Persist authorization key

Useful until step 2 stops failing half the time

.gitignore

@@ -7,3 +7,6 @@ build/
 **/tl/Abstract.java
 **/tl/Types.java
 **/tl/Functions.java
+
+# Authorization Key
+*.key

lib/src/main/java/io/github/lonamiwebs/overgram/Overgram.java

@@ -1,19 +1,42 @@
 package io.github.lonamiwebs.overgram;
 
+import io.github.lonamiwebs.overgram.crypto.AuthKey;
 import io.github.lonamiwebs.overgram.network.MTProtoSender;
 import io.github.lonamiwebs.overgram.network.MTProtoState;
 import io.github.lonamiwebs.overgram.network.connection.TcpFull;
 import io.github.lonamiwebs.overgram.tl.Functions;
 
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
 import java.io.IOException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 
 public class Overgram {
+    private static void saveAuthKey(final AuthKey authKey, final File file) {
+        try (final FileOutputStream out = new FileOutputStream(file)) {
+            out.write(authKey.key);
+        } catch (IOException ignored) {
+        }
+    }
+
+    private static AuthKey loadAuthKey(final File file) {
+        try (final FileInputStream in = new FileInputStream(file)) {
+            final byte[] key = new byte[256];
+            assert in.read(key) == key.length;
+            return new AuthKey(key);
+        } catch (IOException ignored) {
+            return null;
+        }
+    }
+
     public static void main(final String... args) throws IOException, InterruptedException, ExecutionException {
-        final MTProtoSender sender = new MTProtoSender(new MTProtoState(), new TcpFull());
+        final File authKey = new File("auth.key");
+        final MTProtoSender sender = new MTProtoSender(new MTProtoState(loadAuthKey(authKey)), new TcpFull());
         try {
             sender.connect("149.154.167.91", 443);
+            saveAuthKey(sender.state.authKey, authKey);
             final Future result = sender.send(new Functions.Ping());
             System.out.println(result.get());
         } finally {

lib/src/main/java/io/github/lonamiwebs/overgram/network/MTProtoPlainSender.java

@@ -15,7 +15,7 @@ public class MTProtoPlainSender {
 
     public MTProtoPlainSender(final Connection connection) {
         this.connection = connection;
-        this.state = new MTProtoState();
+        this.state = new MTProtoState(null);
     }
 
     public <T extends TLObject> T send(final TLRequest request) throws IOException, ClassNotFoundException {

lib/src/main/java/io/github/lonamiwebs/overgram/network/MTProtoSender.java

@@ -16,7 +16,7 @@ import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 
 public class MTProtoSender {
-    private final MTProtoState state;
+    public final MTProtoState state;
     private final Connection connection;
     private String ip;
     private int port;

lib/src/main/java/io/github/lonamiwebs/overgram/network/MTProtoState.java

@@ -23,13 +23,13 @@ public class MTProtoState {
     private int sequence;
     private long lastMsgId;
 
-    public MTProtoState() {
+    public MTProtoState(final AuthKey authKey) {
+        this.authKey = authKey;
+        salt = 0;
         id = new SecureRandom().nextLong();
         timeOffset = 0;
         sequence = 0;
         lastMsgId = 0;
-        authKey = null;
-        salt = 0;
     }
 
     public TLMessage createMessage(final TLObject object) {