engine/shell/platform/android/io/flutter/view/ResourceExtractor.java

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.view;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.res.AssetManager;
import android.os.AsyncTask;
import android.os.Build;
import android.util.Log;
import io.flutter.util.PathUtils;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.*;
import java.util.Collection;
import java.util.HashSet;
import java.util.Scanner;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.zip.CRC32;
import java.util.zip.ZipEntry;
import java.util.zip.ZipException;
import java.util.zip.ZipFile;

/**
 * A class to initialize the native code.
 **/
class ResourceExtractor {
    private static final String TAG = "ResourceExtractor";
    private static final String TIMESTAMP_PREFIX = "res_timestamp-";

    private static final int BUFFER_SIZE = 16 * 1024;

    @SuppressWarnings("deprecation")
    static long getVersionCode(PackageInfo packageInfo) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
            return packageInfo.getLongVersionCode();
        } else {
            return packageInfo.versionCode;
        }
    }

    private class ExtractTask extends AsyncTask<Void, Void, Void> {
        ExtractTask() { }

        @Override
        protected Void doInBackground(Void... unused) {
            final File dataDir = new File(PathUtils.getDataDirectory(mContext));

            JSONObject updateManifest = readUpdateManifest();
            if (!validateUpdateManifest(updateManifest)) {
                updateManifest = null;
            }

            final String timestamp = checkTimestamp(dataDir, updateManifest);
            if (timestamp == null) {
                return null;
            }

            deleteFiles();

            if (updateManifest != null) {
                if (!extractUpdate(dataDir)) {
                    return null;
                }
            }

            if (!extractAPK(dataDir)) {
                return null;
            }

            if (timestamp != null) {
                try {
                    new File(dataDir, timestamp).createNewFile();
                } catch (IOException e) {
                    Log.w(TAG, "Failed to write resource timestamp");
                }
            }

            return null;
        }
    }

    private final Context mContext;
    private final HashSet<String> mResources;
    private ExtractTask mExtractTask;

    ResourceExtractor(Context context) {
        mContext = context;
        mResources = new HashSet<>();
    }

    ResourceExtractor addResource(String resource) {
        mResources.add(resource);
        return this;
    }

    ResourceExtractor addResources(Collection<String> resources) {
        mResources.addAll(resources);
        return this;
    }

    ResourceExtractor start() {
        assert mExtractTask == null;
        mExtractTask = new ExtractTask();
        mExtractTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        return this;
    }

    void waitForCompletion() {
        if (mExtractTask == null) {
            return;
        }

        try {
            mExtractTask.get();
        } catch (CancellationException | ExecutionException | InterruptedException e) {
            deleteFiles();
        }
    }

    private String[] getExistingTimestamps(File dataDir) {
        return dataDir.list(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
                return name.startsWith(TIMESTAMP_PREFIX);
            }
        });
    }

    private void deleteFiles() {
        final File dataDir = new File(PathUtils.getDataDirectory(mContext));
        for (String resource : mResources) {
            final File file = new File(dataDir, resource);
            if (file.exists()) {
                file.delete();
            }
        }
        final String[] existingTimestamps = getExistingTimestamps(dataDir);
        if (existingTimestamps == null) {
            return;
        }
        for (String timestamp : existingTimestamps) {
            new File(dataDir, timestamp).delete();
        }
    }

    /// Returns true if successfully unpacked APK resources,
    /// otherwise deletes all resources and returns false.
    private boolean extractAPK(File dataDir) {
        final AssetManager manager = mContext.getResources().getAssets();

        byte[] buffer = null;
        for (String asset : mResources) {
            try {
                final File output = new File(dataDir, asset);
                if (output.exists()) {
                    continue;
                }
                if (output.getParentFile() != null) {
                    output.getParentFile().mkdirs();
                }

                try (InputStream is = manager.open(asset);
                     OutputStream os = new FileOutputStream(output)) {
                    if (buffer == null) {
                        buffer = new byte[BUFFER_SIZE];
                    }

                    int count = 0;
                    while ((count = is.read(buffer, 0, BUFFER_SIZE)) != -1) {
                        os.write(buffer, 0, count);
                    }

                    os.flush();
                    Log.i(TAG, "Extracted baseline resource " + asset);
                }

            } catch (FileNotFoundException fnfe) {
                continue;

            } catch (IOException ioe) {
                Log.w(TAG, "Exception unpacking resources: " + ioe.getMessage());
                deleteFiles();
                return false;
            }
        }

        return true;
    }

    /// Returns true if successfully unpacked update resources or if there is no update,
    /// otherwise deletes all resources and returns false.
    private boolean extractUpdate(File dataDir) {
        ResourceUpdater resourceUpdater = FlutterMain.getResourceUpdater();
        if (resourceUpdater == null) {
            return true;
        }

        File updateFile = resourceUpdater.getPatch();
        if (!updateFile.exists()) {
            return true;
        }

        ZipFile zipFile;
        try {
            zipFile = new ZipFile(updateFile);

        } catch (IOException e) {
            Log.w(TAG, "Exception unpacking resources: " + e.getMessage());
            deleteFiles();
            return false;
        }

        byte[] buffer = null;
        for (String asset : mResources) {
            ZipEntry entry = zipFile.getEntry(asset);
            if (entry == null) {
                continue;
            }

            final File output = new File(dataDir, asset);
            if (output.exists()) {
                continue;
            }
            if (output.getParentFile() != null) {
                output.getParentFile().mkdirs();
            }

            try (InputStream is = zipFile.getInputStream(entry);
                 OutputStream os = new FileOutputStream(output)) {
                if (buffer == null) {
                    buffer = new byte[BUFFER_SIZE];
                }

                int count = 0;
                while ((count = is.read(buffer, 0, BUFFER_SIZE)) != -1) {
                    os.write(buffer, 0, count);
                }

                os.flush();
                Log.i(TAG, "Extracted override resource " + asset);

            } catch (FileNotFoundException fnfe) {
                continue;

            } catch (IOException ioe) {
                Log.w(TAG, "Exception unpacking resources: " + ioe.getMessage());
                deleteFiles();
                return false;
            }
        }

        return true;
    }

    // Returns null if extracted resources are found and match the current APK version
    // and update version if any, otherwise returns the current APK and update version.
    private String checkTimestamp(File dataDir, JSONObject updateManifest) {

        PackageManager packageManager = mContext.getPackageManager();
        PackageInfo packageInfo = null;

        try {
            packageInfo = packageManager.getPackageInfo(mContext.getPackageName(), 0);
        } catch (PackageManager.NameNotFoundException e) {
            return TIMESTAMP_PREFIX;
        }

        if (packageInfo == null) {
            return TIMESTAMP_PREFIX;
        }

        String expectedTimestamp =
                TIMESTAMP_PREFIX + getVersionCode(packageInfo) + "-" + packageInfo.lastUpdateTime;

        if (updateManifest != null) {
            String buildNumber = updateManifest.optString("buildNumber", null);
            if (buildNumber == null) {
                Log.w(TAG, "Invalid update manifest: buildNumber");
            } else {
                String patchNumber = updateManifest.optString("patchNumber", null);
                if (!buildNumber.equals(Long.toString(getVersionCode(packageInfo)))) {
                    Log.w(TAG, "Outdated update file for " + getVersionCode(packageInfo));
                } else {
                    ResourceUpdater resourceUpdater = FlutterMain.getResourceUpdater();
                    assert resourceUpdater != null;
                    File patchFile = resourceUpdater.getPatch();
                    assert patchFile.exists();
                    if (patchNumber != null) {
                        expectedTimestamp += "-" + patchNumber + "-" + patchFile.lastModified();
                    } else {
                        expectedTimestamp += "-" + patchFile.lastModified();
                    }
                }
            }
        }

        final String[] existingTimestamps = getExistingTimestamps(dataDir);

        if (existingTimestamps == null) {
            Log.i(TAG, "No extracted resources found");
            return expectedTimestamp;
        }

        if (existingTimestamps.length == 1) {
            Log.i(TAG, "Found extracted resources " + existingTimestamps[0]);
        }

        if (existingTimestamps.length != 1
                || !expectedTimestamp.equals(existingTimestamps[0])) {
            Log.i(TAG, "Resource version mismatch " + expectedTimestamp);
            return expectedTimestamp;
        }

        return null;
    }

    /// Returns true if the downloaded update file was indeed built for this APK.
    private boolean validateUpdateManifest(JSONObject updateManifest) {
        if (updateManifest == null) {
            return false;
        }

        String baselineChecksum = updateManifest.optString("baselineChecksum", null);
        if (baselineChecksum == null) {
            Log.w(TAG, "Invalid update manifest: baselineChecksum");
            return false;
        }

        final AssetManager manager = mContext.getResources().getAssets();
        try (InputStream is = manager.open("flutter_assets/isolate_snapshot_data")) {
            CRC32 checksum = new CRC32();

            int count = 0;
            byte[] buffer = new byte[BUFFER_SIZE];
            while ((count = is.read(buffer, 0, BUFFER_SIZE)) != -1) {
                checksum.update(buffer, 0, count);
            }

            if (!baselineChecksum.equals(String.valueOf(checksum.getValue()))) {
                Log.w(TAG, "Mismatched update file for APK");
                return false;
            }

            return true;

        } catch (IOException e) {
            Log.w(TAG, "Could not read APK: " + e);
            return false;
        }
    }

    /// Returns null if no update manifest is found.
    private JSONObject readUpdateManifest() {
        ResourceUpdater resourceUpdater = FlutterMain.getResourceUpdater();
        if (resourceUpdater == null) {
            return null;
        }

        File updateFile = resourceUpdater.getPatch();
        if (!updateFile.exists()) {
            return null;
        }

        try {
            ZipFile zipFile = new ZipFile(updateFile);
            ZipEntry entry = zipFile.getEntry("manifest.json");
            if (entry == null) {
                Log.w(TAG, "Invalid update file: " + updateFile);
                return null;
            }

            // Read and parse the entire JSON file as single operation.
            Scanner scanner = new Scanner(zipFile.getInputStream(entry));
            return new JSONObject(scanner.useDelimiter("\\A").next());

        } catch (IOException | JSONException e) {
            Log.w(TAG, "Invalid update file: " + e);
            return null;

        }
    }
}