s6: add signaling package

1 files changed, 37 insertions, 0 deletions

diff --git a/s6/signal.go b/s6/signal.go
new file mode 100644
index 0000000..f754bbe
--- /dev/null
+++ b/s6/signal.go
@@ -0,0 +1,37 @@
+// Package s6 allows Go programs to signal readiness to the s6[1] suite of system
+// supervision tools. This should be run in func main.
+//
+// [1]: http://skarnet.org/software/s6/index.html
+package s6
+
+import (
+	"errors"
+	"flag"
+	"os"
+)
+
+var (
+	ErrCantFindNotificationFD = errors.New("s6: can't find notification file descriptor")
+	notificationFD            = flag.Int("notification-fd", 0, "notification file descriptor")
+)
+
+// Signal signals readiness to s6.
+//
+// See: http://skarnet.org/software/s6/notifywhenup.html
+func Signal() error {
+	var err error
+
+	// If this is unset, we probably don't care about notifying s6.
+	if *notificationFD == 0 {
+		return nil
+	}
+
+	fout := os.NewFile(uintptr(*notificationFD), "s6-notification")
+	if fout == nil {
+		return ErrCantFindNotificationFD
+	}
+	defer fout.Close()
+
+	_, err = fout.Write([]byte("\n"))
+	return err
+}