Add fuzz tests for obfuscated2

mtglib/internal/obfuscated2/init_test.go

@@ -1,12 +1,20 @@
 package obfuscated2_test
 
 import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
+	"testing"
+
+	"github.com/9seconds/mtg/v2/internal/testlib"
+	"github.com/9seconds/mtg/v2/mtglib/internal/obfuscated2"
+	"github.com/stretchr/testify/require"
 )
 
 type snapshotBytes struct {
@@ -50,6 +58,14 @@ type SnapshotTestSuite struct {
 	snapshots map[string]*Obfuscated2Snapshot
 }
 
+type ServerHandshakeTestData struct {
+	connMock *testlib.EssentialsConnMock
+
+	proxyConn obfuscated2.Conn
+	encryptor cipher.Stream
+	decryptor cipher.Stream
+}
+
 func (suite *SnapshotTestSuite) IngestSnapshots(dirname, namePrefix string) error {
 	suite.snapshots = map[string]*Obfuscated2Snapshot{}
 
@@ -81,3 +97,41 @@ func (suite *SnapshotTestSuite) IngestSnapshots(dirname, namePrefix string) erro
 
 	return nil
 }
+
+func NewServerHandshakeTestData(t *testing.T) ServerHandshakeTestData {
+	buf := &bytes.Buffer{}
+	connMock := &testlib.EssentialsConnMock{}
+
+	handshakeEnc, handshakeDec, err := obfuscated2.ServerHandshake(buf)
+	require.NoError(t, err)
+
+	serverEncrypted := buf.Bytes()
+	decBlock, _ := aes.NewCipher(serverEncrypted[8 : 8+32])
+	decryptor := cipher.NewCTR(decBlock, serverEncrypted[8+32:8+32+16])
+
+	serverDecrypted := make([]byte, len(serverEncrypted))
+	decryptor.XORKeyStream(serverDecrypted, serverEncrypted)
+
+	require.Equal(t, "3d3d3Q",
+		base64.RawStdEncoding.EncodeToString(serverDecrypted[8+32+16:8+32+16+4]))
+
+	serverEncryptedReverted := make([]byte, len(serverEncrypted))
+
+	for i := 0; i < 32+16; i++ {
+		serverEncryptedReverted[8+i] = serverEncrypted[8+32+16-1-i]
+	}
+
+	encBlock, _ := aes.NewCipher(serverEncryptedReverted[8 : 8+32])
+	encryptor := cipher.NewCTR(encBlock, serverEncryptedReverted[8+32:8+32+16])
+
+	return ServerHandshakeTestData{
+		connMock: connMock,
+		proxyConn: obfuscated2.Conn{
+			Conn: connMock,
+			Encryptor: handshakeEnc,
+			Decryptor: handshakeDec,
+		},
+		encryptor: encryptor,
+		decryptor: decryptor,
+	}
+}