraFiles)
+		p.cmd.ExtraFiles = append(p.cmd.ExtraFiles, r)
+		p.setup[0], p.setup[1] = r, w
 		p.cmd.Env = []string{setupEnv + "=" + strconv.Itoa(fd)}
 	}
 	p.cmd.ExtraFiles = append(p.cmd.ExtraFiles, p.ExtraFiles...)
@@ -428,14 +430,30 @@ func (p *Container) Start() error {
 // Serve serves [Container.Params] to the container init.
 //
 // Serve must only be called once.
-func (p *Container) Serve() error {
-	if p.setup == nil {
+func (p *Container) Serve() (err error) {
+	if p.setup[0] == nil || p.setup[1] == nil {
 		panic("invalid serve")
 	}
+	defer func() {
+		if closeErr := p.setup[1].Close(); err == nil {
+			err = closeErr
+		}
 
-	setup := p.setup
-	p.setup = nil
-	if err := setup.SetDeadline(time.Now().Add(initSetupTimeout)); err != nil {
+		if err != nil {
+			p.cancel()
+		}
+		p.setup[0], p.setup[1] = nil, nil
+	}()
+	if err = p.setup[0].Close(); err != nil {
+		return &StartError{
+			Fatal:       true,
+			Step:        "close read end of init pipe",
+			Err:         err,
+			Passthrough: true,
+		}
+	}
+
+	if err = p.setup[1].SetDeadline(time.Now().Add(initSetupTimeout)); err != nil {
 		return &StartError{
 			Fatal:       true,
 			Step:        "set init pipe deadline",
@@ -445,7 +463,6 @@ func (p *Container) Serve() error {
 	}
 
 	if p.Path == nil {
-		p.cancel()
 		return &StartError{
 			Step:   "invalid executable pathname",
 			Err:    EINVAL,
@@ -461,18 +478,13 @@ func (p *Container) Serve() error {
 		p.SeccompRules = make([]std.NativeRule, 0)
 	}
 
-	err := gob.NewEncoder(setup).Encode(&initParams{
+	return gob.NewEncoder(p.setup[1]).Encode(&initParams{
 		p.Params,
 		Getuid(),
 		Getgid(),
 		len(p.ExtraFiles),
 		p.msg.IsVerbose(),
 	})
-	_ = setup.Close()
-	if err != nil {
-		p.cancel()
-	}
-	return err
 }
 
 // Wait blocks until the container init process to exit and releases any