container/init: measure init behaviour

This used to be entirely done via integration tests, with almost no hope of error injection and coverage profile. These tests significantly increase confidence of future work in this area.

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

container/dispatcher_test.go

@@ -3,7 +3,6 @@ package container
 import (
 	"bytes"
 	"errors"
-	"fmt"
 	"io"
 	"io/fs"
 	"os"
@@ -114,6 +113,7 @@ type simpleTestCase struct {
 func checkSimple(t *testing.T, fname string, testCases []simpleTestCase) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
+			defer handleExitStub(t, "check")
 			k := &kstub{t: t, want: tc.want, wg: new(sync.WaitGroup)}
 			if err := tc.f(k); !errors.Is(err, tc.wantErr) {
 				t.Errorf("%s: error = %v, want %v", fname, err, tc.wantErr)
@@ -170,6 +170,8 @@ func checkOpBehaviour(t *testing.T, testCases []opBehaviourTestCase) {
 	})
 }
 
+func sliceAddr[S any](s []S) *[]S { return &s }
+
 func newCheckedFile(t *testing.T, name, wantData string, closeErr error) osFile {
 	f := &checkedOsFile{t: t, name: name, want: wantData, closeErr: closeErr}
 	// check happens in Close, and cleanup is not guaranteed to run, so relying on it for sloppy implementations will cause sporadic test results
@@ -263,6 +265,17 @@ func (k *kexpect) error(ok ...bool) error {
 	return syscall.ENOTRECOVERABLE
 }
 
+func handleExitStub(t *testing.T, prefix string) {
+	r := recover()
+	if r == 0xdeadbeef {
+		t.Log(prefix + " terminated on an exit stub")
+		return
+	}
+	if r != nil {
+		panic(r)
+	}
+}
+
 type kstub struct {
 	t *testing.T
 
@@ -344,7 +357,11 @@ func (k *kstub) new(f func(k syscallDispatcher)) {
 	sk := &kstub{t: k.t, want: k.want, track: len(k.sub) + 1, wg: k.wg}
 	k.sub = append(k.sub, sk)
 	k.wg.Add(1)
-	go func() { defer k.wg.Done(); f(sk) }()
+	go func() {
+		defer k.wg.Done()
+		defer handleExitStub(k.t, "goroutine")
+		f(sk)
+	}()
 }
 
 func (k *kstub) lockOSThread() { k.expect("lockOSThread") }
@@ -390,10 +407,45 @@ func (k *kstub) isatty(fd int) bool {
 
 func (k *kstub) receive(key string, e any, fdp *uintptr) (closeFunc func() error, err error) {
 	expect := k.expect("receive")
-	return expect.ret.(func() error), expect.error(
+
+	var closed bool
+	closeFunc = func() error {
+		if closed {
+			k.t.Error("closeFunc called more than once")
+			return os.ErrClosed
+		}
+		closed = true
+
+		if expect.ret != nil {
+			// use return stored in kexpect for closeFunc instead
+			return expect.ret.(error)
+		}
+		return nil
+	}
+	err = expect.error(
 		checkArg(k, "key", key, 0),
 		checkArgReflect(k, "e", e, 1),
-		checkArg(k, "fdp", fdp, 2))
+		checkArgReflect(k, "fdp", fdp, 2))
+
+	// 3 is unused so stores params
+	if expect.args[3] != nil {
+		if v, ok := expect.args[3].(*initParams); ok && v != nil {
+			if p, ok0 := e.(*initParams); ok0 && p != nil {
+				*p = *v
+			}
+		}
+	}
+
+	// 4 is unused so stores fd
+	if expect.args[4] != nil {
+		if v, ok := expect.args[4].(uintptr); ok && v >= 3 {
+			if fdp != nil {
+				*fdp = v
+			}
+		}
+	}
+
+	return
 }
 
 func (k *kstub) bindMount(source, target string, flags uintptr, eq bool) error {
@@ -441,20 +493,23 @@ func (k *kstub) notify(c chan<- os.Signal, sig ...os.Signal) {
 	}
 
 	// export channel for external instrumentation
-	if chanp, ok := expect.args[0].(*chan<- os.Signal); ok && chanp != nil {
-		if *chanp != nil {
-			panic(fmt.Sprintf("attempting reuse of %p", chanp))
-		}
-		*chanp = c
+	if chanf, ok := expect.args[0].(func(c chan<- os.Signal)); ok && chanf != nil {
+		chanf(c)
 	}
 }
 
 func (k *kstub) start(c *exec.Cmd) error {
-	return k.expect("start").error(
+	expect := k.expect("start")
+	err := expect.error(
 		checkArg(k, "c.Path", c.Path, 0),
 		checkArgReflect(k, "c.Args", c.Args, 1),
 		checkArgReflect(k, "c.Env", c.Env, 2),
 		checkArg(k, "c.Dir", c.Dir, 3))
+
+	if process, ok := expect.ret.(*os.Process); ok && process != nil {
+		c.Process = process
+	}
+	return err
 }
 
 func (k *kstub) signal(c *exec.Cmd, sig os.Signal) error {
@@ -477,6 +532,7 @@ func (k *kstub) exit(code int) {
 	if !checkArg(k, "code", code, 0) {
 		k.t.FailNow()
 	}
+	panic(0xdeadbeef)
 }
 
 func (k *kstub) getpid() int { return k.expect("getpid").ret.(int) }
@@ -618,11 +674,25 @@ func (k *kstub) unmount(target string, flags int) (err error) {
 
 func (k *kstub) wait4(pid int, wstatus *syscall.WaitStatus, options int, rusage *syscall.Rusage) (wpid int, err error) {
 	expect := k.expect("wait4")
-	return expect.ret.(int), expect.error(
+	// special case to prevent leaking the wait4 goroutine when testing initEntrypoint
+	if v, ok := expect.args[4].(int); ok && v == 0xdeadbeef {
+		k.t.Log("terminating current goroutine as requested by kexpect")
+		panic(0xdeadbeef)
+	}
+
+	wpid = expect.ret.(int)
+	err = expect.error(
 		checkArg(k, "pid", pid, 0),
-		checkArg(k, "wstatus", wstatus, 1),
-		checkArg(k, "options", options, 2),
-		checkArg(k, "rusage", rusage, 3))
+		checkArg(k, "options", options, 2))
+
+	if wstatusV, ok := expect.args[1].(syscall.WaitStatus); wstatus != nil && ok {
+		*wstatus = wstatusV
+	}
+	if rusageV, ok := expect.args[3].(syscall.Rusage); rusage != nil && ok {
+		*rusage = rusageV
+	}
+
+	return
 }
 
 func (k *kstub) printf(format string, v ...any) {
@@ -638,6 +708,7 @@ func (k *kstub) fatal(v ...any) {
 		checkArgReflect(k, "v", v, 0)) != nil {
 		k.t.FailNow()
 	}
+	panic(0xdeadbeef)
 }
 
 func (k *kstub) fatalf(format string, v ...any) {
@@ -646,6 +717,7 @@ func (k *kstub) fatalf(format string, v ...any) {
 		checkArgReflect(k, "v", v, 1)) != nil {
 		k.t.FailNow()
 	}
+	panic(0xdeadbeef)
 }
 
 func (k *kstub) verbose(v ...any) {