From 40f6d425a4429b16936cc8bb4900a23c3362a123 Mon Sep 17 00:00:00 2001
From: Xavier Del Campo Romero <xavi.dcr@tutanota.com>
Date: Sun, 7 Jan 2024 23:49:03 +0100
Subject: WIP

---
 .gitignore                        |   1 +
 AndroidManifest.xml               |  31 +++++++-
 HelloWorld.java                   |  34 ---------
 Makefile                          |  48 +++++++-----
 res/layout/activity_directory.xml |  45 +++++++++++
 res/layout/activity_login.xml     |  93 +++++++++++++++++++++++
 res/layout/activity_main.xml      |  22 +++++-
 src/org/slcl/Directory.java       |  48 ++++++++++++
 src/org/slcl/InternalFile.java    |  38 ++++++++++
 src/org/slcl/LoginActivity.java   | 146 +++++++++++++++++++++++++++++++++++
 src/org/slcl/Main.java            |  93 +++++++++++++++++++++++
 src/org/slcl/core/Cookie.java     | 156 ++++++++++++++++++++++++++++++++++++++
 src/org/slcl/core/Login.java      |  93 +++++++++++++++++++++++
 13 files changed, 791 insertions(+), 57 deletions(-)
 delete mode 100644 HelloWorld.java
 create mode 100644 res/layout/activity_directory.xml
 create mode 100644 res/layout/activity_login.xml
 create mode 100644 src/org/slcl/Directory.java
 create mode 100644 src/org/slcl/InternalFile.java
 create mode 100644 src/org/slcl/LoginActivity.java
 create mode 100644 src/org/slcl/Main.java
 create mode 100644 src/org/slcl/core/Cookie.java
 create mode 100644 src/org/slcl/core/Login.java

diff --git a/.gitignore b/.gitignore
index 49a5af1..b7e7bd2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 *.unsigned
 *.aligned
 R.java
+password.secret
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 242f46d..51c6197 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -1,15 +1,38 @@
 <?xml version="1.0" encoding="utf-8"?>
+
+<!--
+    slcl-android, an Android frontend for slcl
+    Copyright (C) 2023-2024  Xavier Del Campo Romero
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+-->
+
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
- package="helloworld"
+ package="org.slcl"
  versionCode="0"
  versionName="0">
-    <uses-sdk android:minSdkVersion="19"/>
-    <application android:label="Hello World">
-        <activity android:name=".HelloWorld">
+    <uses-permission android:name="android.permission.INTERNET"/>
+    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
+    <uses-sdk android:minSdkVersion="9"/>
+    <application android:label="slcl" android:debuggable="true">
+        <activity android:name=".Main">
              <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
                 <category android:name="android.intent.category.LAUNCHER"/>
              </intent-filter>
         </activity>
+        <activity android:name=".LoginActivity"/>
+        <activity android:name=".Directory"/>
     </application>
 </manifest>
diff --git a/HelloWorld.java b/HelloWorld.java
deleted file mode 100644
index 4f93a65..0000000
--- a/HelloWorld.java
+++ /dev/null
@@ -1,34 +0,0 @@
-import helloworld.R;
-import android.app.Activity;
-import android.os.Bundle;
-import android.widget.TextView;
-import java.io.OutputStream;
-import java.net.URL;
-import javax.net.ssl.HttpsURLConnection;
-
-public class HelloWorld extends Activity {
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-
-        try {
-            Test t = new Test();
-            URL url = new URL("https://slcl.privatedns.org");
-            HttpsURLConnection c = (HttpsURLConnection) url.openConnection();
-
-            t.f();
-
-            c.setFollowRedirects(true);
-
-            OutputStream os = c.getOutputStream();
-            System.out.println("Response code:" + c.getResponseCode());
-        } catch (Exception e) {
-            System.out.println("Exception: " + e.getMessage());
-        }
-
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_main);
-
-        TextView text = (TextView)findViewById(R.id.my_text);
-        text.setText("Hello, world!");
-    }
-}
diff --git a/Makefile b/Makefile
index 76f8162..471ca21 100644
--- a/Makefile
+++ b/Makefile
@@ -1,20 +1,28 @@
 .POSIX:
 .SUFFIXES: .apk .unsigned .aligned
 
-PROJECT = helloworld
+PROJECT = org.slcl
 ANDROIDSDK = /usr/lib/android-sdk
 DX = $(ANDROIDSDK)/build-tools/debian/dx
 MANIFEST = AndroidManifest.xml
 PLATFORM = $(ANDROIDSDK)/platforms/android-23/android.jar
 OBJECTS = \
-	HelloWorld.class \
-	Test.class
+	src/org/slcl/core/Cookie.class \
+	src/org/slcl/core/Login.class \
+	src/org/slcl/Directory.class \
+	src/org/slcl/InternalFile.class \
+	src/org/slcl/Main.class
 RESOURCES = \
+	res/layout/activity_directory.xml \
 	res/layout/activity_main.xml
-R = helloworld/R.java
+R = src/org/slcl/R.java
+PASS = password.secret
+DNAME = "cn=slcl, ou=slcl, o=slcl, c=ES"
 
 # Resources:
 # https://www.hanshq.net/command-line-android.html
+# https://unix.stackexchange.com/questions/230673/how-to-generate-a-random-string
+# https://stuff.mit.edu/afs/sipb/project/android/docs/guide/topics/resources/layout-resource.html#layoutvalues
 
 all: $(PROJECT).apk
 
@@ -24,20 +32,23 @@ $(PROJECT).apk: keystore.jks
 	apksigner sign \
 		--ks keystore.jks \
 		--ks-key-alias androidkey \
-		--ks-pass pass:android \
-		--key-pass pass:android \
+		--ks-pass file:$(PASS) \
 		--out $@ $<
 
-keystore.jks:
-	keytool \
+keystore.jks: $(PASS)
+	(for i in 1 2; do cat $(PASS); done; echo) \
+		| keytool \
 		-genkeypair \
+		-dname $(DNAME) \
 		-keystore $@ \
 		-alias androidkey \
-		-validity 10000 \
 		-keyalg RSA \
-		-keysize 4096 \
-		-storepass android \
-		-keypass android
+		-keysize 4096
+
+$(PASS):
+	(LC_ALL=C \
+		tr -dc 'A-Za-z0-9!"#$$%&'\''()*+,-./:;<=>?@[\]^_`{|}~' \
+		< /dev/urandom | head -c 100; echo) > $(PASS)
 
 .unsigned.aligned:
 	zipalign -f -p 4 $< $@
@@ -45,19 +56,20 @@ keystore.jks:
 $(PROJECT).unsigned: dex/classes.dex $(MANIFEST)
 	aapt package -f -F $@ -I $(PLATFORM) -M $(MANIFEST) -S res dex
 
-dex/classes.dex: $(OBJECTS) $(MANIFEST)
+dex/classes.dex: .build $(MANIFEST)
 	mkdir -p dex
-	$(DX) --dex --output=$@ $(OBJECTS)
+	$(DX) --dex --min-sdk-version=9 --output=$@ src
 
-$(OBJECTS): $(OBJECTS:.class=.java) $(R)
-	javac -bootclasspath $(PLATFORM) -source 1.7 $(OBJECTS:.class=.java)
+.build: $(OBJECTS:.class=.java) $(R)
+	javac -bootclasspath $(PLATFORM) -source 1.7 -sourcepath src $(OBJECTS:.class=.java)
+	touch $@
 
 $(R): $(MANIFEST) $(RESOURCES)
-	aapt package -f -m -S res -M $(MANIFEST) -I $(PLATFORM) -J .
+	aapt package -f -m -S res -M $(MANIFEST) -I $(PLATFORM) -J src
 
 clean:
 	rm -f $(R) $(OBJECTS) $(PROJECT).unsigned \
 		$(PROJECT).aligned $(PROJECT).apk.idsig dex/classes.dex
 
 distclean: clean
-	rm -rf dex/ *.apk keystore.jks
+	rm -rf dex/ *.apk keystore.jks $(PASS)
diff --git a/res/layout/activity_directory.xml b/res/layout/activity_directory.xml
new file mode 100644
index 0000000..cd6db5b
--- /dev/null
+++ b/res/layout/activity_directory.xml
@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<!--
+    slcl-android, an Android frontend for slcl
+    Copyright (C) 2023-2024  Xavier Del Campo Romero
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+-->
+
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:gravity="center"
+    android:orientation="vertical">
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="slcl, a simple and lightweight cloud"/>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="URL:"/>
+
+    <LinearLayout
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:orientation="horizontal">
+
+    </LinearLayout>
+</LinearLayout>
diff --git a/res/layout/activity_login.xml b/res/layout/activity_login.xml
new file mode 100644
index 0000000..835a828
--- /dev/null
+++ b/res/layout/activity_login.xml
@@ -0,0 +1,93 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<!--
+    slcl-android, an Android frontend for slcl
+    Copyright (C) 2023-2024  Xavier Del Campo Romero
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+-->
+
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:gravity="center"
+    android:orientation="vertical">
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="slcl, a simple and lightweight cloud"/>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="URL:"/>
+
+    <LinearLayout
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:orientation="horizontal">
+
+            <CheckBox
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:text="HTTPS"
+                android:checked="true"
+                android:id="@+id/https"/>
+
+            <EditText
+                android:layout_width="250sp"
+                android:layout_height="wrap_content"
+                android:singleLine="true"
+                android:id="@+id/url">
+                <requestFocus/>
+            </EditText>
+
+    </LinearLayout>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Username:"/>
+
+    <EditText
+        android:layout_width="250sp"
+        android:layout_height="wrap_content"
+        android:singleLine="true"
+        android:id="@+id/username">
+    </EditText>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Password:"/>
+
+    <EditText
+        android:layout_width="250sp"
+        android:layout_height="wrap_content"
+        android:id="@+id/password"
+        android:inputType="textPassword"/>
+
+    <Button android:id="@+id/button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Login"/>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:id="@+id/error"/>
+</LinearLayout>
diff --git a/res/layout/activity_main.xml b/res/layout/activity_main.xml
index 2f67c50..1f3d7ae 100644
--- a/res/layout/activity_main.xml
+++ b/res/layout/activity_main.xml
@@ -1,4 +1,23 @@
 <?xml version="1.0" encoding="utf-8"?>
+
+<!--
+    slcl-android, an Android frontend for slcl
+    Copyright (C) 2023-2024  Xavier Del Campo Romero
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+-->
+
 <LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
@@ -9,5 +28,6 @@
     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:id="@+id/my_text"/>
+        android:text="slcl, a simple and lightweight cloud"/>
+
 </LinearLayout>
diff --git a/src/org/slcl/Directory.java b/src/org/slcl/Directory.java
new file mode 100644
index 0000000..495a3f5
--- /dev/null
+++ b/src/org/slcl/Directory.java
@@ -0,0 +1,48 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl;
+
+import java.net.URLEncoder;
+import java.io.IOException;
+import android.app.Activity;
+import android.app.ProgressDialog;
+import android.content.Intent;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.text.Editable;
+import android.view.View;
+import android.widget.Button;
+import android.widget.CheckBox;
+import android.widget.EditText;
+import android.widget.TextView;
+
+public class Directory extends Activity {
+    public static final String EXTRA_ID = "cookie";
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_directory);
+
+        final Intent intent = getIntent();
+        final String cookie = intent.getStringExtra(EXTRA_ID);
+
+        System.out.println(cookie);
+    }
+}
diff --git a/src/org/slcl/InternalFile.java b/src/org/slcl/InternalFile.java
new file mode 100644
index 0000000..db41576
--- /dev/null
+++ b/src/org/slcl/InternalFile.java
@@ -0,0 +1,38 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl;
+
+import java.io.File;
+import android.content.Context;
+
+final public class InternalFile {
+    final File f;
+
+    InternalFile(final Context c, final String path)
+    {
+        final File dir = c.getFilesDir();
+
+        f = new File(dir, path);
+    }
+
+    public File getFile()
+    {
+        return f;
+    }
+}
diff --git a/src/org/slcl/LoginActivity.java b/src/org/slcl/LoginActivity.java
new file mode 100644
index 0000000..79e2ed4
--- /dev/null
+++ b/src/org/slcl/LoginActivity.java
@@ -0,0 +1,146 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl;
+
+import org.slcl.core.Cookie;
+import org.slcl.core.Login;
+import org.slcl.Directory;
+import org.slcl.InternalFile;
+import java.net.URLEncoder;
+import java.io.IOException;
+import android.app.Activity;
+import android.app.ProgressDialog;
+import android.content.Context;
+import android.content.Intent;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.text.Editable;
+import android.view.View;
+import android.widget.Button;
+import android.widget.CheckBox;
+import android.widget.EditText;
+import android.widget.TextView;
+
+public final class LoginActivity extends Activity {
+
+    private class LoginParams {
+        public LoginParams(final boolean https, String url,
+            final String username, final String password)
+        {
+            this.https = https;
+            this.username = username;
+            this.url = url;
+            this.password = password;
+        }
+
+        final boolean https;
+        final String url, username, password;
+    }
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState)
+    {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_login);
+
+        Button button = (Button)findViewById(R.id.button);
+
+        button.setOnClickListener(new View.OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                final EditText url = (EditText)findViewById(R.id.url);
+                final EditText username = (EditText)findViewById(R.id.username);
+                final EditText password = (EditText)findViewById(R.id.password);
+                final CheckBox https = (CheckBox)findViewById(R.id.https);
+
+                url.setText("192.168.1.180:50683");
+                username.setText("a");
+                password.setText("a");
+                https.setChecked(false);
+
+                try {
+                    final String urlstr = url.getText().toString();
+                    final String encusername = URLEncoder.encode(
+                        username.getText().toString(), "UTF-8");
+                    final String encpassword = URLEncoder.encode(
+                        password.getText().toString(), "UTF-8");
+
+                    final LoginTask t = new LoginTask();
+                    LoginParams p = new LoginParams(https.isChecked(),
+                        urlstr, encusername, encpassword);
+
+                    t.execute(p);
+                }
+                catch (final IOException e) {
+                    //error.setText("Exception: " + e.getMessage());
+                }
+            }
+        });
+    }
+
+    // https://stackoverflow.com/questions/6053602/what-arguments-are-passed-into-asynctaskarg1-arg2-arg3
+    private final class LoginTask
+        extends AsyncTask<LoginParams, String, String>
+    {
+        ProgressDialog dialog;
+
+        @Override
+        protected void onPreExecute()
+        {
+            dialog = dialog.show(LoginActivity.this, "ProgressDialog",
+                "Logging into server");
+        }
+
+        @Override
+        protected String doInBackground(final LoginParams... params)
+        {
+            try {
+                final LoginParams p = params[0];
+                final Login l = new Login();
+                final String cookie = l.login(p.https, p.url, p.username,
+                    p.password);
+                final InternalFile f = new InternalFile(
+                        getApplicationContext(), "login");
+                final Cookie c = new Cookie(p.username, cookie);
+
+                c.store(f.getFile());
+                return "";
+            } catch (final IOException e) {
+                System.out.println(e.getMessage());
+                return e.getMessage();
+            }
+        }
+
+        @Override
+        protected void onProgressUpdate(final String... text)
+        {
+        }
+
+        @Override
+        protected void onPostExecute(final String result)
+        {
+            Intent intent = new Intent(LoginActivity.this, Directory.class);
+
+            dialog.dismiss();
+            startActivity(intent);
+            // TODO: review errors.
+            //error.setText("Exception: " + e.getMessage());
+        }
+    }
+}
diff --git a/src/org/slcl/Main.java b/src/org/slcl/Main.java
new file mode 100644
index 0000000..8ac8c55
--- /dev/null
+++ b/src/org/slcl/Main.java
@@ -0,0 +1,93 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl;
+
+import org.slcl.LoginActivity;
+import org.slcl.Directory;
+import org.slcl.core.Cookie;
+import java.io.IOException;
+import android.app.Activity;
+import android.app.ProgressDialog;
+import android.content.Context;
+import android.content.Intent;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.text.Editable;
+import android.view.View;
+
+public final class Main extends Activity {
+    @Override
+    protected void onCreate(Bundle savedInstanceState)
+    {
+        final LoadTask t = new LoadTask();
+
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_main);
+        t.execute();
+    }
+
+    private final class LoadTask extends AsyncTask<String, String, Cookie>
+    {
+        ProgressDialog dialog;
+
+        @Override
+        protected void onPreExecute()
+        {
+            dialog = dialog.show(Main.this, "ProgressDialog",
+                "Retrieving credentials");
+        }
+
+        @Override
+        protected Cookie doInBackground(final String... args)
+        {
+            try {
+                final InternalFile f = new InternalFile(
+                    getApplicationContext(), "login");
+                final Cookie c = new Cookie(f.getFile());
+
+                return c;
+            } catch (final IOException e) {
+                System.out.println(e.getMessage());
+                return null;
+            }
+        }
+
+        @Override
+        protected void onProgressUpdate(final String... params)
+        {
+        }
+
+        @Override
+        protected void onPostExecute(final Cookie cookie)
+        {
+            final Intent intent;
+
+            if (cookie == null) {
+                intent = new Intent(Main.this, LoginActivity.class);
+            } else {
+                intent = new Intent(Main.this, Directory.class);
+                // TODO: split cookie with ';' (expiration date, etc.).
+                intent.putExtra(Directory.EXTRA_ID, cookie.getCookie());
+            }
+
+            dialog.dismiss();
+            startActivity(intent);
+        }
+    }
+}
diff --git a/src/org/slcl/core/Cookie.java b/src/org/slcl/core/Cookie.java
new file mode 100644
index 0000000..86f64b5
--- /dev/null
+++ b/src/org/slcl/core/Cookie.java
@@ -0,0 +1,156 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl.core;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.InputStreamReader;
+import java.io.IOException;
+import java.text.ParsePosition;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.List;
+
+public final class Cookie {
+    final String username, cookie;
+    final CookieDate date;
+
+    private final class Results {
+        final String username, cookie;
+        final CookieDate date;
+
+        Results(String username, String cookie, final CookieDate date)
+        {
+            this.username = username;
+            this.cookie = cookie;
+            this.date = date;
+        }
+    }
+
+    public Cookie(final File f)
+        throws IOException {
+        final FileInputStream fis = new FileInputStream(f);
+        final InputStreamReader ir = new InputStreamReader(fis);
+        final BufferedReader r = new BufferedReader(ir);
+        final Results res = from_data(null, r.readLine());
+
+        username = res.username;
+        cookie = res.cookie;
+        date = res.date;
+        fis.close();
+    }
+
+    private final class CookieDate {
+        final private String FMT = "EEE, dd MMM yyyy hh:mm:ss z";
+        Date date;
+
+        public CookieDate(final String[] tokens) throws IOException
+        {
+            for (int i = 1; i < tokens.length; i++) {
+                final String[] date_tokens = tokens[i].split("=");
+
+                if (date_tokens.length != 2) {
+                    continue;
+                }
+
+                final String header = date_tokens[0].trim();
+
+                if (!header.equalsIgnoreCase("Expires")) {
+                    continue;
+                }
+
+                ParsePosition pos = new ParsePosition(0);
+                final SimpleDateFormat fmt = new SimpleDateFormat(FMT);
+                final Date d = fmt.parse(date_tokens[1], pos);
+
+                if (d != null) {
+                    // TODO: check pos.
+                    date = d;
+                    return;
+                }
+            }
+
+            throw new IOException("missing expiration date");
+        }
+
+        public String toString()
+        {
+            final SimpleDateFormat fmt = new SimpleDateFormat(FMT);
+
+            return fmt.format(date, null, null).toString();
+        }
+
+        public Date getDate() {
+            return date;
+        }
+    }
+
+    private Results from_data(final String exp_username, final String data)
+        throws IOException
+    {
+        final int sep = data.indexOf('=');
+
+        if (sep <= 0) {
+            throw new IOException("expected key=value format");
+        }
+
+        final String username = data.substring(0, sep);
+
+        if (exp_username != null
+            && !username.equals(exp_username)) {
+            throw new IOException("wrong username");
+        }
+
+        final String[] tokens = data.substring(sep + 1).split(";");
+
+        if (tokens.length < 2) {
+            throw new IOException("expected at least two tokens");
+        }
+
+        return new Results(username, tokens[0], new CookieDate(tokens));
+    }
+
+    public Cookie(final String exp_username, final String data)
+        throws IOException
+    {
+        final Results r = from_data(exp_username, data);
+
+        username = r.username;
+        cookie = r.cookie;
+        date = r.date;
+    }
+
+    public void store(final File f) throws IOException
+    {
+        final FileOutputStream fos = new FileOutputStream(f);
+        final String datestr = "Expires=" + date.toString();
+
+        fos.write(cookie.getBytes());
+        fos.write(';');
+        fos.write(datestr.getBytes());
+        fos.write('\n');
+        fos.close();
+    }
+
+    public String getCookie() {
+        return cookie;
+    }
+}
diff --git a/src/org/slcl/core/Login.java b/src/org/slcl/core/Login.java
new file mode 100644
index 0000000..d5b9267
--- /dev/null
+++ b/src/org/slcl/core/Login.java
@@ -0,0 +1,93 @@
+/*
+ * slcl-android, an Android frontend for slcl
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.slcl.core;
+
+import java.io.OutputStream;
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLConnection;
+import java.net.HttpURLConnection;
+import java.util.List;
+import java.util.Map;
+import javax.net.ssl.HttpsURLConnection;
+
+public final class Login {
+    public String login(final boolean https, String url, final String username,
+        final String password) throws IOException {
+
+        if (!url.startsWith("https://") && https) {
+            url = "https://" + url;
+        }
+        else if (!url.startsWith("http://")) {
+            url = "http://" + url;
+        }
+
+        url += "/login";
+
+        final String data = "username=" + username + "&password=" + password;
+
+        URL u = new URL(url);
+        HttpURLConnection c;
+
+        if (https) {
+            c = (HttpsURLConnection)u.openConnection();
+        }
+        else {
+            c = (HttpURLConnection)u.openConnection();
+        }
+
+        c.setRequestMethod("POST");
+        c.setInstanceFollowRedirects(false);
+        c.setReadTimeout(5000);
+
+        OutputStream os = c.getOutputStream();
+
+        os.write(data.getBytes());
+
+        final int code = c.getResponseCode();
+
+        switch (code)
+        {
+            case HttpURLConnection.HTTP_FORBIDDEN:
+                throw new IOException("Forbidden");
+
+            case HttpURLConnection.HTTP_UNAUTHORIZED:
+                throw new IOException("Unauthorized");
+
+            case HttpURLConnection.HTTP_SEE_OTHER:
+            {
+                final Map<String,List<String>> headers = c.getHeaderFields();
+                final List<String> cookies = headers.get("Set-Cookie");
+
+                if (cookies != null) {
+                    if (cookies.size() != 1) {
+                        throw new IOException("Expected only 1 cookie");
+                    }
+
+                    return cookies.toArray(new String[0])[0];
+                } else {
+                    throw new IOException("No Cookie found");
+                }
+            }
+
+            default:
+                throw new IOException("Unexpected HTTP status " + code);
+        }
+    }
+}
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