1 /* 2 * Copyright 2022 Google LLC 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package com.google.android.libraries.mobiledatadownload.file.backends; 17 18 import android.net.Uri; 19 import android.os.ParcelFileDescriptor; 20 import android.util.Pair; 21 import com.google.android.libraries.mobiledatadownload.file.common.MalformedUriException; 22 import java.io.Closeable; 23 24 /** 25 * Helper class for "fd:" URIs that refer to file descriptors. The opaque part of these URIs is 26 * simply the file descriptor int value stringified. These URIs are transient and should never be 27 * stored. 28 * 29 * <p>The primary use case is fetching a ParcelFileDescriptor from Java and passing that down to 30 * native code. The URI is paired with a closer which must be called to free system resources. Java 31 * can do so immediately after passing the URI to native; if the native fd backend needs to keep the 32 * file descriptor for longer, it will make a duplicate. 33 * 34 * <p>TODO: Java implementation of file descriptor backend. 35 */ 36 public final class FileDescriptorUri { 37 38 /** Create a pair of URI and closer for underlying resources from a ParcelFileDescriptor. */ fromParcelFileDescriptor(ParcelFileDescriptor pfd)39 public static Pair<Uri, Closeable> fromParcelFileDescriptor(ParcelFileDescriptor pfd) { 40 int fd = pfd.getFd(); 41 Uri uri = new Uri.Builder().scheme("fd").opaquePart(String.valueOf(fd)).build(); 42 // NOTE: ParcelFileDescriptor doesn't implement Closeable on SDK 15, so we need to wrap 43 return Pair.create(uri, () -> pfd.close()); 44 } 45 46 /** Gets the integer file descriptor from this URI. */ getFd(Uri uri)47 public static int getFd(Uri uri) throws MalformedUriException { 48 if (!uri.getScheme().equals("fd")) { 49 throw new MalformedUriException("Scheme must be 'fd'"); 50 } 51 try { 52 return Integer.parseInt(uri.getSchemeSpecificPart()); 53 } catch (NumberFormatException e) { 54 throw new MalformedUriException(e); 55 } 56 } 57 FileDescriptorUri()58 private FileDescriptorUri() {} 59 } 60