ReaderInputStream

/*
 * 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.io.input;

import static org.apache.commons.io.IOUtils.EOF;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CodingErrorAction;
import java.util.Objects;

import org.apache.commons.io.Charsets;
import org.apache.commons.io.IOUtils;
import org.apache.commons.io.build.AbstractStreamBuilder;
import org.apache.commons.io.charset.CharsetEncoders;

/**
 * {@link InputStream} implementation that reads a character stream from a {@link Reader} and transforms it to a byte stream using a specified charset encoding.
 * The stream is transformed using a {@link CharsetEncoder} object, guaranteeing that all charset encodings supported by the JRE are handled correctly. In
 * particular for charsets such as UTF-16, the implementation ensures that one and only one byte order marker is produced.
 * <p>
 * Since in general it is not possible to predict the number of characters to be read from the {@link Reader} to satisfy a read request on the
 * {@link ReaderInputStream}, all reads from the {@link Reader} are buffered. There is therefore no well defined correlation between the current position of the
 * {@link Reader} and that of the {@link ReaderInputStream}. This also implies that in general there is no need to wrap the underlying {@link Reader} in a
 * {@link BufferedReader}.
 * </p>
 * <p>
 * {@link ReaderInputStream} implements the inverse transformation of {@link InputStreamReader}; in the following example, reading from {@code in2}
 * would return the same byte sequence as reading from {@code in} (provided that the initial byte sequence is legal with respect to the charset encoding):
 * </p>
 * <p>
 * To build an instance, use {@link Builder}.
 * </p>
 * <pre>
 * InputStream inputStream = ...
 * Charset cs = ...
 * InputStreamReader reader = new InputStreamReader(inputStream, cs);
 * ReaderInputStream in2 = ReaderInputStream.builder()
 *   .setReader(reader)
 *   .setCharset(cs)
 *   .get();
 * </pre>
 * <p>
 * {@link ReaderInputStream} implements the same transformation as {@link OutputStreamWriter}, except that the control flow is reversed: both classes
 * transform a character stream into a byte stream, but {@link OutputStreamWriter} pushes data to the underlying stream, while {@link ReaderInputStream}
 * pulls it from the underlying stream.
 * </p>
 * <p>
 * Note that while there are use cases where there is no alternative to using this class, very often the need to use this class is an indication of a flaw in
 * the design of the code. This class is typically used in situations where an existing API only accepts an {@link InputStream}, but where the most natural way
 * to produce the data is as a character stream, by providing a {@link Reader} instance. An example of a situation where this problem may appear is when
 * implementing the {@code javax.activation.DataSource} interface from the Java Activation Framework.
 * </p>
 * <p>
 * The {@link #available()} method of this class always returns 0. The methods {@link #mark(int)} and {@link #reset()} are not supported.
 * </p>
 * <p>
 * Instances of {@link ReaderInputStream} are not thread safe.
 * </p>
 *
 * @see Builder
 * @see org.apache.commons.io.output.WriterOutputStream
 * @since 2.0
 */
public class ReaderInputStream extends AbstractInputStream {

    // @formatter:off
    /**
     * Builds a new {@link ReaderInputStream}.
     *
     * <p>
     * For example:
     * </p>
     * <pre>{@code
     * ReaderInputStream s = ReaderInputStream.builder()
     *   .setPath(path)
     *   .setCharsetEncoder(Charset.defaultCharset().newEncoder())
     *   .get();}
     * </pre>
     *
     * @see #get()
     * @since 2.12.0
     */
    // @formatter:on
    public static class Builder extends AbstractStreamBuilder<ReaderInputStream, Builder> {

        private CharsetEncoder charsetEncoder = newEncoder(getCharset());

        /**
         * Constructs a new builder of {@link ReaderInputStream}.
         */
        public Builder() {
            // empty
        }

        /**
         * Builds a new {@link ReaderInputStream}.
         *
         * <p>
         * You must set an aspect that supports {@link #getReader()}, otherwise, this method throws an exception.
         * </p>
         * <p>
         * This builder uses the following aspects:
         * </p>
         * <ul>
         * <li>{@link #getReader()} gets the target aspect.</li>
         * <li>{@link #getBufferSize()}</li>
         * <li>{@link #getCharset()}</li>
         * <li>{@link CharsetEncoder}</li>
         * </ul>
         *
         * @return a new instance.
         * @throws UnsupportedOperationException if the origin cannot provide a {@link Reader}.
         * @throws IllegalStateException         if the {@code origin} is {@code null}.
         * @throws IOException                   if an I/O error occurs converting to a {@link Reader} using {@link #getReader()}.
         * @see #getReader()
         * @see CharsetEncoder
         * @see #getBufferSize()
         * @see #getUnchecked()
         */
        @Override
        public ReaderInputStream get() throws IOException {
            return new ReaderInputStream(this);
        }

        CharsetEncoder getCharsetEncoder() {
            return charsetEncoder;
        }

        @Override
        public Builder setCharset(final Charset charset) {
            super.setCharset(charset);
            charsetEncoder = newEncoder(getCharset());
            return this;
        }

        /**
         * Sets the charset encoder. Assumes that the caller has configured the encoder.
         *
         * @param newEncoder the charset encoder, null resets to a default encoder.
         * @return {@code this} instance.
         */
        public Builder setCharsetEncoder(final CharsetEncoder newEncoder) {
            charsetEncoder = CharsetEncoders.toCharsetEncoder(newEncoder, () -> newEncoder(getCharsetDefault()));
            super.setCharset(charsetEncoder.charset());
            return this;
        }

    }

    /**
     * Constructs a new {@link Builder}.
     *
     * @return a new {@link Builder}.
     * @since 2.12.0
     */
    public static Builder builder() {
        return new Builder();
    }

    static int checkMinBufferSize(final CharsetEncoder charsetEncoder, final int bufferSize) {
        final float minRequired = minBufferSize(charsetEncoder);
        if (bufferSize < minRequired) {
            throw new IllegalArgumentException(String.format("Buffer size %,d must be at least %s for a CharsetEncoder %s.", bufferSize, minRequired,
                    charsetEncoder.charset().displayName()));
        }
        return bufferSize;
    }

    static float minBufferSize(final CharsetEncoder charsetEncoder) {
        return charsetEncoder.maxBytesPerChar() * 2;
    }

    private static CharsetEncoder newEncoder(final Charset charset) {
        // @formatter:off
        return Charsets.toCharset(charset).newEncoder()
                .onMalformedInput(CodingErrorAction.REPLACE)
                .onUnmappableCharacter(CodingErrorAction.REPLACE);
        // @formatter:on
    }

    private final Reader reader;

    private final CharsetEncoder charsetEncoder;

    /**
     * CharBuffer used as input for the decoder. It should be reasonably large as we read data from the underlying Reader into this buffer.
     */
    private final CharBuffer encoderIn;
    /**
     * ByteBuffer used as output for the decoder. This buffer can be small as it is only used to transfer data from the decoder to the buffer provided by the
     * caller.
     */
    private final ByteBuffer encoderOut;

    private CoderResult lastCoderResult;

    private boolean endOfInput;

    @SuppressWarnings("resource") // caller closes.
    private ReaderInputStream(final Builder builder) throws IOException {
        this(builder.getReader(), builder.charsetEncoder, builder.getBufferSize());
    }

    /**
     * Constructs a new {@link ReaderInputStream} that uses the virtual machine's {@link Charset#defaultCharset() default charset} with a default input buffer
     * size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
     *
     * @param reader the target {@link Reader}
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader) {
        this(reader, Charset.defaultCharset());
    }

    /**
     * Constructs a new {@link ReaderInputStream} with a default input buffer size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
     *
     * <p>
     * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
     * </p>
     *
     * @param reader  the target {@link Reader}
     * @param charset the charset encoding
     * @deprecated Use {@link ReaderInputStream#builder()} instead, will be protected for subclasses.
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final Charset charset) {
        this(reader, charset, IOUtils.DEFAULT_BUFFER_SIZE);
    }

    /**
     * Constructs a new {@link ReaderInputStream}.
     *
     * <p>
     * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
     * </p>
     *
     * @param reader     the target {@link Reader}.
     * @param charset    the charset encoding.
     * @param bufferSize the size of the input buffer in number of characters.
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final Charset charset, final int bufferSize) {
        // @formatter:off
        this(reader,
            Charsets.toCharset(charset).newEncoder()
                    .onMalformedInput(CodingErrorAction.REPLACE)
                    .onUnmappableCharacter(CodingErrorAction.REPLACE),
             bufferSize);
        // @formatter:on
    }

    /**
     * Constructs a new {@link ReaderInputStream}.
     *
     * <p>
     * This constructor does not call {@link CharsetEncoder#reset() reset} on the provided encoder. The caller of this constructor should do this when providing
     * an encoder which had already been in use.
     * </p>
     *
     * @param reader         the target {@link Reader}
     * @param charsetEncoder the charset encoder
     * @since 2.1
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final CharsetEncoder charsetEncoder) {
        this(reader, charsetEncoder, IOUtils.DEFAULT_BUFFER_SIZE);
    }

    /**
     * Constructs a new {@link ReaderInputStream}.
     *
     * <p>
     * This constructor does not call {@link CharsetEncoder#reset() reset} on the provided encoder. The caller of this constructor should do this when providing
     * an encoder which had already been in use.
     * </p>
     *
     * @param reader         the target {@link Reader}
     * @param charsetEncoder the charset encoder, null defaults to the default Charset encoder.
     * @param bufferSize     the size of the input buffer in number of characters
     * @since 2.1
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final CharsetEncoder charsetEncoder, final int bufferSize) {
        this.reader = reader;
        this.charsetEncoder = CharsetEncoders.toCharsetEncoder(charsetEncoder);
        this.encoderIn = CharBuffer.allocate(checkMinBufferSize(this.charsetEncoder, bufferSize));
        this.encoderIn.flip();
        this.encoderOut = ByteBuffer.allocate(128);
        this.encoderOut.flip();
    }

    /**
     * Constructs a new {@link ReaderInputStream} with a default input buffer size of {@value IOUtils#DEFAULT_BUFFER_SIZE} characters.
     *
     * <p>
     * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
     * </p>
     *
     * @param reader      the target {@link Reader}
     * @param charsetName the name of the charset encoding
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final String charsetName) {
        this(reader, charsetName, IOUtils.DEFAULT_BUFFER_SIZE);
    }

    /**
     * Constructs a new {@link ReaderInputStream}.
     *
     * <p>
     * The encoder created for the specified charset will use {@link CodingErrorAction#REPLACE} for malformed input and unmappable characters.
     * </p>
     *
     * @param reader      the target {@link Reader}
     * @param charsetName the name of the charset encoding, null maps to the default Charset.
     * @param bufferSize  the size of the input buffer in number of characters
     * @deprecated Use {@link ReaderInputStream#builder()} instead
     */
    @Deprecated
    public ReaderInputStream(final Reader reader, final String charsetName, final int bufferSize) {
        this(reader, Charsets.toCharset(charsetName), bufferSize);
    }

    @Override
    public int available() throws IOException {
        if (encoderOut.hasRemaining()) {
            return encoderOut.remaining();
        }
        return 0;
    }

    /**
     * Closes the stream. This method will cause the underlying {@link Reader} to be closed.
     *
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void close() throws IOException {
        reader.close();
        super.close();
    }

    /**
     * Fills the internal char buffer from the reader.
     *
     * @throws IOException If an I/O error occurs
     */
    private void fillBuffer() throws IOException {
        if (endOfInput) {
            return;
        }
        if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
            encoderIn.compact();
            final int position = encoderIn.position();
            // We don't use Reader#read(CharBuffer) here because it is more efficient
            // to write directly to the underlying char array (the default implementation
            // copies data to a temporary char array).
            final int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
            if (c == EOF) {
                endOfInput = true;
            } else {
                encoderIn.position(position + c);
            }
            encoderIn.flip();
        }
        encoderOut.compact();
        lastCoderResult = charsetEncoder.encode(encoderIn, encoderOut, endOfInput);
        if (endOfInput) {
            lastCoderResult = charsetEncoder.flush(encoderOut);
        }
        if (lastCoderResult.isError()) {
            lastCoderResult.throwException();
        }
        encoderOut.flip();
    }

    /**
     * Gets the CharsetEncoder.
     *
     * @return the CharsetEncoder.
     */
    CharsetEncoder getCharsetEncoder() {
        return charsetEncoder;
    }

    /**
     * Reads a single byte.
     *
     * @return either the byte read or {@code -1} if the end of the stream has been reached
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read() throws IOException {
        checkOpen();
        for (;;) {
            if (encoderOut.hasRemaining()) {
                return encoderOut.get() & 0xFF;
            }
            fillBuffer();
            if (endOfInput && !encoderOut.hasRemaining()) {
                return EOF;
            }
        }
    }

    /**
     * Reads the specified number of bytes into an array.
     *
     * @param b the byte array to read into
     * @return the number of bytes read or {@code -1} if the end of the stream has been reached
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read(final byte[] b) throws IOException {
        return read(b, 0, b.length);
    }

    /**
     * Reads the specified number of bytes into an array.
     *
     * @param array the byte array to read into
     * @param off   the offset to start reading bytes into
     * @param len   the number of bytes to read
     * @return the number of bytes read or {@code -1} if the end of the stream has been reached
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read(final byte[] array, int off, int len) throws IOException {
        Objects.requireNonNull(array, "array");
        if (len < 0 || off < 0 || off + len > array.length) {
            throw new IndexOutOfBoundsException("Array size=" + array.length + ", offset=" + off + ", length=" + len);
        }
        int read = 0;
        if (len == 0) {
            return 0; // Always return 0 if len == 0
        }
        while (len > 0) {
            if (encoderOut.hasRemaining()) { // Data from the last read not fully copied
                final int c = Math.min(encoderOut.remaining(), len);
                encoderOut.get(array, off, c);
                off += c;
                len -= c;
                read += c;
            } else if (endOfInput) { // Already reach EOF in the last read
                break;
            } else { // Read again
                fillBuffer();
            }
        }
        return read == 0 && endOfInput ? EOF : read;
    }
}