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/*
* Copyright 2022 Google LLC
*
* 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 com.google.android.libraries.mobiledatadownload.file.openers;
import com.google.android.libraries.mobiledatadownload.file.OpenContext;
import com.google.android.libraries.mobiledatadownload.file.Opener;
import com.google.protobuf.ExtensionRegistryLite;
import com.google.protobuf.MessageLite;
import com.google.protobuf.Parser;
import java.io.IOException;
import java.io.InputStream;
/**
* Opener for reading Protocol Buffers from file. It is based on the Java Proto Lite implementation;
* see <internal> for more information. Note that this opener reads the entire stream into a single
* message, meaning that delimited files are not supported. If the byte contents of the Uri cannot
* be parsed as a valid protocol message, throws {@link InvalidProtocolBufferException}.
*
* <p>Usage: <code>
* MyProto proto = storage.open(uri, ReadProtoOpener.create(MyProto.parser()));
* </code>
*
* <p>TODO(b/75909287): consider adding alternative implementation for multi-proto files
*/
public final class ReadProtoOpener<T extends MessageLite> implements Opener<T> {
private final Parser<T> parser;
private ExtensionRegistryLite registry = ExtensionRegistryLite.getEmptyRegistry();
private ReadProtoOpener(Parser<T> parser) {
this.parser = parser;
}
/** Creates a new opener instance that reads protos using the given {@code parser}. */
public static <T extends MessageLite> ReadProtoOpener<T> create(Parser<T> parser) {
return new ReadProtoOpener<T>(parser);
}
/**
* Creates a new opener instance that reads protos using the parser of the given {@code message}.
* This can be useful if the type of T is unavailable at compile time (i.e. it's a generic).
*/
public static <T extends MessageLite> ReadProtoOpener<T> create(T message) {
@SuppressWarnings("unchecked") // safe cast because getParserForType API must return a Parser<T>
Parser<T> parser = (Parser<T>) message.getParserForType();
return new ReadProtoOpener<T>(parser);
}
/** Adds an extension registry used while parsing the proto. */
public ReadProtoOpener<T> withExtensionRegistry(ExtensionRegistryLite registry) {
this.registry = registry;
return this;
}
@Override
public T open(OpenContext openContext) throws IOException {
try (InputStream in = ReadStreamOpener.create().open(openContext)) {
return parser.parseFrom(in, registry);
}
}
}
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