Rewrite of the entrypoint in Golang (#71)

- General improvements
    - Parallel download of only needed files at start
    - Prettier console output with all streams merged (openvpn, unbound, shadowsocks etc.)
    - Simplified Docker final image
    - Faster bootup
- DNS over TLS
    - Finer grain blocking at DNS level: malicious, ads and surveillance
    - Choose your DNS over TLS providers
    - Ability to use multiple DNS over TLS providers for DNS split horizon
    - Environment variables for DNS logging
    - DNS block lists needed are downloaded and built automatically at start, in parallel
- PIA
    - A random region is selected if the REGION parameter is left empty (thanks @rorph for your PR)
    - Routing and iptables adjusted so it can work as a Kubernetes pod sidecar (thanks @rorph for your PR)

internal/dns/os_test.go

@@ -0,0 +1,72 @@
+package dns
+
+import (
+	"fmt"
+	"testing"
+
+	filesmocks "github.com/qdm12/golibs/files/mocks"
+	loggingmocks "github.com/qdm12/golibs/logging/mocks"
+	"github.com/qdm12/private-internet-access-docker/internal/constants"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_SetLocalNameserver(t *testing.T) {
+	t.Parallel()
+	tests := map[string]struct {
+		data        []byte
+		writtenData []byte
+		readErr     error
+		writeErr    error
+		err         error
+	}{
+		"no data": {
+			writtenData: []byte("nameserver 127.0.0.1"),
+		},
+		"read error": {
+			readErr: fmt.Errorf("error"),
+			err:     fmt.Errorf("error"),
+		},
+		"write error": {
+			writtenData: []byte("nameserver 127.0.0.1"),
+			writeErr:    fmt.Errorf("error"),
+			err:         fmt.Errorf("error"),
+		},
+		"lines without nameserver": {
+			data:        []byte("abc\ndef\n"),
+			writtenData: []byte("abc\ndef\nnameserver 127.0.0.1"),
+		},
+		"lines with nameserver": {
+			data:        []byte("abc\nnameserver abc def\ndef\n"),
+			writtenData: []byte("abc\nnameserver 127.0.0.1\ndef"),
+		},
+	}
+	for name, tc := range tests {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			fileManager := &filesmocks.FileManager{}
+			fileManager.On("ReadFile", string(constants.ResolvConf)).
+				Return(tc.data, tc.readErr).Once()
+			if tc.readErr == nil {
+				fileManager.On("WriteToFile", string(constants.ResolvConf), tc.writtenData).
+					Return(tc.writeErr).Once()
+			}
+			logger := &loggingmocks.Logger{}
+			logger.On("Info", "%s: setting local nameserver to 127.0.0.1", logPrefix).Once()
+			c := &configurator{
+				fileManager: fileManager,
+				logger:      logger,
+			}
+			err := c.SetLocalNameserver()
+			if tc.err != nil {
+				require.Error(t, err)
+				assert.Equal(t, tc.err.Error(), err.Error())
+			} else {
+				assert.NoError(t, err)
+			}
+			fileManager.AssertExpectations(t)
+			logger.AssertExpectations(t)
+		})
+	}
+}