Pull request: 3457 fix service reload

Merge in DNS/adguard-home from 3457-darwin-svc-reload to master

Closes #3457.

Squashed commit of the following:

commit e3d6fbccf8373194360b6480e2d702ccd0ec7107
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Aug 18 00:52:39 2021 +0300

    aghos: imp docs

commit 220d37ebc1e0c2e9ba37a34650bff1480bd2fcf6
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Aug 17 15:45:52 2021 +0300

    all: fix ps

internal/aghos/os_test.go

@@ -0,0 +1,98 @@
+package aghos
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghio"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLargestLabeled(t *testing.T) {
+	const (
+		comm = `command-name`
+		nl   = "\n"
+	)
+
+	testCases := []struct {
+		name        string
+		data        []byte
+		wantPID     int
+		wantInstNum int
+	}{{
+		name: "success",
+		data: []byte(nl +
+			`  123     not-a-` + comm + nl +
+			`  321    ` + comm + nl,
+		),
+		wantPID:     321,
+		wantInstNum: 1,
+	}, {
+		name: "several",
+		data: []byte(nl +
+			`1 ` + comm + nl +
+			`5 /` + comm + nl +
+			`2 /some/path/` + comm + nl +
+			`4 ./` + comm + nl +
+			`3 ` + comm + nl +
+			`10 .` + comm + nl,
+		),
+		wantPID:     5,
+		wantInstNum: 5,
+	}, {
+		name: "no_any",
+		data: []byte(nl +
+			`1 ` + `not-a-` + comm + nl +
+			`2 ` + `not-a-` + comm + nl +
+			`3 ` + `not-a-` + comm + nl,
+		),
+		wantPID:     0,
+		wantInstNum: 0,
+	}, {
+		name: "weird_input",
+		data: []byte(nl +
+			`abc  ` + comm + nl +
+			`-1   ` + comm + nl,
+		),
+		wantPID:     0,
+		wantInstNum: 0,
+	}}
+
+	for _, tc := range testCases {
+		r := bytes.NewReader(tc.data)
+
+		t.Run(tc.name, func(t *testing.T) {
+			pid, instNum, err := parsePSOutput(r, comm)
+			require.NoError(t, err)
+
+			assert.Equal(t, tc.wantPID, pid)
+			assert.Equal(t, tc.wantInstNum, instNum)
+		})
+	}
+
+	t.Run("scanner_fail", func(t *testing.T) {
+		lr, err := aghio.LimitReader(bytes.NewReader([]byte{1, 2, 3}), 0)
+		require.NoError(t, err)
+
+		target := &aghio.LimitReachedError{}
+		_, _, err = parsePSOutput(lr, "")
+		require.ErrorAs(t, err, &target)
+
+		assert.EqualValues(t, 0, target.Limit)
+	})
+
+	t.Run("ignore", func(t *testing.T) {
+		r := bytes.NewReader([]byte(nl +
+			`1 ` + comm + nl +
+			`2 ` + comm + nl +
+			`3` + comm + nl,
+		))
+
+		pid, instances, err := parsePSOutput(r, comm, 1, 3)
+		require.NoError(t, err)
+
+		assert.Equal(t, 2, pid)
+		assert.Equal(t, 1, instances)
+	})
+}