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.openers; 17 18 import com.google.android.libraries.mobiledatadownload.file.OpenContext; 19 import com.google.android.libraries.mobiledatadownload.file.Opener; 20 import com.google.errorprone.annotations.CanIgnoreReturnValue; 21 import com.google.protobuf.ExtensionRegistryLite; 22 import com.google.protobuf.MessageLite; 23 import com.google.protobuf.Parser; 24 import java.io.IOException; 25 import java.io.InputStream; 26 27 /** 28 * Opener for reading Protocol Buffers from file. It is based on the Java Proto Lite implementation; 29 * see <internal> for more information. Note that this opener reads the entire stream into a single 30 * message, meaning that delimited files are not supported. If the byte contents of the Uri cannot 31 * be parsed as a valid protocol message, throws {@link InvalidProtocolBufferException}. 32 * 33 * <p>Usage: <code> 34 * MyProto proto = storage.open(uri, ReadProtoOpener.create(MyProto.parser())); 35 * </code> 36 * 37 * <p>TODO(b/75909287): consider adding alternative implementation for multi-proto files 38 */ 39 public final class ReadProtoOpener<T extends MessageLite> implements Opener<T> { 40 41 private final Parser<T> parser; 42 private ExtensionRegistryLite registry = ExtensionRegistryLite.getEmptyRegistry(); 43 ReadProtoOpener(Parser<T> parser)44 private ReadProtoOpener(Parser<T> parser) { 45 this.parser = parser; 46 } 47 48 /** Creates a new opener instance that reads protos using the given {@code parser}. */ create(Parser<T> parser)49 public static <T extends MessageLite> ReadProtoOpener<T> create(Parser<T> parser) { 50 return new ReadProtoOpener<T>(parser); 51 } 52 53 /** 54 * Creates a new opener instance that reads protos using the parser of the given {@code message}. 55 * This can be useful if the type of T is unavailable at compile time (i.e. it's a generic). 56 */ create(T message)57 public static <T extends MessageLite> ReadProtoOpener<T> create(T message) { 58 @SuppressWarnings("unchecked") // safe cast because getParserForType API must return a Parser<T> 59 Parser<T> parser = (Parser<T>) message.getParserForType(); 60 return new ReadProtoOpener<T>(parser); 61 } 62 63 /** Adds an extension registry used while parsing the proto. */ 64 @CanIgnoreReturnValue withExtensionRegistry(ExtensionRegistryLite registry)65 public ReadProtoOpener<T> withExtensionRegistry(ExtensionRegistryLite registry) { 66 this.registry = registry; 67 return this; 68 } 69 70 @Override open(OpenContext openContext)71 public T open(OpenContext openContext) throws IOException { 72 try (InputStream in = ReadStreamOpener.create().open(openContext)) { 73 return parser.parseFrom(in, registry); 74 } 75 } 76 } 77