diff --git a/client/src/connection.vala b/client/src/connection.vala
index 98eb61a..6311344 100644
--- a/client/src/connection.vala
+++ b/client/src/connection.vala
@@ -50,172 +50,5 @@ namespace StudySystemClient {
 				Thread.usleep(1000 * TASK_PERIOD_MS);
 			}
 		}
-
-	}
-
-	private class SessionManager {
-		public delegate void ReceiveCallback(uint8[] msg);
-
-		private const uint INIT_RECONNECT_WAIT_MS = 500;
-		private const uint MAX_RECONNECT_WAIT_MS = 60000;
-		private const double RECONNECT_BACKOFF = 1.6;
-
-		private SessionFactory session_factory;
-		private ReceiveCallback receive_callback;
-		private Session? session;
-		private AsyncQueue<OutgoingMessage> queue;
-		private uint reconnect_wait_ms;
-
-		public SessionManager(SessionFactory session_factory,
-							  owned ReceiveCallback receive_callback) {
-			this.session_factory = session_factory;
-			this.receive_callback = (owned) receive_callback;
-			this.session = null;
-			queue = new AsyncQueue<OutgoingMessage>();
-			reconnect_wait_ms = INIT_RECONNECT_WAIT_MS;
-		}
-
-		public void send(uint8[] msg) {
-			queue.push(new OutgoingMessage(msg));
-		}
-
-		public void task() {
-			if (session != null) {
-				var failed_msg = session.task(queue);
-				if (failed_msg != null)
-					handle_failed_msg(failed_msg);
-			} else {
-				try_start_session();
-			}
-		}
-
-		private void handle_failed_msg(OutgoingMessage msg) {
-			msg.has_failed();
-			if (msg.should_retry())
-				queue.push(msg);
-			session = null;
-		}
-
-		private void try_start_session() {
-			try {
-				session = session_factory.start_session();
-				session.received.connect(
-					(msg) => receive_callback(msg));
-				reconnect_wait_ms = INIT_RECONNECT_WAIT_MS;
-			} catch (Error _) {
-				Thread.usleep(1000 * reconnect_wait_ms);
-				update_reconnect_wait();
-			}
-		}
-
-		private void update_reconnect_wait() {
-			var new_wait = RECONNECT_BACKOFF * reconnect_wait_ms;
-			if (new_wait < MAX_RECONNECT_WAIT_MS)
-				reconnect_wait_ms = (uint)new_wait;
-			else
-				reconnect_wait_ms = MAX_RECONNECT_WAIT_MS;
-		}
-	}
-
-	private class SessionFactory {
-		private const string CA_FILENAME = "/ca.pem";
-		private const string CERT_FILENAME = "/client.pem";
-		private const uint TIMEOUT_S = 1;
-
-		private InetSocketAddress host;
-		private TlsCertificate cert;
-		private TlsDatabase ca_db;
-
-		public SessionFactory(InetAddress host_addr, uint16 host_port,
-							  string cert_dir) throws Error {
-			host = new InetSocketAddress(host_addr, host_port);
-			var cert_path = cert_dir + CERT_FILENAME;
-			cert = new TlsCertificate.from_file(cert_path);
-			var ca_path = cert_dir + CA_FILENAME;
-			var db_type = TlsBackend.get_default().get_file_database_type();
-			ca_db = Object.new(db_type, "anchors", ca_path) as TlsDatabase;
-		}
-
-		public Session start_session() throws Error {
-			var plain_client = new SocketClient();
-			plain_client.set_timeout(TIMEOUT_S);
-			var plain_connection = plain_client.connect(host);
-			var connection = TlsClientConnection.new(plain_connection, host);
-			connection.set_database(ca_db);
-			connection.set_certificate(cert);
-			connection.handshake();
-			return new Session(connection);
-		}
-	}
-
-	private class Session {
-		public signal void received(uint8[] msg);
-
-		private const uint MAX_BATCH_SIZE = 10;
-		private const uint MAX_MSG_LEN = 1024;
-
-		private TlsClientConnection connection;
-
-		public Session(TlsClientConnection connection) {
-			this.connection = connection;
-		}
-
-		public OutgoingMessage? task(AsyncQueue<OutgoingMessage> queue) {
-			for (int i = 0; i < MAX_BATCH_SIZE; ++i) {
-				if (queue.length() == 0)
-					break;
-				var msg = queue.pop();
-				var success = true;
-				success &= send(msg);
-				success &= receive();
-				if (!success)
-					return msg;
-			}
-			return null;
-		}
-
-		private bool send(OutgoingMessage msg) {
-			try {
-				size_t written;
-				connection.output_stream.write_all(msg.content, out written);
-				return true;
-			} catch (IOError _) {
-				return false;
-			}
-		}
-
-		private bool receive() {
-			try {
-				var buffer = new uint8[MAX_MSG_LEN];
-				var len = connection.input_stream.read(buffer);
-				if (len <= 0)
-					return false;
-				received(buffer[0:len]);
-				return true;
-			} catch (IOError _) {
-				return false;
-			}
-		}
-	}
-
-	private class OutgoingMessage {
-		public uint8[] content { get; private set; }
-
-		private const uint MAX_FAIL_COUNT = 4;
-
-		private uint fail_count;
-
-		public OutgoingMessage(owned uint8[] content) {
-			this.content = (owned)content;
-			fail_count = 0;
-		}
-
-		public void has_failed() {
-			++fail_count;
-		}
-
-		public bool should_retry() {
-			return fail_count < MAX_FAIL_COUNT;
-		}
 	}
 }
diff --git a/client/src/meson.build b/client/src/meson.build
index 734da92..69f5240 100644
--- a/client/src/meson.build
+++ b/client/src/meson.build
@@ -14,6 +14,7 @@ lib = library(
     'connection.vala',
     'der.vala',
     'main_window.vala',
+    'session_manager.vala',
   ) + resources,
   dependencies: [gtk_dep],
   vala_vapi: 'study-system-client.vapi',
diff --git a/client/src/session_manager.vala b/client/src/session_manager.vala
new file mode 100644
index 0000000..8541880
--- /dev/null
+++ b/client/src/session_manager.vala
@@ -0,0 +1,167 @@
+namespace StudySystemClient {
+	public class SessionManager {
+		public delegate void ReceiveCallback(uint8[] msg);
+
+		private const uint INIT_RECONNECT_WAIT_MS = 500;
+		private const uint MAX_RECONNECT_WAIT_MS = 60000;
+		private const double RECONNECT_BACKOFF = 1.6;
+
+		private SessionFactory session_factory;
+		private ReceiveCallback receive_callback;
+		private Session? session;
+		private AsyncQueue<OutgoingMessage> queue;
+		private uint reconnect_wait_ms;
+
+		public SessionManager(SessionFactory session_factory,
+							  owned ReceiveCallback receive_callback) {
+			this.session_factory = session_factory;
+			this.receive_callback = (owned) receive_callback;
+			this.session = null;
+			queue = new AsyncQueue<OutgoingMessage>();
+			reconnect_wait_ms = INIT_RECONNECT_WAIT_MS;
+		}
+
+		public void send(uint8[] msg) {
+			queue.push(new OutgoingMessage(msg));
+		}
+
+		public void task() {
+			if (session != null) {
+				var failed_msg = session.task(queue);
+				if (failed_msg != null)
+					handle_failed_msg(failed_msg);
+			} else {
+				try_start_session();
+			}
+		}
+
+		private void handle_failed_msg(OutgoingMessage msg) {
+			msg.has_failed();
+			if (msg.should_retry())
+				queue.push(msg);
+			session = null;
+		}
+
+		private void try_start_session() {
+			try {
+				session = session_factory.start_session();
+				session.received.connect(
+					(msg) => receive_callback(msg));
+				reconnect_wait_ms = INIT_RECONNECT_WAIT_MS;
+			} catch (Error _) {
+				Thread.usleep(1000 * reconnect_wait_ms);
+				update_reconnect_wait();
+			}
+		}
+
+		private void update_reconnect_wait() {
+			var new_wait = RECONNECT_BACKOFF * reconnect_wait_ms;
+			if (new_wait < MAX_RECONNECT_WAIT_MS)
+				reconnect_wait_ms = (uint)new_wait;
+			else
+				reconnect_wait_ms = MAX_RECONNECT_WAIT_MS;
+		}
+	}
+
+	public class SessionFactory {
+		private const string CA_FILENAME = "/ca.pem";
+		private const string CERT_FILENAME = "/client.pem";
+		private const uint TIMEOUT_S = 1;
+
+		private InetSocketAddress host;
+		private TlsCertificate cert;
+		private TlsDatabase ca_db;
+
+		public SessionFactory(InetAddress host_addr, uint16 host_port,
+							  string cert_dir) throws Error {
+			host = new InetSocketAddress(host_addr, host_port);
+			var cert_path = cert_dir + CERT_FILENAME;
+			cert = new TlsCertificate.from_file(cert_path);
+			var ca_path = cert_dir + CA_FILENAME;
+			var db_type = TlsBackend.get_default().get_file_database_type();
+			ca_db = Object.new(db_type, "anchors", ca_path) as TlsDatabase;
+		}
+
+		internal Session start_session() throws Error {
+			var plain_client = new SocketClient();
+			plain_client.set_timeout(TIMEOUT_S);
+			var plain_connection = plain_client.connect(host);
+			var connection = TlsClientConnection.new(plain_connection, host);
+			connection.set_database(ca_db);
+			connection.set_certificate(cert);
+			connection.handshake();
+			return new Session(connection);
+		}
+	}
+
+	private class Session {
+		public signal void received(uint8[] msg);
+
+		private const uint MAX_BATCH_SIZE = 10;
+		private const uint MAX_MSG_LEN = 1024;
+
+		private TlsClientConnection connection;
+
+		public Session(TlsClientConnection connection) {
+			this.connection = connection;
+		}
+
+		public OutgoingMessage? task(AsyncQueue<OutgoingMessage> queue) {
+			for (int i = 0; i < MAX_BATCH_SIZE; ++i) {
+				if (queue.length() == 0)
+					break;
+				var msg = queue.pop();
+				var success = true;
+				success &= send(msg);
+				success &= receive();
+				if (!success)
+					return msg;
+			}
+			return null;
+		}
+
+		private bool send(OutgoingMessage msg) {
+			try {
+				size_t written;
+				connection.output_stream.write_all(msg.content, out written);
+				return true;
+			} catch (IOError _) {
+				return false;
+			}
+		}
+
+		private bool receive() {
+			try {
+				var buffer = new uint8[MAX_MSG_LEN];
+				var len = connection.input_stream.read(buffer);
+				if (len <= 0)
+					return false;
+				received(buffer[0:len]);
+				return true;
+			} catch (IOError _) {
+				return false;
+			}
+		}
+	}
+
+	private class OutgoingMessage {
+		public uint8[] content { get; private set; }
+
+		private const uint MAX_FAIL_COUNT = 4;
+
+		private uint fail_count;
+
+		public OutgoingMessage(owned uint8[] content) {
+			this.content = (owned)content;
+			fail_count = 0;
+		}
+
+		public void has_failed() {
+			++fail_count;
+		}
+
+		public bool should_retry() {
+			return fail_count < MAX_FAIL_COUNT;
+		}
+	}
+}
\ No newline at end of file