IP_STATUS_FILE and routing improvements (#130)

- Obtains VPN public IP address from routing table
- Logs and writes VPN Public IP address to `/ip` as soon as VPN is up
- Obtain port forward, logs it and writes it as soon as VPN is up
- Routing fully refactored and tested
- Routing reads from `/proc/net/route`
- Routing mutates the routes using `ip route ...`

internal/routing/mutate_test.go

@@ -0,0 +1,67 @@
+package routing
+
+import (
+	"fmt"
+	"net"
+	"testing"
+
+	gomock "github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+//go:generate mockgen -destination=mockCommander_test.go -package=routing github.com/qdm12/golibs/command Commander
+
+func Test_removeRoute(t *testing.T) {
+	t.Parallel()
+	tests := map[string]struct {
+		subnet    net.IPNet
+		runOutput string
+		runErr    error
+		err       error
+	}{
+		"no output no error": {
+			subnet: net.IPNet{
+				IP:   net.IP{192, 168, 1, 0},
+				Mask: net.IPMask{255, 255, 255, 0},
+			},
+		},
+		"error only": {
+			subnet: net.IPNet{
+				IP:   net.IP{192, 168, 1, 0},
+				Mask: net.IPMask{255, 255, 255, 0},
+			},
+			runErr: fmt.Errorf("error"),
+			err:    fmt.Errorf("cannot delete route for 192.168.1.0/24: : error"),
+		},
+		"error and output": {
+			subnet: net.IPNet{
+				IP:   net.IP{192, 168, 1, 0},
+				Mask: net.IPMask{255, 255, 255, 0},
+			},
+			runErr:    fmt.Errorf("error"),
+			runOutput: "output",
+			err:       fmt.Errorf("cannot delete route for 192.168.1.0/24: output: error"),
+		},
+	}
+	for name, tc := range tests {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			mockCtrl := gomock.NewController(t)
+			defer mockCtrl.Finish()
+			mockCommander := NewMockCommander(mockCtrl)
+
+			mockCommander.EXPECT().Run("ip", "route", "del", tc.subnet.String()).
+				Return(tc.runOutput, tc.runErr).Times(1)
+			r := &routing{commander: mockCommander}
+			err := r.removeRoute(tc.subnet)
+			if tc.err != nil {
+				require.Error(t, err)
+				assert.Equal(t, tc.err.Error(), err.Error())
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}