sebbASF commented on code in PR #497: URL: https://github.com/apache/commons-io/pull/497#discussion_r1368468564
########## src/main/java/org/apache/commons/io/input/TrailerInputStream.java: ########## @@ -0,0 +1,193 @@ +/* + * 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 org.apache.commons.io.input; + +import java.io.IOException; +import java.io.InputStream; +import org.apache.commons.io.IOUtils; + +/** + * Reads the underlying input stream while holding back the trailer. + * + * <p> + * "Normal" read calls read the underlying stream except the last few bytes (the trailer). The + * trailer is updated with each read call. The trailer can be gotten by one of the copyTrailer + * overloads. + * </p> + * + * <p> + * It is safe to fetch the trailer at any time but the trailer will change with each read call + * until the underlying stream is EOF. + * </p> + * + * <p> + * Useful, e.g., for handling checksums: payload is followed by a fixed size hash, so while + * streaming the payload the trailer finally contains the expected hash (this example needs + * extra caution to revert actions when the final checksum match fails). + * </p> + * + * <p> + * No mark/reset support. + * </p> + * + * <p> + * Not thread-safe. If accessed by multiple threads concurrently, external synchronization is + * necessary. + * </p> + */ +public final class TrailerInputStream extends InputStream { + + // Extending FilterInputStream or ProxyInputStream would save overriding + // * close, and + // * available + // but would require to override + // * mark, + // * reset, and + // * markSupported. + // So, there is no benefit in extending FilterInputStream or ProxyInputStream over InputStream + // as mark/reset is not supported by this implementation. + + // The current implementation is incompatible with mark/reset as it doesn't track which bytes are + // already read and which ones are new. This tracking would be necessary to not overwrite the + // trailer with earlier bytes in the source stream. Remember that the trailer is not meant to + // contain the last read bytes but the last bytes in the stream (which differs when using reset + // to jump to an earlier position of the source stream). + + private final InputStream source; + /** + * Invariant: After every method call which exited without exception, the trailer has to be + * completely filled. + */ + private final byte[] trailer; + + /** + * Constructs the TrailerInputStream and initializes the trailer buffer. + * + * <p> + * Reads exactly {@code trailerLength} bytes from {@code source}. + * </p> + * + * @param source underlying stream from which is read. + * @param trailerLength the length of the trailer which is hold back (must be >= 0). + * @throws IOException initializing the trailer buffer failed. + */ + public TrailerInputStream(final InputStream source, final int trailerLength) + throws IOException { + if (trailerLength < 0) { Review Comment: I don't see the point of allowing a zero-length trailer Also, it probably make sense to have an upper limit. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@commons.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
