[3.5]backport: pkg/expect: avoid hardcoding when checking ErrProcessDone

ExpectProcess's Stop method uses 'strings.Contains' to check
the returned err, however, this can be avoided. os.ErrProcessDone's
error message is the same as the hardcoded string. So I think
this explicit error is what this method wants to compare.

Signed-off-by: Jes Cok <[email protected]>

Author: callthingsoff

pkg/expect/expect.go

@@ -18,6 +18,7 @@ package expect
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -141,8 +142,56 @@ func (ep *ExpectProcess) LineCount() int {
 	return ep.count
 }
 
-// Stop kills the expect process and waits for it to exit.
-func (ep *ExpectProcess) Stop() error { return ep.close(true) }
+// ExitCode returns the exit code of this process.
+// If the process is still running, it returns exit code 0 and ErrProcessRunning.
+func (ep *ExpectProcess) ExitCode() (int, error) {
+	ep.mu.Lock()
+	defer ep.mu.Unlock()
+
+	if ep.cmd == nil {
+		return ep.exitCode, nil
+	}
+
+	if ep.exitErr != nil {
+		// If the child process panics or is killed, for instance, the
+		// goFailpoint triggers the exit event, the ep.cmd isn't nil and
+		// the exitCode will describe the case.
+		if ep.exitCode != 0 {
+			return ep.exitCode, nil
+		}
+
+		// If the wait4(2) in waitProcess returns error, the child
+		// process might be reaped if the process handles the SIGCHILD
+		// in other goroutine. It's unlikely in this repo. But we
+		// should return the error for log even if the child process
+		// is still running.
+		return 0, ep.exitErr
+	}
+
+	return 0, ErrProcessRunning
+}
+
+// ExitError returns the exit error of this process (if any).
+// If the process is still running, it returns ErrProcessRunning instead.
+func (ep *ExpectProcess) ExitError() error {
+	ep.mu.Lock()
+	defer ep.mu.Unlock()
+
+	if ep.cmd == nil {
+		return ep.exitErr
+	}
+
+	return ErrProcessRunning
+}
+
+// Stop signals the process to terminate via SIGTERM
+func (ep *ExpectProcess) Stop() error {
+	err := ep.Signal(syscall.SIGTERM)
+	if err != nil && errors.Is(err, os.ErrProcessDone) {
+		return nil
+	}
+	return err
+}
 
 // Signal sends a signal to the expect process
 func (ep *ExpectProcess) Signal(sig os.Signal) error {