internal/store: destroy stale instances

This recovers from inconsistent state on power loss and /tmp/ is not wiped on startup, or if hakurei somehow crashes.

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

1 files changed, 37 insertions, 2 deletions

diff --git a/internal/store/segment.go b/internal/store/segment.go
index 32c8a141..8b7dd0d6 100644
--- a/internal/store/segment.go
+++ b/internal/store/segment.go
@@ -7,6 +7,7 @@ import (
 	"os"
 	"strconv"
 	"sync"
+	"syscall"
 
 	"hakurei.app/check"
 	"hakurei.app/hst"
@@ -76,13 +77,20 @@ func (eh *EntryHandle) save(state *hst.State) error {
 	return err
 }
 
+// KillFunc is the function signature of syscall.Kill.
+type KillFunc func(pid int, sig syscall.Signal) (err error)
+
 // Load loads and validates the state entry header, and returns the
 // [hst.Enablements] byte. For a non-nil v, the full state payload is decoded
-// and stored in the value pointed to by v.
+// and stored in the value pointed to by v, and if kill is non-nil, the presence
+// of the monitoring process is checked, and a stale entry is destroyed.
 //
 // Load validates the embedded [hst.Config] value. A non-nil error returned by
 // Load is of type [hst.AppError].
-func (eh *EntryHandle) Load(v *hst.State) (hst.Enablements, error) {
+func (eh *EntryHandle) Load(
+	v *hst.State,
+	kill KillFunc,
+) (hst.Enablements, error) {
 	f, err := eh.open(os.O_RDONLY, 0)
 	if err != nil {
 		return 0, err
@@ -101,6 +109,33 @@ func (eh *EntryHandle) Load(v *hst.State) (hst.Enablements, error) {
 				),
 			}
 		}
+		if kill != nil {
+			errno := kill(v.PID, 0)
+			if errno != nil {
+				if !errors.Is(errno, syscall.ESRCH) {
+					err = &hst.AppError{
+						Step: "check monitor process",
+						Err:  errno,
+					}
+				} else {
+					if err = eh.Destroy(); err != nil {
+						err = &hst.AppError{
+							Step: "destroy stale entry",
+							Err:  err,
+						}
+					} else {
+						err = &hst.AppError{
+							Step: "load stale entry",
+							Err:  errno,
+							Msg: fmt.Sprintf(
+								"stale entry %s",
+								eh.ID.String(),
+							),
+						}
+					}
+				}
+			}
+		}
 	} else {
 		et, err = entryDecodeHeader(f)
 	}