android/provider/FontsContract.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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 android.provider;

import android.annotation.IntDef;
import android.annotation.IntRange;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.ProviderInfo;
import android.content.pm.Signature;
import android.database.Cursor;
import android.graphics.Typeface;
import android.graphics.fonts.Font;
import android.graphics.fonts.FontFamily;
import android.graphics.fonts.FontStyle;
import android.graphics.fonts.FontVariationAxis;
import android.net.Uri;
import android.os.CancellationSignal;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.ParcelFileDescriptor;
import android.os.Process;
import android.util.Log;
import android.util.LruCache;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.annotations.VisibleForTesting;
import com.android.internal.util.Preconditions;

import java.io.FileInputStream;
import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Utility class to deal with Font ContentProviders.
 */
public class FontsContract {
    private static final String TAG = "FontsContract";

    /**
     * Defines the constants used in a response from a Font Provider. The cursor returned from the
     * query should have the ID column populated with the content uri ID for the resulting font.
     * This should point to a real file or shared memory, as the client will mmap the given file
     * descriptor. Pipes, sockets and other non-mmap-able file descriptors will fail to load in the
     * client application.
     */
    public static final class Columns implements BaseColumns {

        // Do not instantiate.
        private Columns() {}

        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * may populate this column with a long for the font file ID. The client will request a file
         * descriptor to "file/FILE_ID" with this ID immediately under the top-level content URI. If
         * not present, the client will request a file descriptor to the top-level URI with the
         * given base font ID. Note that several results may return the same file ID, e.g. for TTC
         * files with different indices.
         */
        public static final String FILE_ID = "file_id";
        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * should have this column populated with an int for the ttc index for the resulting font.
         */
        public static final String TTC_INDEX = "font_ttc_index";
        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * may populate this column with the font variation settings String information for the
         * font.
         */
        public static final String VARIATION_SETTINGS = "font_variation_settings";
        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * should have this column populated with the int weight for the resulting font. This value
         * should be between 100 and 900. The most common values are 400 for regular weight and 700
         * for bold weight.
         */
        public static final String WEIGHT = "font_weight";
        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * should have this column populated with the int italic for the resulting font. This should
         * be 0 for regular style and 1 for italic.
         */
        public static final String ITALIC = "font_italic";
        /**
         * Constant used to request data from a font provider. The cursor returned from the query
         * should have this column populated to indicate the result status of the
         * query. This will be checked before any other data in the cursor. Possible values are
         * {@link #RESULT_CODE_OK}, {@link #RESULT_CODE_FONT_NOT_FOUND},
         * {@link #RESULT_CODE_MALFORMED_QUERY} and {@link #RESULT_CODE_FONT_UNAVAILABLE} for system
         * defined values. You may also define your own values in the 0x000010000..0xFFFF0000 range.
         * If not present, {@link #RESULT_CODE_OK} will be assumed.
         */
        public static final String RESULT_CODE = "result_code";

        /**
         * Constant used to represent a result was retrieved successfully. The given fonts will be
         * attempted to retrieve immediately via
         * {@link android.content.ContentProvider#openFile(Uri, String)}. See {@link #RESULT_CODE}.
         */
        public static final int RESULT_CODE_OK = 0;
        /**
         * Constant used to represent a result was not found. See {@link #RESULT_CODE}.
         */
        public static final int RESULT_CODE_FONT_NOT_FOUND = 1;
        /**
         * Constant used to represent a result was found, but cannot be provided at this moment. Use
         * this to indicate, for example, that a font needs to be fetched from the network. See
         * {@link #RESULT_CODE}.
         */
        public static final int RESULT_CODE_FONT_UNAVAILABLE = 2;
        /**
         * Constant used to represent that the query was not in a supported format by the provider.
         * See {@link #RESULT_CODE}.
         */
        public static final int RESULT_CODE_MALFORMED_QUERY = 3;
    }

    private static final Object sLock = new Object();
    @GuardedBy("sLock")
    private static Handler sHandler;
    @GuardedBy("sLock")
    private static HandlerThread sThread;
    @GuardedBy("sLock")
    private static Set<String> sInQueueSet;

    private volatile static Context sContext;  // set once in setApplicationContextForResources

    private static final LruCache<String, Typeface> sTypefaceCache = new LruCache<>(16);

    private FontsContract() {
    }

    /** @hide */
    public static void setApplicationContextForResources(Context context) {
        sContext = context.getApplicationContext();
    }

    /**
     * Object represent a font entry in the family returned from {@link #fetchFonts}.
     */
    public static class FontInfo {
        private final Uri mUri;
        private final int mTtcIndex;
        private final FontVariationAxis[] mAxes;
        private final int mWeight;
        private final boolean mItalic;
        private final int mResultCode;

        /**
         * Creates a Font with all the information needed about a provided font.
         * @param uri A URI associated to the font file.
         * @param ttcIndex If providing a TTC_INDEX file, the index to point to. Otherwise, 0.
         * @param axes If providing a variation font, the settings for it. May be null.
         * @param weight An integer that indicates the font weight.
         * @param italic A boolean that indicates the font is italic style or not.
         * @param resultCode A boolean that indicates the font contents is ready.
         */
        /** @hide */
        public FontInfo(@NonNull Uri uri, @IntRange(from = 0) int ttcIndex,
                @Nullable FontVariationAxis[] axes, @IntRange(from = 1, to = 1000) int weight,
                boolean italic, int resultCode) {
            mUri = Preconditions.checkNotNull(uri);
            mTtcIndex = ttcIndex;
            mAxes = axes;
            mWeight = weight;
            mItalic = italic;
            mResultCode = resultCode;
        }

        /**
         * Returns a URI associated to this record.
         */
        public @NonNull Uri getUri() {
            return mUri;
        }

        /**
         * Returns the index to be used to access this font when accessing a TTC file.
         */
        public @IntRange(from = 0) int getTtcIndex() {
            return mTtcIndex;
        }

        /**
         * Returns the list of axes associated to this font.
         */
        public @Nullable FontVariationAxis[] getAxes() {
            return mAxes;
        }

        /**
         * Returns the weight value for this font.
         */
        public @IntRange(from = 1, to = 1000) int getWeight() {
            return mWeight;
        }

        /**
         * Returns whether this font is italic.
         */
        public boolean isItalic() {
            return mItalic;
        }

        /**
         * Returns result code.
         *
         * {@link FontsContract.Columns#RESULT_CODE}
         */
        public int getResultCode() {
            return mResultCode;
        }
    }

    /**
     * Object returned from {@link #fetchFonts}.
     */
    public static class FontFamilyResult {
        /**
         * Constant represents that the font was successfully retrieved. Note that when this value
         * is set and {@link #getFonts} returns an empty array, it means there were no fonts
         * matching the given query.
         */
        public static final int STATUS_OK = 0;

        /**
         * Constant represents that the given certificate was not matched with the provider's
         * signature. {@link #getFonts} returns null if this status was set.
         */
        public static final int STATUS_WRONG_CERTIFICATES = 1;

        /**
         * Constant represents that the provider returns unexpected data. {@link #getFonts} returns
         * null if this status was set. For example, this value is set when the font provider
         * gives invalid format of variation settings.
         */
        public static final int STATUS_UNEXPECTED_DATA_PROVIDED = 2;

        /**
         * Constant represents that the fetching font data was rejected by system. This happens if
         * the passed context is restricted.
         */
        public static final int STATUS_REJECTED = 3;

        /** @hide */
        @IntDef(prefix = { "STATUS_" }, value = {
                STATUS_OK,
                STATUS_WRONG_CERTIFICATES,
                STATUS_UNEXPECTED_DATA_PROVIDED
        })
        @Retention(RetentionPolicy.SOURCE)
        @interface FontResultStatus {}

        private final @FontResultStatus int mStatusCode;
        private final FontInfo[] mFonts;

        /** @hide */
        public FontFamilyResult(@FontResultStatus int statusCode, @Nullable FontInfo[] fonts) {
            mStatusCode = statusCode;
            mFonts = fonts;
        }

        public @FontResultStatus int getStatusCode() {
            return mStatusCode;
        }

        public @NonNull FontInfo[] getFonts() {
            return mFonts;
        }
    }

    private static final int THREAD_RENEWAL_THRESHOLD_MS = 10000;

    private static final long SYNC_FONT_FETCH_TIMEOUT_MS = 500;

    // We use a background thread to post the content resolving work for all requests on. This
    // thread should be quit/stopped after all requests are done.
    // TODO: Factor out to other class. Consider to switch MessageQueue.IdleHandler.
    private static final Runnable sReplaceDispatcherThreadRunnable = new Runnable() {
        @Override
        public void run() {
            synchronized (sLock) {
                if (sThread != null) {
                    sThread.quitSafely();
                    sThread = null;
                    sHandler = null;
                }
            }
        }
    };

    /** @hide */
    public static Typeface getFontSync(FontRequest request) {
        final String id = request.getIdentifier();
        Typeface cachedTypeface = sTypefaceCache.get(id);
        if (cachedTypeface != null) {
            return cachedTypeface;
        }

        synchronized (sLock) {
            // It is possible that Font is loaded during the thread sleep time
            // re-check the cache to avoid re-loading the font
            cachedTypeface = sTypefaceCache.get(id);
            if (cachedTypeface != null) {
                return cachedTypeface;
            }

            // Unfortunately the typeface is not available at this time, but requesting from
            // the font provider takes too much time. For now, request the font data to ensure
            // it is in the cache next time and return.
            if (sHandler == null) {
                sThread = new HandlerThread("fonts", Process.THREAD_PRIORITY_BACKGROUND);
                sThread.start();
                sHandler = new Handler(sThread.getLooper());
            }
            final Lock lock = new ReentrantLock();
            final Condition cond = lock.newCondition();
            final AtomicReference<Typeface> holder = new AtomicReference<>();
            final AtomicBoolean waiting = new AtomicBoolean(true);
            final AtomicBoolean timeout = new AtomicBoolean(false);

            sHandler.post(() -> {
                try {
                    FontFamilyResult result = fetchFonts(sContext, null, request);
                    if (result.getStatusCode() == FontFamilyResult.STATUS_OK) {
                        Typeface typeface = buildTypeface(sContext, null, result.getFonts());
                        if (typeface != null) {
                            sTypefaceCache.put(id, typeface);
                        }
                        holder.set(typeface);
                    }
                } catch (NameNotFoundException e) {
                    // Ignore.
                }
                lock.lock();
                try {
                    if (!timeout.get()) {
                      waiting.set(false);
                      cond.signal();
                    }
                } finally {
                    lock.unlock();
                }
            });
            sHandler.removeCallbacks(sReplaceDispatcherThreadRunnable);
            sHandler.postDelayed(sReplaceDispatcherThreadRunnable, THREAD_RENEWAL_THRESHOLD_MS);

            long remaining = TimeUnit.MILLISECONDS.toNanos(SYNC_FONT_FETCH_TIMEOUT_MS);
            lock.lock();
            try {
                if (!waiting.get()) {
                    return holder.get();
                }
                for (;;) {
                    try {
                        remaining = cond.awaitNanos(remaining);
                    } catch (InterruptedException e) {
                        // do nothing.
                    }
                    if (!waiting.get()) {
                        return holder.get();
                    }
                    if (remaining <= 0) {
                        timeout.set(true);
                        Log.w(TAG, "Remote font fetch timed out: " +
                                request.getProviderAuthority() + "/" + request.getQuery());
                        return null;
                    }
                }
            } finally {
                lock.unlock();
            }
        }
    }

    /**
     * Interface used to receive asynchronously fetched typefaces.
     */
    public static class FontRequestCallback {
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the given
         * provider was not found on the device.
         */
        public static final int FAIL_REASON_PROVIDER_NOT_FOUND = -1;
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the given
         * provider must be authenticated and the given certificates do not match its signature.
         */
        public static final int FAIL_REASON_WRONG_CERTIFICATES = -2;
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the font
         * returned by the provider was not loaded properly.
         */
        public static final int FAIL_REASON_FONT_LOAD_ERROR = -3;
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the font
         * provider did not return any results for the given query.
         */
        public static final int FAIL_REASON_FONT_NOT_FOUND = Columns.RESULT_CODE_FONT_NOT_FOUND;
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the font
         * provider found the queried font, but it is currently unavailable.
         */
        public static final int FAIL_REASON_FONT_UNAVAILABLE = Columns.RESULT_CODE_FONT_UNAVAILABLE;
        /**
         * Constant returned by {@link #onTypefaceRequestFailed(int)} signaling that the given
         * query was not supported by the provider.
         */
        public static final int FAIL_REASON_MALFORMED_QUERY = Columns.RESULT_CODE_MALFORMED_QUERY;

        /** @hide */
        @IntDef(prefix = { "FAIL_" }, value = {
                FAIL_REASON_PROVIDER_NOT_FOUND,
                FAIL_REASON_FONT_LOAD_ERROR,
                FAIL_REASON_FONT_NOT_FOUND,
                FAIL_REASON_FONT_UNAVAILABLE,
                FAIL_REASON_MALFORMED_QUERY
        })
        @Retention(RetentionPolicy.SOURCE)
        @interface FontRequestFailReason {}

        public FontRequestCallback() {}

        /**
         * Called then a Typeface request done via {@link #requestFonts} is complete. Note that this
         * method will not be called if {@link #onTypefaceRequestFailed(int)} is called instead.
         * @param typeface  The Typeface object retrieved.
         */
        public void onTypefaceRetrieved(Typeface typeface) {}

        /**
         * Called when a Typeface request done via {@link #requestFonts}} fails.
         * @param reason One of {@link #FAIL_REASON_PROVIDER_NOT_FOUND},
         *               {@link #FAIL_REASON_FONT_NOT_FOUND},
         *               {@link #FAIL_REASON_FONT_LOAD_ERROR},
         *               {@link #FAIL_REASON_FONT_UNAVAILABLE} or
         *               {@link #FAIL_REASON_MALFORMED_QUERY} if returned by the system. May also be
         *               a positive value greater than 0 defined by the font provider as an
         *               additional error code. Refer to the provider's documentation for more
         *               information on possible returned error codes.
         */
        public void onTypefaceRequestFailed(@FontRequestFailReason int reason) {}
    }

    /**
     * Create a typeface object given a font request. The font will be asynchronously fetched,
     * therefore the result is delivered to the given callback. See {@link FontRequest}.
     * Only one of the methods in callback will be invoked, depending on whether the request
     * succeeds or fails. These calls will happen on the caller thread.
     *
     * Note that the result Typeface may be cached internally and the same instance will be returned
     * the next time you call this method with the same request. If you want to bypass this cache,
     * use {@link #fetchFonts} and {@link #buildTypeface} instead.
     *
     * @param context A context to be used for fetching from font provider.
     * @param request A {@link FontRequest} object that identifies the provider and query for the
     *                request. May not be null.
     * @param handler A handler to be processed the font fetching.
     * @param cancellationSignal A signal to cancel the operation in progress, or null if none. If
     *                           the operation is canceled, then {@link
     *                           android.os.OperationCanceledException} will be thrown.
     * @param callback A callback that will be triggered when results are obtained. May not be null.
     */
    public static void requestFonts(@NonNull Context context, @NonNull FontRequest request,
            @NonNull Handler handler, @Nullable CancellationSignal cancellationSignal,
            @NonNull FontRequestCallback callback) {

        final Handler callerThreadHandler = new Handler();
        final Typeface cachedTypeface = sTypefaceCache.get(request.getIdentifier());
        if (cachedTypeface != null) {
            callerThreadHandler.post(() -> callback.onTypefaceRetrieved(cachedTypeface));
            return;
        }

        handler.post(() -> {
            FontFamilyResult result;
            try {
                result = fetchFonts(context, cancellationSignal, request);
            } catch (NameNotFoundException e) {
                callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                        FontRequestCallback.FAIL_REASON_PROVIDER_NOT_FOUND));
                return;
            }

            // Same request might be dispatched during fetchFonts. Check the cache again.
            final Typeface anotherCachedTypeface = sTypefaceCache.get(request.getIdentifier());
            if (anotherCachedTypeface != null) {
                callerThreadHandler.post(() -> callback.onTypefaceRetrieved(anotherCachedTypeface));
                return;
            }

            if (result.getStatusCode() != FontFamilyResult.STATUS_OK) {
                switch (result.getStatusCode()) {
                    case FontFamilyResult.STATUS_WRONG_CERTIFICATES:
                        callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                                FontRequestCallback.FAIL_REASON_WRONG_CERTIFICATES));
                        return;
                    case FontFamilyResult.STATUS_UNEXPECTED_DATA_PROVIDED:
                        callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                                FontRequestCallback.FAIL_REASON_FONT_LOAD_ERROR));
                        return;
                    default:
                        // fetchFont returns unexpected status type. Fallback to load error.
                        callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                                FontRequestCallback.FAIL_REASON_FONT_LOAD_ERROR));
                        return;
                }
            }

            final FontInfo[] fonts = result.getFonts();
            if (fonts == null || fonts.length == 0) {
                callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                        FontRequestCallback.FAIL_REASON_FONT_NOT_FOUND));
                return;
            }
            for (final FontInfo font : fonts) {
                if (font.getResultCode() != Columns.RESULT_CODE_OK) {
                    // We proceed if all font entry is ready to use. Otherwise report the first
                    // error.
                    final int resultCode = font.getResultCode();
                    if (resultCode < 0) {
                        // Negative values are reserved for internal errors. Fallback to load error.
                        callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                                FontRequestCallback.FAIL_REASON_FONT_LOAD_ERROR));
                    } else {
                        callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                                resultCode));
                    }
                    return;
                }
            }

            final Typeface typeface = buildTypeface(context, cancellationSignal, fonts);
            if (typeface == null) {
                // Something went wrong during reading font files. This happens if the given font
                // file is an unsupported font type.
                callerThreadHandler.post(() -> callback.onTypefaceRequestFailed(
                        FontRequestCallback.FAIL_REASON_FONT_LOAD_ERROR));
                return;
            }

            sTypefaceCache.put(request.getIdentifier(), typeface);
            callerThreadHandler.post(() -> callback.onTypefaceRetrieved(typeface));
        });
    }

    /**
     * Fetch fonts given a font request.
     *
     * @param context A {@link Context} to be used for fetching fonts.
     * @param cancellationSignal A signal to cancel the operation in progress, or null if none. If
     *                           the operation is canceled, then {@link
     *                           android.os.OperationCanceledException} will be thrown when the
     *                           query is executed.
     * @param request A {@link FontRequest} object that identifies the provider and query for the
     *                request.
     *
     * @return {@link FontFamilyResult}
     *
     * @throws NameNotFoundException If requested package or authority was not found in system.
     */
    public static @NonNull FontFamilyResult fetchFonts(
            @NonNull Context context, @Nullable CancellationSignal cancellationSignal,
            @NonNull FontRequest request) throws NameNotFoundException {
        if (context.isRestricted()) {
            // TODO: Should we allow if the peer process is system or myself?
            return new FontFamilyResult(FontFamilyResult.STATUS_REJECTED, null);
        }
        ProviderInfo providerInfo = getProvider(context.getPackageManager(), request);
        if (providerInfo == null) {
            return new FontFamilyResult(FontFamilyResult.STATUS_WRONG_CERTIFICATES, null);

        }
        try {
            FontInfo[] fonts = getFontFromProvider(
                    context, request, providerInfo.authority, cancellationSignal);
            return new FontFamilyResult(FontFamilyResult.STATUS_OK, fonts);
        } catch (IllegalArgumentException e) {
            return new FontFamilyResult(FontFamilyResult.STATUS_UNEXPECTED_DATA_PROVIDED, null);
        }
    }

    /**
     * Build a Typeface from an array of {@link FontInfo}
     *
     * Results that are marked as not ready will be skipped.
     *
     * @param context A {@link Context} that will be used to fetch the font contents.
     * @param cancellationSignal A signal to cancel the operation in progress, or null if none. If
     *                           the operation is canceled, then {@link
     *                           android.os.OperationCanceledException} will be thrown.
     * @param fonts An array of {@link FontInfo} to be used to create a Typeface.
     * @return A Typeface object. Returns null if typeface creation fails.
     */
    public static Typeface buildTypeface(@NonNull Context context,
            @Nullable CancellationSignal cancellationSignal, @NonNull FontInfo[] fonts) {
        if (context.isRestricted()) {
            // TODO: Should we allow if the peer process is system or myself?
            return null;
        }
        final Map<Uri, ByteBuffer> uriBuffer =
                prepareFontData(context, fonts, cancellationSignal);
        if (uriBuffer.isEmpty()) {
            return null;
        }

        FontFamily.Builder familyBuilder = null;
        for (FontInfo fontInfo : fonts) {
            final ByteBuffer buffer = uriBuffer.get(fontInfo.getUri());
            if (buffer == null) {
                continue;
            }
            try {
                final Font font = new Font.Builder(buffer)
                        .setWeight(fontInfo.getWeight())
                        .setSlant(fontInfo.isItalic()
                                ? FontStyle.FONT_SLANT_ITALIC : FontStyle.FONT_SLANT_UPRIGHT)
                        .setTtcIndex(fontInfo.getTtcIndex())
                        .setFontVariationSettings(fontInfo.getAxes())
                        .build();
                if (familyBuilder == null) {
                    familyBuilder = new FontFamily.Builder(font);
                } else {
                    familyBuilder.addFont(font);
                }
            } catch (IllegalArgumentException e) {
                // To be a compatible behavior with API28 or before, catch IllegalArgumentExcetpion
                // thrown by native code and returns null.
                return null;
            } catch (IOException e) {
                continue;
            }
        }
        if (familyBuilder == null) {
            return null;
        }

        final FontFamily family = familyBuilder.build();

        final FontStyle normal = new FontStyle(FontStyle.FONT_WEIGHT_NORMAL,
                FontStyle.FONT_SLANT_UPRIGHT);
        Font bestFont = family.getFont(0);
        int bestScore = normal.getMatchScore(bestFont.getStyle());
        for (int i = 1; i < family.getSize(); ++i) {
            final Font candidate = family.getFont(i);
            final int score = normal.getMatchScore(candidate.getStyle());
            if (score < bestScore) {
                bestFont = candidate;
                bestScore = score;
            }
        }
        return new Typeface.CustomFallbackBuilder(family).setStyle(bestFont.getStyle()).build();
    }

    /**
     * A helper function to create a mapping from {@link Uri} to {@link ByteBuffer}.
     *
     * Skip if the file contents is not ready to be read.
     *
     * @param context A {@link Context} to be used for resolving content URI in
     *                {@link FontInfo}.
     * @param fonts An array of {@link FontInfo}.
     * @return A map from {@link Uri} to {@link ByteBuffer}.
     */
    private static Map<Uri, ByteBuffer> prepareFontData(Context context, FontInfo[] fonts,
            CancellationSignal cancellationSignal) {
        final HashMap<Uri, ByteBuffer> out = new HashMap<>();
        final ContentResolver resolver = context.getContentResolver();

        for (FontInfo font : fonts) {
            if (font.getResultCode() != Columns.RESULT_CODE_OK) {
                continue;
            }

            final Uri uri = font.getUri();
            if (out.containsKey(uri)) {
                continue;
            }

            ByteBuffer buffer = null;
            try (final ParcelFileDescriptor pfd =
                    resolver.openFileDescriptor(uri, "r", cancellationSignal)) {
                if (pfd != null) {
                    try (final FileInputStream fis =
                            new FileInputStream(pfd.getFileDescriptor())) {
                        final FileChannel fileChannel = fis.getChannel();
                        final long size = fileChannel.size();
                        buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, size);
                    } catch (IOException e) {
                        // ignore
                    }
                }
            } catch (IOException e) {
                // ignore
            }

            // TODO: try other approach?, e.g. read all contents instead of mmap.

            out.put(uri, buffer);
        }
        return Collections.unmodifiableMap(out);
    }

    /** @hide */
    @VisibleForTesting
    public static @Nullable ProviderInfo getProvider(
            PackageManager packageManager, FontRequest request) throws NameNotFoundException {
        String providerAuthority = request.getProviderAuthority();
        ProviderInfo info = packageManager.resolveContentProvider(providerAuthority, 0);
        if (info == null) {
            throw new NameNotFoundException("No package found for authority: " + providerAuthority);
        }

        if (!info.packageName.equals(request.getProviderPackage())) {
            throw new NameNotFoundException("Found content provider " + providerAuthority
                    + ", but package was not " + request.getProviderPackage());
        }
        // Trust system apps without signature checks
        if (info.applicationInfo.isSystemApp()) {
            return info;
        }

        List<byte[]> signatures;
        PackageInfo packageInfo = packageManager.getPackageInfo(info.packageName,
                PackageManager.GET_SIGNATURES);
        signatures = convertToByteArrayList(packageInfo.signatures);
        Collections.sort(signatures, sByteArrayComparator);

        List<List<byte[]>> requestCertificatesList = request.getCertificates();
        for (int i = 0; i < requestCertificatesList.size(); ++i) {
            // Make a copy so we can sort it without modifying the incoming data.
            List<byte[]> requestSignatures = new ArrayList<>(requestCertificatesList.get(i));
            Collections.sort(requestSignatures, sByteArrayComparator);
            if (equalsByteArrayList(signatures, requestSignatures)) {
                return info;
            }
        }
        return null;
    }

    private static final Comparator<byte[]> sByteArrayComparator = (l, r) -> {
        if (l.length != r.length) {
            return l.length - r.length;
        }
        for (int i = 0; i < l.length; ++i) {
            if (l[i] != r[i]) {
                return l[i] - r[i];
            }
        }
        return 0;
    };

    private static boolean equalsByteArrayList(
            List<byte[]> signatures, List<byte[]> requestSignatures) {
        if (signatures.size() != requestSignatures.size()) {
            return false;
        }
        for (int i = 0; i < signatures.size(); ++i) {
            if (!Arrays.equals(signatures.get(i), requestSignatures.get(i))) {
                return false;
            }
        }
        return true;
    }

    private static List<byte[]> convertToByteArrayList(Signature[] signatures) {
        List<byte[]> shas = new ArrayList<>();
        for (int i = 0; i < signatures.length; ++i) {
            shas.add(signatures[i].toByteArray());
        }
        return shas;
    }

    /** @hide */
    @VisibleForTesting
    public static @NonNull FontInfo[] getFontFromProvider(
            Context context, FontRequest request, String authority,
            CancellationSignal cancellationSignal) {
        ArrayList<FontInfo> result = new ArrayList<>();
        final Uri uri = new Uri.Builder().scheme(ContentResolver.SCHEME_CONTENT)
                .authority(authority)
                .build();
        final Uri fileBaseUri = new Uri.Builder().scheme(ContentResolver.SCHEME_CONTENT)
                .authority(authority)
                .appendPath("file")
                .build();
        try (Cursor cursor = context.getContentResolver().query(uri, new String[] { Columns._ID,
                        Columns.FILE_ID, Columns.TTC_INDEX, Columns.VARIATION_SETTINGS,
                        Columns.WEIGHT, Columns.ITALIC, Columns.RESULT_CODE },
                "query = ?", new String[] { request.getQuery() }, null, cancellationSignal);) {
            // TODO: Should we restrict the amount of fonts that can be returned?
            // TODO: Write documentation explaining that all results should be from the same family.
            if (cursor != null && cursor.getCount() > 0) {
                final int resultCodeColumnIndex = cursor.getColumnIndex(Columns.RESULT_CODE);
                result = new ArrayList<>();
                final int idColumnIndex = cursor.getColumnIndexOrThrow(Columns._ID);
                final int fileIdColumnIndex = cursor.getColumnIndex(Columns.FILE_ID);
                final int ttcIndexColumnIndex = cursor.getColumnIndex(Columns.TTC_INDEX);
                final int vsColumnIndex = cursor.getColumnIndex(Columns.VARIATION_SETTINGS);
                final int weightColumnIndex = cursor.getColumnIndex(Columns.WEIGHT);
                final int italicColumnIndex = cursor.getColumnIndex(Columns.ITALIC);
                while (cursor.moveToNext()) {
                    int resultCode = resultCodeColumnIndex != -1
                            ? cursor.getInt(resultCodeColumnIndex) : Columns.RESULT_CODE_OK;
                    final int ttcIndex = ttcIndexColumnIndex != -1
                            ? cursor.getInt(ttcIndexColumnIndex) : 0;
                    final String variationSettings = vsColumnIndex != -1
                            ? cursor.getString(vsColumnIndex) : null;

                    Uri fileUri;
                    if (fileIdColumnIndex == -1) {
                        long id = cursor.getLong(idColumnIndex);
                        fileUri = ContentUris.withAppendedId(uri, id);
                    } else {
                        long id = cursor.getLong(fileIdColumnIndex);
                        fileUri = ContentUris.withAppendedId(fileBaseUri, id);
                    }
                    int weight;
                    boolean italic;
                    if (weightColumnIndex != -1 && italicColumnIndex != -1) {
                        weight = cursor.getInt(weightColumnIndex);
                        italic = cursor.getInt(italicColumnIndex) == 1;
                    } else {
                        weight = Typeface.Builder.NORMAL_WEIGHT;
                        italic = false;
                    }
                    FontVariationAxis[] axes =
                            FontVariationAxis.fromFontVariationSettings(variationSettings);
                    result.add(new FontInfo(fileUri, ttcIndex, axes, weight, italic, resultCode));
                }
            }
        }
        return result.toArray(new FontInfo[0]);
    }
}