From 6b7d7d04419ef8ac14a286f491b7d485ff00248d Mon Sep 17 00:00:00 2001
From: Michael Hanselmann <public@hansmi.ch>
Date: Mon, 5 Jul 2021 23:51:12 +0200
Subject: [PATCH] atexit: Terminate with non-zero status after receiving signal

When rclone received a SIGINT (Ctrl+C) or SIGTERM signal while an atexit
function is registered it always terminated with status code 0. Unix
convention is to exit with a non-zero status code. Often it's
`128 + int(signum), but at least not zero.

With this change fatal signals handled by the `atexit` package cause
a non-zero exit code. On Unix systems it's `128 + int(signum)` while
on other systems, such as Windows, it's always 2 ("error not otherwise
categorised").

Resolves #5437.

Signed-off-by: Michael Hanselmann <public@hansmi.ch>
---
 lib/atexit/atexit.go       |  2 +-
 lib/atexit/atexit_other.go |  6 ++++++
 lib/atexit/atexit_test.go  | 41 ++++++++++++++++++++++++++++++++++++++
 lib/atexit/atexit_unix.go  | 14 +++++++++++++
 4 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 lib/atexit/atexit_test.go

diff --git a/lib/atexit/atexit.go b/lib/atexit/atexit.go
index c7b37238a..bcc851847 100644
--- a/lib/atexit/atexit.go
+++ b/lib/atexit/atexit.go
@@ -51,7 +51,7 @@ func Register(fn func()) FnHandle {
 			fs.Infof(nil, "Signal received: %s", sig)
 			Run()
 			fs.Infof(nil, "Exiting...")
-			os.Exit(0)
+			os.Exit(exitCode(sig))
 		}()
 	})
 
diff --git a/lib/atexit/atexit_other.go b/lib/atexit/atexit_other.go
index 15faa7448..bd9f238bf 100644
--- a/lib/atexit/atexit_other.go
+++ b/lib/atexit/atexit_other.go
@@ -4,6 +4,12 @@ package atexit
 
 import (
 	"os"
+
+	"github.com/rclone/rclone/lib/exitcode"
 )
 
 var exitSignals = []os.Signal{os.Interrupt}
+
+func exitCode(_ os.Signal) int {
+	return exitcode.UncategorizedError
+}
diff --git a/lib/atexit/atexit_test.go b/lib/atexit/atexit_test.go
new file mode 100644
index 000000000..6e0315ffe
--- /dev/null
+++ b/lib/atexit/atexit_test.go
@@ -0,0 +1,41 @@
+package atexit
+
+import (
+	"os"
+	"runtime"
+	"testing"
+
+	"github.com/rclone/rclone/lib/exitcode"
+	"github.com/stretchr/testify/assert"
+)
+
+type fakeSignal struct{}
+
+func (*fakeSignal) String() string {
+	return "fake"
+}
+
+func (*fakeSignal) Signal() {
+}
+
+var _ os.Signal = (*fakeSignal)(nil)
+
+func TestExitCode(t *testing.T) {
+	switch runtime.GOOS {
+	case "windows", "plan9":
+		for _, i := range []os.Signal{
+			os.Interrupt,
+			os.Kill,
+		} {
+			assert.Equal(t, exitCode(i), exitcode.UncategorizedError)
+		}
+
+	default:
+		// SIGINT (2) and SIGKILL (9) are portable numbers specified by POSIX.
+		assert.Equal(t, exitCode(os.Interrupt), 128+2)
+		assert.Equal(t, exitCode(os.Kill), 128+9)
+	}
+
+	// Never a real signal
+	assert.Equal(t, exitCode(&fakeSignal{}), exitcode.UncategorizedError)
+}
diff --git a/lib/atexit/atexit_unix.go b/lib/atexit/atexit_unix.go
index acebfaf1c..2df372a1a 100644
--- a/lib/atexit/atexit_unix.go
+++ b/lib/atexit/atexit_unix.go
@@ -5,6 +5,20 @@ package atexit
 import (
 	"os"
 	"syscall"
+
+	"github.com/rclone/rclone/lib/exitcode"
 )
 
 var exitSignals = []os.Signal{syscall.SIGINT, syscall.SIGTERM} // Not syscall.SIGQUIT as we want the default behaviour
+
+// exitCode calculates the exit code for the given signal. Many Unix programs
+// exit with 128+signum if they handle signals. Most shell also implement the
+// same convention if a program is terminated by an uncaught and/or fatal
+// signal.
+func exitCode(sig os.Signal) int {
+	if real, ok := sig.(syscall.Signal); ok && int(real) > 0 {
+		return 128 + int(real)
+	}
+
+	return exitcode.UncategorizedError
+}