Added simple DNS viewer

app/build.gradle

@@ -161,6 +161,7 @@ dependencies {
 
     // https://javaee.github.io/javamail/
     // https://projects.eclipse.org/projects/ee4j.javamail
+    // https://mvnrepository.com/artifact/com.sun.mail
     implementation "com.sun.mail:android-mail:$javamail_version"
     implementation "com.sun.mail:android-activation:$javamail_version"
 

app/src/main/AndroidManifest.xml

@@ -160,6 +160,24 @@
             </intent-filter>
         </activity>
 
+        <activity
+            android:name=".ActivityDSN"
+            android:exported="true"
+            android:icon="@mipmap/ic_launcher"
+            android:label="@string/app_name">
+
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+
+                <category android:name="android.intent.category.BROWSABLE" />
+                <category android:name="android.intent.category.DEFAULT" />
+
+                <data android:scheme="content" />
+                <data android:mimeType="message/disposition-notification" />
+                <data android:host="*" />
+            </intent-filter>
+        </activity>
+
         <service android:name=".ServiceSynchronize" />
 
         <service android:name=".ServiceSend" />

app/src/main/java/eu/faircode/email/ActivityDSN.java

@@ -0,0 +1,93 @@
+package eu.faircode.email;
+
+import android.content.ContentResolver;
+import android.content.Context;
+import android.content.res.AssetFileDescriptor;
+import android.net.Uri;
+import android.os.Bundle;
+import android.view.View;
+import android.widget.TextView;
+
+import com.google.android.material.snackbar.Snackbar;
+
+import java.io.BufferedInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+
+import androidx.constraintlayout.widget.Group;
+
+public class ActivityDSN extends ActivityBase {
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        getSupportActionBar().setSubtitle("DSN");
+        setContentView(R.layout.activity_dsn);
+
+        final TextView tvHeaders = findViewById(R.id.tvHeaders);
+        final ContentLoadingProgressBar pbWait = findViewById(R.id.pbWait);
+        final Group grpReady = findViewById(R.id.grpReady);
+
+        grpReady.setVisibility(View.GONE);
+
+        Uri uri = getIntent().getData();
+        if (uri == null) {
+            pbWait.setVisibility(View.GONE);
+            return;
+        } else
+            pbWait.setVisibility(View.VISIBLE);
+
+        Log.i("Disposition uri=" + uri);
+
+        Bundle args = new Bundle();
+        args.putParcelable("uri", uri);
+
+        new SimpleTask<Result>() {
+            @Override
+            protected void onPostExecute(Bundle args) {
+                pbWait.setVisibility(View.GONE);
+            }
+
+            @Override
+            protected Result onExecute(Context context, Bundle args) throws Throwable {
+                Uri uri = args.getParcelable("uri");
+
+                if ("file".equals(uri.getScheme()))
+                    throw new IllegalArgumentException(context.getString(R.string.title_no_stream));
+
+                Result result = new Result();
+
+                ContentResolver resolver = context.getContentResolver();
+                AssetFileDescriptor descriptor = resolver.openTypedAssetFileDescriptor(uri, "*/*", null);
+                try (InputStream is = new BufferedInputStream(descriptor.createInputStream())) {
+                    ByteArrayOutputStream bos = new ByteArrayOutputStream();
+                    byte[] buffer = new byte[1024];
+                    int length;
+                    while ((length = is.read(buffer)) != -1)
+                        bos.write(buffer, 0, length);
+                    result.headers = bos.toString("UTF-8");
+                }
+
+                return result;
+            }
+
+            @Override
+            protected void onExecuted(Bundle args, Result result) {
+                tvHeaders.setText(result.headers);
+                grpReady.setVisibility(View.VISIBLE);
+            }
+
+            @Override
+            protected void onException(Bundle args, Throwable ex) {
+                if (ex instanceof IllegalArgumentException)
+                    Snackbar.make(findViewById(android.R.id.content), ex.getMessage(), Snackbar.LENGTH_LONG).show();
+                else
+                    Helper.unexpectedError(ActivityDSN.this, ActivityDSN.this, ex);
+            }
+        }.execute(this, args, "disposition:decode");
+    }
+
+    private class Result {
+        String headers;
+    }
+}

app/src/main/res/layout/activity_dsn.xml

@@ -0,0 +1,44 @@
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:orientation="vertical"
+    tools:context=".ActivityDSN">
+
+    <androidx.constraintlayout.widget.ConstraintLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content">
+
+        <TextView
+            android:id="@+id/tvHeaders"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="3dp"
+            android:fontFamily="monospace"
+            android:minHeight="60dp"
+            android:text="Headers"
+            android:textAppearance="@style/TextAppearance.AppCompat.Small"
+            android:textIsSelectable="true"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <eu.faircode.email.ContentLoadingProgressBar
+            android:id="@+id/pbWait"
+            style="@style/Base.Widget.AppCompat.ProgressBar"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:indeterminate="true"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <androidx.constraintlayout.widget.Group
+            android:id="@+id/grpReady"
+            android:layout_width="0dp"
+            android:layout_height="0dp"
+            app:constraint_referenced_ids="tvHeaders" />
+    </androidx.constraintlayout.widget.ConstraintLayout>
+</ScrollView>