src/main/java/org/apache/commons/codec/binary/BaseNCodecOutputStream.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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
 *
 *      https://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.codec.binary;

import static org.apache.commons.codec.binary.BaseNCodec.EOF;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Objects;

import org.apache.commons.codec.binary.BaseNCodec.Context;
import org.apache.commons.codec.binary.BaseNCodecOutputStream.AbstractBuilder;

/**
 * Abstract superclass for Base-N output streams.
 * <p>
 * To write the EOF marker without closing the stream, call {@link #eof()} or use an <a href="https://commons.apache.org/proper/commons-io/">Apache Commons
 * IO</a>
 * <a href= "https://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/output/CloseShieldOutputStream.html" >CloseShieldOutputStream</a>.
 * </p>
 *
 * @param <C> A BaseNCodec subclass.
 * @param <T> A BaseNCodecInputStream subclass.
 * @param <B> A subclass.
 * @see Base16OutputStream
 * @see Base32OutputStream
 * @see Base64OutputStream
 * @since 1.5
 */
public class BaseNCodecOutputStream<C extends BaseNCodec, T extends BaseNCodecOutputStream<C, T, B>, B extends AbstractBuilder<T, C, B>>
        extends FilterOutputStream {

    /**
     * Builds output stream instances in {@link BaseNCodec} format.
     *
     * @param <T> The output stream type to build.
     * @param <C> A {@link BaseNCodec} subclass.
     * @param <B> The builder subclass.
     * @since 1.20.0
     */
    public abstract static class AbstractBuilder<T, C extends BaseNCodec, B extends AbstractBuilder<T, C, B>>
        extends AbstractBaseNCodecStreamBuilder<T, C, B> {

        private OutputStream outputStream;

        /**
         * Constructs a new instance.
         */
        public AbstractBuilder() {
            // super
        }

        /**
         * Gets the input stream.
         *
         * @return The input stream.
         */
        protected OutputStream getOutputStream() {
            return outputStream;
        }

        /**
         * Sets the input stream.
         *
         * @param outputStream The input stream.
         * @return {@code this} instance.
         */
        public B setOutputStream(final OutputStream outputStream) {
            this.outputStream = outputStream;
            return asThis();
        }
    }

    private final boolean doEncode;
    private final C baseNCodec;
    private final byte[] singleByte = new byte[1];
    private final Context context = new Context();

    /**
     * Constructs a new instance.
     *
     * @param builder A builder.
     * @since 1.20.0
     */
    @SuppressWarnings("resource") // Caller closes.
    protected BaseNCodecOutputStream(final AbstractBuilder<T, C, B> builder) {
        super(builder.getOutputStream());
        this.baseNCodec = builder.getBaseNCodec();
        this.doEncode = builder.getEncode();
    }

    /**
     * Constructs a new instance.
     *
     * TODO should this be protected?
     *
     * @param outputStream The underlying output or null.
     * @param basedCodec   A BaseNCodec.
     * @param doEncode     true to encode, false to decode, TODO should be an enum?.
     */
    public BaseNCodecOutputStream(final OutputStream outputStream, final C basedCodec, final boolean doEncode) {
        super(outputStream);
        this.baseNCodec = basedCodec;
        this.doEncode = doEncode;
    }

    /**
     * Closes this output stream and releases any system resources associated with the stream.
     * <p>
     * To write the EOF marker without closing the stream, call {@link #eof()} or use an <a href="https://commons.apache.org/proper/commons-io/">Apache Commons
     * IO</a>
     * <a href= "https://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/output/CloseShieldOutputStream.html" >CloseShieldOutputStream</a>.
     * </p>
     *
     * @throws IOException Thrown if an I/O error occurs.
     */
    @Override
    public void close() throws IOException {
        eof();
        flush();
        out.close();
    }

    /**
     * Writes EOF.
     *
     * @since 1.11
     */
    public void eof() {
        // Notify encoder of EOF (-1).
        if (doEncode) {
            baseNCodec.encode(singleByte, 0, EOF, context);
        } else {
            baseNCodec.decode(singleByte, 0, EOF, context);
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream.
     *
     * @throws IOException Thrown if an I/O error occurs.
     */
    @Override
    public void flush() throws IOException {
        flush(true);
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream. If propagate is true, the wrapped stream will also be
     * flushed.
     *
     * @param propagate boolean flag to indicate whether the wrapped OutputStream should also be flushed.
     * @throws IOException Thrown if an I/O error occurs.
     */
    private void flush(final boolean propagate) throws IOException {
        final int avail = baseNCodec.available(context);
        if (avail > 0) {
            final byte[] buf = new byte[avail];
            final int c = baseNCodec.readResults(buf, 0, avail, context);
            if (c > 0) {
                out.write(buf, 0, c);
            }
        }
        if (propagate) {
            out.flush();
        }
    }

    /**
     * Returns true if decoding behavior is strict. Decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid encoding.
     *
     * <p>
     * The default is false for lenient encoding. Decoding will compose trailing bits into 8-bit bytes and discard the remainder.
     * </p>
     *
     * @return true if using strict decoding.
     * @since 1.15
     */
    public boolean isStrictDecoding() {
        return baseNCodec.isStrictDecoding();
    }

    /**
     * Writes {@code len} bytes from the specified {@code b} array starting at {@code offset} to this output stream.
     *
     * @param array  source byte array.
     * @param offset where to start reading the bytes.
     * @param len    maximum number of bytes to write.
     * @throws IOException               if an I/O error occurs.
     * @throws NullPointerException      if the byte array parameter is null.
     * @throws IndexOutOfBoundsException if offset, len or buffer size are invalid.
     */
    @Override
    public void write(final byte[] array, final int offset, final int len) throws IOException {
        Objects.requireNonNull(array, "array");
        if (offset < 0 || len < 0 || offset > array.length || offset + len > array.length) {
            throw new IndexOutOfBoundsException();
        }
        if (len > 0) {
            if (doEncode) {
                baseNCodec.encode(array, offset, len, context);
            } else {
                baseNCodec.decode(array, offset, len, context);
            }
            flush(false);
        }
    }

    /**
     * Writes the specified {@code byte} to this output stream.
     *
     * @param i source byte.
     * @throws IOException Thrown if an I/O error occurs.
     */
    @Override
    public void write(final int i) throws IOException {
        singleByte[0] = (byte) i;
        write(singleByte, 0, 1);
    }
}