Unsubscribe redirect

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

@@ -21,7 +21,6 @@ package eu.faircode.email;
 
 import android.app.Dialog;
 import android.content.Context;
-import android.content.DialogInterface;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -34,9 +33,10 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AlertDialog;
 
-import java.io.IOException;
+import java.net.HttpURLConnection;
-import java.io.InputStream;
 import java.net.URL;
+import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 
 import javax.net.ssl.HttpsURLConnection;
 
@@ -87,11 +87,14 @@ public class FragmentDialogUnsubscribe extends FragmentDialogBase {
                     protected String onExecute(Context context, Bundle args) throws Throwable {
                         final String uri = args.getString("uri");
                         final String request = "List-Unsubscribe=One-Click";
-                        Log.i("Unsubscribe request=" + request + " uri=" + uri);
 
                         // https://datatracker.ietf.org/doc/html/rfc8058
 
+                        int redirects = 0;
                         URL url = new URL(uri);
+                        do {
+                            Log.i("Unsubscribe request=" + request + " uri=" + uri);
+
                             HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
                             connection.setRequestMethod("POST");
                             connection.setDoInput(true);
@@ -108,6 +111,20 @@ public class FragmentDialogUnsubscribe extends FragmentDialogBase {
                                 connection.getOutputStream().write(request.getBytes());
 
                                 int status = connection.getResponseCode();
+                                if (status == HttpURLConnection.HTTP_MOVED_PERM ||
+                                        status == HttpURLConnection.HTTP_MOVED_TEMP ||
+                                        status == HttpURLConnection.HTTP_SEE_OTHER ||
+                                        status == 307 /* Temporary redirect */ ||
+                                        status == 308 /* Permanent redirect */) {
+                                    String header = connection.getHeaderField("Location");
+                                    if (header != null) {
+                                        String location = URLDecoder.decode(header, StandardCharsets.UTF_8.name());
+                                        Log.i("Unsubscribe redirect=" + location);
+                                        url = new URL(url, location);
+                                        continue;
+                                    }
+                                }
+
                                 if (status >= 300) {
                                     String error = status + ": " + connection.getResponseMessage();
                                     Log.i("Unsubscribe error=" + error);
@@ -119,6 +136,9 @@ public class FragmentDialogUnsubscribe extends FragmentDialogBase {
                             } finally {
                                 connection.disconnect();
                             }
+                        } while (++redirects <= ConnectionHelper.MAX_REDIRECTS);
+
+                        return null;
                     }
 
                     @Override