Added simple DNS viewer

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;
+    }
+}