Add new obfuscation package

mtglib/internal/obfuscation/conn.go

@@ -0,0 +1,34 @@
+package obfuscation
+
+import (
+	"crypto/cipher"
+
+	"github.com/9seconds/mtg/v2/essentials"
+)
+
+type conn struct {
+	essentials.Conn
+
+	sendCipher cipher.Stream
+	recvCipher cipher.Stream
+}
+
+func (c conn) Read(p []byte) (int, error) {
+	n, err := c.Conn.Read(p)
+	if err != nil {
+		return n, err
+	}
+
+	c.recvCipher.XORKeyStream(p, p[:n])
+
+	return n, nil
+}
+
+func (c conn) Write(p []byte) (int, error) {
+	// yes, this is a bit violent and goes against a contract in io.Writer
+	// but we do it to avoid creating a new buffer just to perform this
+	// encryption.
+	c.sendCipher.XORKeyStream(p, p)
+
+	return c.Conn.Write(p)
+}