container/params: expose pipe

This increases flexibility of how caller wants to handle the I/O. Also makes it no longer rely on finalizer.

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

container/container.go

@@ -25,6 +25,9 @@ const (
 	// CancelSignal is the signal expected by container init on context cancel.
 	// A custom [Container.Cancel] function must eventually deliver this signal.
 	CancelSignal = SIGUSR2
+
+	// Timeout for writing initParams to Container.setup.
+	initSetupTimeout = 5 * time.Second
 )
 
 type (
@@ -37,8 +40,8 @@ type (
 		// with behaviour identical to its [exec.Cmd] counterpart.
 		ExtraFiles []*os.File
 
-		// param encoder for shim and init
-		setup *gob.Encoder
+		// param pipe for shim and init
+		setup *os.File
 		// cancels cmd
 		cancel context.CancelFunc
 		// closed after Wait returns
@@ -228,10 +231,10 @@ func (p *Container) Start() error {
 	}
 
 	// place setup pipe before user supplied extra files, this is later restored by init
-	if fd, e, err := Setup(&p.cmd.ExtraFiles); err != nil {
+	if fd, f, err := Setup(&p.cmd.ExtraFiles); err != nil {
 		return &StartError{true, "set up params stream", err, false, false}
 	} else {
-		p.setup = e
+		p.setup = f
 		p.cmd.Env = []string{setupEnv + "=" + strconv.Itoa(fd)}
 	}
 	p.cmd.ExtraFiles = append(p.cmd.ExtraFiles, p.ExtraFiles...)
@@ -310,6 +313,9 @@ func (p *Container) Serve() error {
 
 	setup := p.setup
 	p.setup = nil
+	if err := setup.SetDeadline(time.Now().Add(initSetupTimeout)); err != nil {
+		return &StartError{true, "set init pipe deadline", err, false, true}
+	}
 
 	if p.Path == nil {
 		p.cancel()
@@ -324,15 +330,14 @@ func (p *Container) Serve() error {
 		p.SeccompRules = make([]seccomp.NativeRule, 0)
 	}
 
-	err := setup.Encode(
-		&initParams{
-			p.Params,
-			Getuid(),
-			Getgid(),
-			len(p.ExtraFiles),
-			p.msg.IsVerbose(),
-		},
-	)
+	err := gob.NewEncoder(setup).Encode(&initParams{
+		p.Params,
+		Getuid(),
+		Getgid(),
+		len(p.ExtraFiles),
+		p.msg.IsVerbose(),
+	})
+	_ = setup.Close()
 	if err != nil {
 		p.cancel()
 	}

container/params.go

@@ -9,13 +9,13 @@ import (
 )
 
 // Setup appends the read end of a pipe for setup params transmission and returns its fd.
-func Setup(extraFiles *[]*os.File) (int, *gob.Encoder, error) {
+func Setup(extraFiles *[]*os.File) (int, *os.File, error) {
 	if r, w, err := os.Pipe(); err != nil {
 		return -1, nil, err
 	} else {
 		fd := 3 + len(*extraFiles)
 		*extraFiles = append(*extraFiles, r)
-		return fd, gob.NewEncoder(w), nil
+		return fd, w, nil
 	}
 }
 

container/params_test.go

@@ -1,6 +1,7 @@
 package container_test
 
 import (
+	"encoding/gob"
 	"errors"
 	"os"
 	"slices"
@@ -59,12 +60,16 @@ func TestSetupReceive(t *testing.T) {
 
 			encoderDone := make(chan error, 1)
 			extraFiles := make([]*os.File, 0, 1)
-			if fd, encoder, err := container.Setup(&extraFiles); err != nil {
+			deadline, _ := t.Deadline()
+			if fd, f, err := container.Setup(&extraFiles); err != nil {
 				t.Fatalf("Setup: error = %v", err)
 			} else if fd != 3 {
 				t.Fatalf("Setup: fd = %d, want 3", fd)
 			} else {
-				go func() { encoderDone <- encoder.Encode(payload) }()
+				if err = f.SetDeadline(deadline); err != nil {
+					t.Fatal(err.Error())
+				}
+				go func() { encoderDone <- gob.NewEncoder(f).Encode(payload) }()
 			}
 
 			if len(extraFiles) != 1 {