Persist virtual session processes for crash recovery and identify them by start time

client/vnc/server/shutdown_state_test.go

@@ -0,0 +1,79 @@
+//go:build unix
+
+package server
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// The start time is what tells a recorded process apart from whatever later
+// inherits its PID, so the field offset has to be right and the value stable.
+func TestProcessStartTimeIsStable(t *testing.T) {
+	if _, err := os.Stat("/proc/self/stat"); err != nil {
+		t.Skip("no procfs")
+	}
+
+	pid := os.Getpid()
+	first, err := processStartTime(pid)
+	require.NoError(t, err)
+	assert.NotZero(t, first, "a running process has a non-zero start time")
+
+	second, err := processStartTime(pid)
+	require.NoError(t, err)
+	assert.Equal(t, first, second, "start time must not move for a live process")
+}
+
+// A comm containing spaces and parentheses must not shift the field offsets,
+// which is why parsing starts from the last ')' rather than splitting the line.
+func TestProcessStartTimeToleratesOddCommName(t *testing.T) {
+	if _, err := os.Stat("/proc/self/stat"); err != nil {
+		t.Skip("no procfs")
+	}
+	sh, err := exec.LookPath("sh")
+	if err != nil {
+		t.Skip("no shell")
+	}
+
+	// argv[0] becomes the comm, truncated to 15 chars by the kernel.
+	cmd := exec.Command(sh, "-c", "sleep 30")
+	cmd.Args[0] = "a (b) c"
+	require.NoError(t, cmd.Start())
+	t.Cleanup(func() {
+		_ = cmd.Process.Kill()
+		_, _ = cmd.Process.Wait()
+	})
+
+	got, err := processStartTime(cmd.Process.Pid)
+	require.NoError(t, err)
+	assert.NotZero(t, got)
+}
+
+// A PID that never existed must not be reported as ours, and neither must a
+// record that carries no start time to compare against.
+func TestIsOurProcessRefusesUnidentifiableRecords(t *testing.T) {
+	assert.False(t, isOurProcess(sessionProcess{PID: -1}, "xvfb:50"))
+
+	pid := os.Getpid()
+	assert.False(t, isOurProcess(sessionProcess{PID: pid}, "xvfb:50"),
+		"a record with no recorded start time cannot be matched and must be refused")
+}
+
+// describeProcess captures enough to match the process back to itself.
+func TestDescribeProcessRoundTrips(t *testing.T) {
+	if _, err := os.Stat("/proc/self/stat"); err != nil {
+		t.Skip("no procfs")
+	}
+
+	proc := describeProcess(os.Getpid())
+	assert.Equal(t, os.Getpid(), proc.PID)
+	assert.NotZero(t, proc.StartTime)
+
+	start, err := processStartTime(proc.PID)
+	require.NoError(t, err)
+	assert.Equal(t, start, proc.StartTime)
+}