all: move wgcfg from wireguard-go

This is mostly code movement from the wireguard-go repo.

Most of the new wgcfg package corresponds to the wireguard-go wgcfg package.

wgengine/wgcfg/device{_test}.go was device/config{_test}.go.
There were substantive but simple changes to device_test.go to remove
internal package device references.

The API of device.Config (now wgcfg.DeviceConfig) grew an error return;
we previously logged the error and threw it away.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

wgengine/wgcfg/key_test.go

@@ -0,0 +1,111 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package wgcfg
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestKeyBasics(t *testing.T) {
+	k1, err := NewPresharedKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b, err := k1.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("JSON round-trip", func(t *testing.T) {
+		// should preserve the keys
+		k2 := new(Key)
+		if err := k2.UnmarshalJSON(b); err != nil {
+			t.Fatal(err)
+		}
+		if !bytes.Equal(k1[:], k2[:]) {
+			t.Fatalf("k1 %v != k2 %v", k1[:], k2[:])
+		}
+		if b1, b2 := k1.String(), k2.String(); b1 != b2 {
+			t.Fatalf("base64-encoded keys do not match: %s, %s", b1, b2)
+		}
+	})
+
+	t.Run("JSON incompatible with PrivateKey", func(t *testing.T) {
+		k2 := new(PrivateKey)
+		if err := k2.UnmarshalText(b); err == nil {
+			t.Fatalf("successfully decoded key as private key")
+		}
+	})
+
+	t.Run("second key", func(t *testing.T) {
+		// A second call to NewPresharedKey should make a new key.
+		k3, err := NewPresharedKey()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if bytes.Equal(k1[:], k3[:]) {
+			t.Fatalf("k1 %v == k3 %v", k1[:], k3[:])
+		}
+		// Check for obvious comparables to make sure we are not generating bad strings somewhere.
+		if b1, b2 := k1.String(), k3.String(); b1 == b2 {
+			t.Fatalf("base64-encoded keys match: %s, %s", b1, b2)
+		}
+	})
+}
+func TestPrivateKeyBasics(t *testing.T) {
+	pri, err := NewPrivateKey()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b, err := pri.MarshalText()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("JSON round-trip", func(t *testing.T) {
+		// should preserve the keys
+		pri2 := new(PrivateKey)
+		if err := pri2.UnmarshalText(b); err != nil {
+			t.Fatal(err)
+		}
+		if !bytes.Equal(pri[:], pri2[:]) {
+			t.Fatalf("pri %v != pri2 %v", pri[:], pri2[:])
+		}
+		if b1, b2 := pri.String(), pri2.String(); b1 != b2 {
+			t.Fatalf("base64-encoded keys do not match: %s, %s", b1, b2)
+		}
+		if pub1, pub2 := pri.Public().String(), pri2.Public().String(); pub1 != pub2 {
+			t.Fatalf("base64-encoded public keys do not match: %s, %s", pub1, pub2)
+		}
+	})
+
+	t.Run("JSON incompatible with Key", func(t *testing.T) {
+		k2 := new(Key)
+		if err := k2.UnmarshalJSON(b); err == nil {
+			t.Fatalf("successfully decoded private key as key")
+		}
+	})
+
+	t.Run("second key", func(t *testing.T) {
+		// A second call to New should make a new key.
+		pri3, err := NewPrivateKey()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if bytes.Equal(pri[:], pri3[:]) {
+			t.Fatalf("pri %v == pri3 %v", pri[:], pri3[:])
+		}
+		// Check for obvious comparables to make sure we are not generating bad strings somewhere.
+		if b1, b2 := pri.String(), pri3.String(); b1 == b2 {
+			t.Fatalf("base64-encoded keys match: %s, %s", b1, b2)
+		}
+		if pub1, pub2 := pri.Public().String(), pri3.Public().String(); pub1 == pub2 {
+			t.Fatalf("base64-encoded public keys match: %s, %s", pub1, pub2)
+		}
+	})
+}