chore(all): memory and thread safe storage

- settings: get filter choices from storage for settings validation
- updater: update servers to the storage
- storage: minimal deep copying and data duplication
- storage: add merged servers mutex for thread safety
- connection: filter servers in storage
- formatter: format servers to Markdown in storage
- PIA: get server by name from storage directly
- Updater: get servers count from storage directly
- Updater: equality check done in storage, fix #882

internal/storage/copy_test.go

@@ -0,0 +1,75 @@
+package storage
+
+import (
+	"net"
+	"testing"
+
+	"github.com/qdm12/gluetun/internal/models"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_copyServer(t *testing.T) {
+	t.Parallel()
+
+	server := models.Server{
+		Country: "a",
+		IPs:     []net.IP{{1, 2, 3, 4}},
+	}
+
+	serverCopy := copyServer(server)
+
+	assert.Equal(t, server, serverCopy)
+	// Check for mutation
+	serverCopy.IPs[0][0] = 9
+	assert.NotEqual(t, server, serverCopy)
+}
+
+func Test_copyIPs(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		toCopy []net.IP
+		copied []net.IP
+	}{
+		"nil": {},
+		"empty": {
+			toCopy: []net.IP{},
+			copied: []net.IP{},
+		},
+		"single IP": {
+			toCopy: []net.IP{{1, 1, 1, 1}},
+			copied: []net.IP{{1, 1, 1, 1}},
+		},
+		"two IPs": {
+			toCopy: []net.IP{{1, 1, 1, 1}, {2, 2, 2, 2}},
+			copied: []net.IP{{1, 1, 1, 1}, {2, 2, 2, 2}},
+		},
+	}
+
+	for name, testCase := range testCases {
+		testCase := testCase
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			// Reserver leading 9 for copy modifications below
+			for _, ipToCopy := range testCase.toCopy {
+				require.NotEqual(t, 9, ipToCopy[0])
+			}
+
+			copied := copyIPs(testCase.toCopy)
+
+			assert.Equal(t, testCase.copied, copied)
+
+			if len(copied) > 0 {
+				original := testCase.toCopy[0][0]
+				testCase.toCopy[0][0] = 9
+				assert.NotEqual(t, 9, copied[0][0])
+				testCase.toCopy[0][0] = original
+
+				copied[0][0] = 9
+				assert.NotEqual(t, 9, testCase.toCopy[0][0])
+			}
+		})
+	}
+}