FairEmail/openpgp-api/src/main/java/org/openintents/openpgp/util/OpenPgpApi.java

/*
 * Copyright (C) 2014-2015 Dominik Schürmann <dominik@dominikschuermann.de>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.openintents.openpgp.util;


import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.concurrent.atomic.AtomicInteger;

import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Handler;
import android.os.Message;
import android.os.Messenger;
import android.os.ParcelFileDescriptor;
import android.util.Log;

import org.openintents.openpgp.IOpenPgpService2;
import org.openintents.openpgp.OpenPgpError;
import org.openintents.openpgp.util.ParcelFileDescriptorUtil.DataSinkTransferThread;
import org.openintents.openpgp.util.ParcelFileDescriptorUtil.DataSourceTransferThread;


public class OpenPgpApi {

    public static final String TAG = "OpenPgp API";

    public static final String SERVICE_INTENT_2 = "org.openintents.openpgp.IOpenPgpService2";

    /**
     * see CHANGELOG.md
     */
    public static final int API_VERSION = 12;

    /**
     * General extras
     * --------------
     *
     * required extras:
     * int           EXTRA_API_VERSION           (always required)
     *
     * returned extras:
     * int           RESULT_CODE                 (RESULT_CODE_ERROR, RESULT_CODE_SUCCESS or RESULT_CODE_USER_INTERACTION_REQUIRED)
     * OpenPgpError  RESULT_ERROR                (if RESULT_CODE == RESULT_CODE_ERROR)
     * PendingIntent RESULT_INTENT               (if RESULT_CODE == RESULT_CODE_USER_INTERACTION_REQUIRED)
     */

    /**
     * This action performs no operation, but can be used to check if the App has permission
     * to access the API in general, returning a user interaction PendingIntent otherwise.
     * This can be used to trigger the permission dialog explicitly.
     *
     * This action uses no extras.
     */
    public static final String ACTION_CHECK_PERMISSION = "org.openintents.openpgp.action.CHECK_PERMISSION";

    @Deprecated
    public static final String ACTION_SIGN = "org.openintents.openpgp.action.SIGN";

    /**
     * Sign text resulting in a cleartext signature
     * Some magic pre-processing of the text is done to convert it to a format usable for
     * cleartext signatures per RFC 4880 before the text is actually signed:
     * - end cleartext with newline
     * - remove whitespaces on line endings
     *
     * required extras:
     * long          EXTRA_SIGN_KEY_ID           (key id of signing key)
     *
     * optional extras:
     * char[]        EXTRA_PASSPHRASE            (key passphrase)
     */
    public static final String ACTION_CLEARTEXT_SIGN = "org.openintents.openpgp.action.CLEARTEXT_SIGN";

    /**
     * Sign text or binary data resulting in a detached signature.
     * No OutputStream necessary for ACTION_DETACHED_SIGN (No magic pre-processing like in ACTION_CLEARTEXT_SIGN)!
     * The detached signature is returned separately in RESULT_DETACHED_SIGNATURE.
     *
     * required extras:
     * long          EXTRA_SIGN_KEY_ID           (key id of signing key)
     *
     * optional extras:
     * boolean       EXTRA_REQUEST_ASCII_ARMOR   (request ascii armor for detached signature)
     * char[]        EXTRA_PASSPHRASE            (key passphrase)
     *
     * returned extras:
     * byte[]        RESULT_DETACHED_SIGNATURE
     * String        RESULT_SIGNATURE_MICALG     (contains the name of the used signature algorithm as a string)
     */
    public static final String ACTION_DETACHED_SIGN = "org.openintents.openpgp.action.DETACHED_SIGN";

    /**
     * Encrypt
     *
     * required extras:
     * String[]      EXTRA_USER_IDS              (=emails of recipients, if more than one key has a user_id, a PendingIntent is returned via RESULT_INTENT)
     * or
     * long[]        EXTRA_KEY_IDS
     *
     * optional extras:
     * boolean       EXTRA_REQUEST_ASCII_ARMOR   (request ascii armor for output)
     * char[]        EXTRA_PASSPHRASE            (key passphrase)
     * String        EXTRA_ORIGINAL_FILENAME     (original filename to be encrypted as metadata)
     * boolean       EXTRA_ENABLE_COMPRESSION    (enable ZLIB compression, default ist true)
     */
    public static final String ACTION_ENCRYPT = "org.openintents.openpgp.action.ENCRYPT";

    /**
     * Sign and encrypt
     *
     * required extras:
     * String[]      EXTRA_USER_IDS              (=emails of recipients, if more than one key has a user_id, a PendingIntent is returned via RESULT_INTENT)
     * or
     * long[]        EXTRA_KEY_IDS
     *
     * optional extras:
     * long          EXTRA_SIGN_KEY_ID           (key id of signing key)
     * boolean       EXTRA_REQUEST_ASCII_ARMOR   (request ascii armor for output)
     * char[]        EXTRA_PASSPHRASE            (key passphrase)
     * String        EXTRA_ORIGINAL_FILENAME     (original filename to be encrypted as metadata)
     * boolean       EXTRA_ENABLE_COMPRESSION    (enable ZLIB compression, default ist true)
     */
    public static final String ACTION_SIGN_AND_ENCRYPT = "org.openintents.openpgp.action.SIGN_AND_ENCRYPT";

    public static final String ACTION_QUERY_AUTOCRYPT_STATUS = "org.openintents.openpgp.action.QUERY_AUTOCRYPT_STATUS";

    /**
     * Decrypts and verifies given input stream. This methods handles encrypted-only, signed-and-encrypted,
     * and also signed-only input.
     * OutputStream is optional, e.g., for verifying detached signatures!
     *
     * If OpenPgpSignatureResult.getResult() == OpenPgpSignatureResult.RESULT_KEY_MISSING
     * in addition a PendingIntent is returned via RESULT_INTENT to download missing keys.
     * On all other status, in addition a PendingIntent is returned via RESULT_INTENT to open
     * the key view in OpenKeychain.
     *
     * optional extras:
     * byte[]        EXTRA_DETACHED_SIGNATURE    (detached signature)
     *
     * returned extras:
     * OpenPgpSignatureResult   RESULT_SIGNATURE
     * OpenPgpDecryptionResult  RESULT_DECRYPTION
     * OpenPgpDecryptMetadata   RESULT_METADATA
     * String                   RESULT_CHARSET   (charset which was specified in the headers of ascii armored input, if any)
     */
    public static final String ACTION_DECRYPT_VERIFY = "org.openintents.openpgp.action.DECRYPT_VERIFY";

    /**
     * Decrypts the header of an encrypted file to retrieve metadata such as original filename.
     *
     * This does not decrypt the actual content of the file.
     *
     * returned extras:
     * OpenPgpDecryptMetadata   RESULT_METADATA
     * String                   RESULT_CHARSET   (charset which was specified in the headers of ascii armored input, if any)
     */
    public static final String ACTION_DECRYPT_METADATA = "org.openintents.openpgp.action.DECRYPT_METADATA";

    /**
     * Select key id for signing
     *
     * optional extras:
     * String      EXTRA_USER_ID
     *
     * returned extras:
     * long        EXTRA_SIGN_KEY_ID
     */
    public static final String ACTION_GET_SIGN_KEY_ID = "org.openintents.openpgp.action.GET_SIGN_KEY_ID";

    /**
     * Get key ids based on given user ids (=emails)
     *
     * required extras:
     * String[]      EXTRA_USER_IDS
     *
     * returned extras:
     * long[]        RESULT_KEY_IDS
     */
    public static final String ACTION_GET_KEY_IDS = "org.openintents.openpgp.action.GET_KEY_IDS";

    /**
     * This action returns RESULT_CODE_SUCCESS if the OpenPGP Provider already has the key
     * corresponding to the given key id in its database.
     *
     * It returns RESULT_CODE_USER_INTERACTION_REQUIRED if the Provider does not have the key.
     * The PendingIntent from RESULT_INTENT can be used to retrieve those from a keyserver.
     *
     * If an Output stream has been defined the whole public key is returned.
     * required extras:
     * long        EXTRA_KEY_ID
     *
     * optional extras:
     * String      EXTRA_REQUEST_ASCII_ARMOR (request that the returned key is encoded in ASCII Armor)
     */
    public static final String ACTION_GET_KEY = "org.openintents.openpgp.action.GET_KEY";

    /**
     * Backup all keys given by EXTRA_KEY_IDS and if requested their secret parts.
     * The encrypted backup will be written to the OutputStream.
     * The client app has no access to the backup code used to encrypt the backup!
     * This operation always requires user interaction with RESULT_CODE_USER_INTERACTION_REQUIRED!
     *
     * required extras:
     * long[]      EXTRA_KEY_IDS       (keys that should be included in the backup)
     * boolean     EXTRA_BACKUP_SECRET (also backup secret keys)
     */
    public static final String ACTION_BACKUP = "org.openintents.openpgp.action.BACKUP";

    /**
     * Update the status of some Autocrypt peer, identified by their peer id.
     *
     * required extras:
     * String                  EXTRA_AUTOCRYPT_PEER_ID       (autocrypt peer id to update)
     * AutocryptPeerUpdate     EXTRA_AUTOCRYPT_PEER_UPDATE   (actual peer update)
     */
    public static final String ACTION_UPDATE_AUTOCRYPT_PEER = "org.openintents.openpgp.action.UPDATE_AUTOCRYPT_PEER";

    /* Intent extras */
    public static final String EXTRA_API_VERSION = "api_version";

    // ACTION_DETACHED_SIGN, ENCRYPT, SIGN_AND_ENCRYPT, DECRYPT_VERIFY
    // request ASCII Armor for output
    // OpenPGP Radix-64, 33 percent overhead compared to binary, see http://tools.ietf.org/html/rfc4880#page-53)
    public static final String EXTRA_REQUEST_ASCII_ARMOR = "ascii_armor";

    // ACTION_DETACHED_SIGN
    public static final String RESULT_DETACHED_SIGNATURE = "detached_signature";
    public static final String RESULT_SIGNATURE_MICALG = "signature_micalg";

    // ENCRYPT, SIGN_AND_ENCRYPT, QUERY_AUTOCRYPT_STATUS
    public static final String EXTRA_USER_IDS = "user_ids";
    public static final String EXTRA_KEY_IDS = "key_ids";
    public static final String EXTRA_KEY_IDS_SELECTED = "key_ids_selected";
    public static final String EXTRA_SIGN_KEY_ID = "sign_key_id";

    public static final String RESULT_KEYS_CONFIRMED = "keys_confirmed";
    public static final String RESULT_AUTOCRYPT_STATUS = "autocrypt_status";
    public static final int AUTOCRYPT_STATUS_UNAVAILABLE = 0;
    public static final int AUTOCRYPT_STATUS_DISCOURAGE = 1;
    public static final int AUTOCRYPT_STATUS_AVAILABLE = 2;
    public static final int AUTOCRYPT_STATUS_MUTUAL = 3;

    // optional extras:
    public static final String EXTRA_PASSPHRASE = "passphrase";
    public static final String EXTRA_ORIGINAL_FILENAME = "original_filename";
    public static final String EXTRA_ENABLE_COMPRESSION = "enable_compression";
    public static final String EXTRA_OPPORTUNISTIC_ENCRYPTION = "opportunistic";

    // GET_SIGN_KEY_ID
    public static final String EXTRA_USER_ID = "user_id";
    public static final String EXTRA_PRESELECT_KEY_ID = "preselect_key_id";
    public static final String EXTRA_SHOW_AUTOCRYPT_HINT = "show_autocrypt_hint";

    // GET_KEY
    public static final String EXTRA_KEY_ID = "key_id";
    public static final String EXTRA_MINIMIZE = "minimize";
    public static final String EXTRA_MINIMIZE_USER_ID = "minimize_user_id";
    public static final String RESULT_KEY_IDS = "key_ids";

    // AUTOCRYPT_KEY_TRANSFER
    public static final String ACTION_AUTOCRYPT_KEY_TRANSFER = "autocrypt_key_transfer";

    // BACKUP
    public static final String EXTRA_BACKUP_SECRET = "backup_secret";

    /* Service Intent returns */
    public static final String RESULT_CODE = "result_code";

    // get actual error object from RESULT_ERROR
    public static final int RESULT_CODE_ERROR = 0;
    // success!
    public static final int RESULT_CODE_SUCCESS = 1;
    // get PendingIntent from RESULT_INTENT, start PendingIntent with startIntentSenderForResult,
    // and execute service method again in onActivityResult
    public static final int RESULT_CODE_USER_INTERACTION_REQUIRED = 2;

    public static final String RESULT_ERROR = "error";
    public static final String RESULT_INTENT = "intent";

    // DECRYPT_VERIFY
    public static final String EXTRA_DETACHED_SIGNATURE = "detached_signature";
    public static final String EXTRA_PROGRESS_MESSENGER = "progress_messenger";
    public static final String EXTRA_DATA_LENGTH = "data_length";
    public static final String EXTRA_DECRYPTION_RESULT = "decryption_result";
    public static final String EXTRA_SENDER_ADDRESS = "sender_address";
    public static final String EXTRA_SUPPORT_OVERRIDE_CRYPTO_WARNING = "support_override_crpto_warning";
    public static final String RESULT_SIGNATURE = "signature";
    public static final String RESULT_DECRYPTION = "decryption";
    public static final String RESULT_METADATA = "metadata";
    public static final String RESULT_INSECURE_DETAIL_INTENT = "insecure_detail_intent";
    public static final String RESULT_OVERRIDE_CRYPTO_WARNING = "override_crypto_warning";
    // This will be the charset which was specified in the headers of ascii armored input, if any
    public static final String RESULT_CHARSET = "charset";

    // UPDATE_AUTOCRYPT_PEER
    public static final String EXTRA_AUTOCRYPT_PEER_ID = "autocrypt_peer_id";
    public static final String EXTRA_AUTOCRYPT_PEER_UPDATE = "autocrypt_peer_update";
    public static final String EXTRA_AUTOCRYPT_PEER_GOSSIP_UPDATES = "autocrypt_peer_gossip_updates";

    // INTERNAL, must not be used
    public static final String EXTRA_CALL_UUID1 = "call_uuid1";
    public static final String EXTRA_CALL_UUID2 = "call_uuid2";

    IOpenPgpService2 mService;
    Context mContext;
    final AtomicInteger mPipeIdGen = new AtomicInteger();

    public OpenPgpApi(Context context, IOpenPgpService2 service) {
        this.mContext = context;
        this.mService = service;
    }

    public interface IOpenPgpCallback {
        void onReturn(final Intent result);
    }

    public interface IOpenPgpSinkResultCallback<T> {
        void onProgress(int current, int max);
        void onReturn(final Intent result, T sinkResult);
    }

    public interface CancelableBackgroundOperation {
        void cancelOperation();
    }

    private class OpenPgpSourceSinkAsyncTask<T> extends AsyncTask<Void, Integer, OpenPgpDataResult<T>>
            implements CancelableBackgroundOperation {
        Intent data;
        OpenPgpDataSource dataSource;
        OpenPgpDataSink<T> dataSink;
        IOpenPgpSinkResultCallback<T> callback;

        private OpenPgpSourceSinkAsyncTask(Intent data, OpenPgpDataSource dataSource,
                OpenPgpDataSink<T> dataSink, IOpenPgpSinkResultCallback<T> callback) {
            this.data = data;
            this.dataSource = dataSource;
            this.dataSink = dataSink;
            this.callback = callback;
        }

        @Override
        protected OpenPgpDataResult<T> doInBackground(Void... unused) {
            return executeApi(data, dataSource, dataSink);
        }

        protected void onPostExecute(OpenPgpDataResult<T> result) {
            callback.onReturn(result.apiResult, result.sinkResult);
        }

        @Override
        public void cancelOperation() {
            cancel(true);
            if (dataSource != null) {
                dataSource.cancel();
            }
        }
    }

    class OpenPgpAsyncTask extends AsyncTask<Void, Integer, Intent> {
        Intent data;
        InputStream is;
        OutputStream os;
        IOpenPgpCallback callback;

        private OpenPgpAsyncTask(Intent data, InputStream is, OutputStream os, IOpenPgpCallback callback) {
            this.data = data;
            this.is = is;
            this.os = os;
            this.callback = callback;
        }

        @Override
        protected Intent doInBackground(Void... unused) {
            return executeApi(data, is, os);
        }

        protected void onPostExecute(Intent result) {
            callback.onReturn(result);
        }
    }

    public <T> CancelableBackgroundOperation executeApiAsync(Intent data, OpenPgpDataSource dataSource,
            OpenPgpDataSink<T> dataSink, final IOpenPgpSinkResultCallback<T> callback) {
        Messenger messenger = new Messenger(new Handler(new Handler.Callback() {
            @Override
            public boolean handleMessage(Message message) {
                callback.onProgress(message.arg1, message.arg2);
                return true;
            }
        }));
        data.putExtra(EXTRA_PROGRESS_MESSENGER, messenger);

        OpenPgpSourceSinkAsyncTask<T> task = new OpenPgpSourceSinkAsyncTask<>(data, dataSource, dataSink, callback);

        // don't serialize async tasks!
        // http://commonsware.com/blog/2012/04/20/asynctask-threading-regression-confirmed.html
        task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[]) null);

        return task;
    }

    public AsyncTask executeApiAsync(Intent data, OpenPgpDataSource dataSource, IOpenPgpSinkResultCallback<Void> callback) {
        OpenPgpSourceSinkAsyncTask<Void> task = new OpenPgpSourceSinkAsyncTask<>(data, dataSource, null, callback);

        // don't serialize async tasks!
        // http://commonsware.com/blog/2012/04/20/asynctask-threading-regression-confirmed.html
        task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[]) null);

        return task;
    }

    public void executeApiAsync(Intent data, InputStream is, OutputStream os, IOpenPgpCallback callback) {
        OpenPgpAsyncTask task = new OpenPgpAsyncTask(data, is, os, callback);

        // don't serialize async tasks!
        // http://commonsware.com/blog/2012/04/20/asynctask-threading-regression-confirmed.html
        task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[]) null);
    }

    public static class OpenPgpDataResult<T> {
        Intent apiResult;
        T sinkResult;

        public OpenPgpDataResult(Intent apiResult, T sinkResult) {
            this.apiResult = apiResult;
            this.sinkResult = sinkResult;
        }
    }

    public <T> OpenPgpDataResult<T> executeApi(Intent data, OpenPgpDataSource dataSource, OpenPgpDataSink<T> dataSink) {
        ParcelFileDescriptor input = null;
        ParcelFileDescriptor output = null;
        try {
            if (dataSource != null) {
                Long expectedSize = dataSource.getSizeForProgress();
                if (expectedSize != null) {
                    data.putExtra(EXTRA_DATA_LENGTH, (long) expectedSize);
                } else {
                    data.removeExtra(EXTRA_PROGRESS_MESSENGER);
                }
                input = dataSource.startPumpThread();
            }

            DataSinkTransferThread<T> pumpThread = null;
            int outputPipeId = 0;

            if (dataSink != null) {
                outputPipeId = mPipeIdGen.incrementAndGet();
                output = mService.createOutputPipe(outputPipeId);
                pumpThread = ParcelFileDescriptorUtil.asyncPipeToDataSink(dataSink, output);
            }

            Intent result = executeApi(data, input, outputPipeId);

            if (pumpThread == null) {
                return new OpenPgpDataResult<>(result, null);
            }

            // wait for ALL data being pumped from remote side
            pumpThread.join();
            return new OpenPgpDataResult<>(result, pumpThread.getResult());
        } catch (Exception e) {
            Log.e(OpenPgpApi.TAG, "Exception in executeApi call", e);
            Intent result = new Intent();
            result.putExtra(RESULT_CODE, RESULT_CODE_ERROR);
            result.putExtra(RESULT_ERROR,
                    new OpenPgpError(OpenPgpError.CLIENT_SIDE_ERROR, e.getMessage()));
            return new OpenPgpDataResult<>(result, null);
        } finally {
            closeLoudly(output);
        }
    }

    public Intent executeApi(Intent data, InputStream is, OutputStream os) {
        ParcelFileDescriptor input = null;
        ParcelFileDescriptor output = null;
        try {
            if (is != null) {
                input = ParcelFileDescriptorUtil.pipeFrom(is);
            }

            Thread pumpThread = null;
            int outputPipeId = 0;

            if (os != null) {
                outputPipeId = mPipeIdGen.incrementAndGet();
                output = mService.createOutputPipe(outputPipeId);
                pumpThread = ParcelFileDescriptorUtil.pipeTo(os, output);
            }

            Intent result = executeApi(data, input, outputPipeId);

            // wait for ALL data being pumped from remote side
            if (pumpThread != null) {
                pumpThread.join();
            }

            return result;
        } catch (Exception e) {
            Log.e(OpenPgpApi.TAG, "Exception in executeApi call", e);
            Intent result = new Intent();
            result.putExtra(RESULT_CODE, RESULT_CODE_ERROR);
            result.putExtra(RESULT_ERROR,
                    new OpenPgpError(OpenPgpError.CLIENT_SIDE_ERROR, e.getMessage()));
            return result;
        } finally {
            closeLoudly(output);
        }
    }

    public static abstract class OpenPgpDataSource {
        private boolean isCancelled;
        private ParcelFileDescriptor writeSidePfd;


        public abstract void writeTo(OutputStream os) throws IOException;

        public Long getSizeForProgress() {
            return null;
        }

        public boolean isCancelled() {
            return isCancelled;
        }

        public ParcelFileDescriptor startPumpThread() throws IOException {
            if (writeSidePfd != null) {
                throw new IllegalStateException("startPumpThread() must only be called once!");
            }
            ParcelFileDescriptor[] pipe = ParcelFileDescriptor.createPipe();
            ParcelFileDescriptor readSidePfd = pipe[0];
            writeSidePfd = pipe[1];

            new DataSourceTransferThread(this, new ParcelFileDescriptor.AutoCloseOutputStream(writeSidePfd)).start();

            return readSidePfd;
        }

        private void cancel() {
            isCancelled = true;
            try {
                writeSidePfd.close();
            } catch (IOException e) {
                // this is fine
            }
        }
    }

    public interface OpenPgpDataSink<T> {
        T processData(InputStream is) throws IOException;
    }

    public Intent executeApi(Intent data, OpenPgpDataSource dataSource, OutputStream os) {
        ParcelFileDescriptor input = null;
        ParcelFileDescriptor output;
        try {
            if (dataSource != null) {
                Long expectedSize = dataSource.getSizeForProgress();
                if (expectedSize != null) {
                    data.putExtra(EXTRA_DATA_LENGTH, (long) expectedSize);
                } else {
                    data.removeExtra(EXTRA_PROGRESS_MESSENGER);
                }
                input = dataSource.startPumpThread();
            }

            Thread pumpThread = null;
            int outputPipeId = 0;

            if (os != null) {
                outputPipeId = mPipeIdGen.incrementAndGet();
                output = mService.createOutputPipe(outputPipeId);
                pumpThread = ParcelFileDescriptorUtil.pipeTo(os, output);
            }

            Intent result = executeApi(data, input, outputPipeId);

            // wait for ALL data being pumped from remote side
            if (pumpThread != null) {
                pumpThread.join();
            }

            return result;
        } catch (Exception e) {
            Log.e(OpenPgpApi.TAG, "Exception in executeApi call", e);
            Intent result = new Intent();
            result.putExtra(RESULT_CODE, RESULT_CODE_ERROR);
            result.putExtra(RESULT_ERROR,
                    new OpenPgpError(OpenPgpError.CLIENT_SIDE_ERROR, e.getMessage()));
            return result;
        }
    }

    /**
     * InputStream and OutputStreams are always closed after operating on them!
     */
    private Intent executeApi(Intent data, ParcelFileDescriptor input, int outputPipeId) {
        try {
            // always send version from client
            data.putExtra(EXTRA_API_VERSION, OpenPgpApi.API_VERSION);

            Intent result;

            // blocks until result is ready
            result = mService.execute(data, input, outputPipeId);

            // set class loader to current context to allow unparcelling
            // of OpenPgpError and OpenPgpSignatureResult
            // http://stackoverflow.com/a/3806769
            result.setExtrasClassLoader(mContext.getClassLoader());

            return result;
        } catch (Exception e) {
            Log.e(OpenPgpApi.TAG, "Exception in executeApi call", e);
            Intent result = new Intent();
            result.putExtra(RESULT_CODE, RESULT_CODE_ERROR);
            result.putExtra(RESULT_ERROR,
                    new OpenPgpError(OpenPgpError.CLIENT_SIDE_ERROR, e.getMessage()));
            return result;
        } finally {
            // close() is required to halt the TransferThread
            closeLoudly(input);
        }
    }

    private static void closeLoudly(ParcelFileDescriptor input) {
        if (input != null) {
            try {
                input.close();
            } catch (IOException e) {
                Log.e(OpenPgpApi.TAG, "IOException when closing ParcelFileDescriptor!", e);
            }
        }
    }

    public interface PermissionPingCallback {
        void onPgpPermissionCheckResult(Intent result);
    }

    public void checkPermissionPing(final PermissionPingCallback permissionPingCallback) {
        Intent intent = new Intent(OpenPgpApi.ACTION_CHECK_PERMISSION);
        executeApiAsync(intent, null, null, new IOpenPgpCallback() {
            @Override
            public void onReturn(Intent result) {
                permissionPingCallback.onPgpPermissionCheckResult(result);
            }
        });
    }
}