src/java.base/share/classes/sun/nio/cs/StreamDecoder.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 */

package sun.nio.cs;

import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.io.Reader;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CodingErrorAction;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.Arrays;

public class StreamDecoder extends Reader {

    private static final int MIN_BYTE_BUFFER_SIZE = 32;
    private static final int DEFAULT_BYTE_BUFFER_SIZE = 8192;

    private volatile boolean closed;

    private void ensureOpen() throws IOException {
        if (closed)
            throw new IOException("Stream closed");
    }

    // In order to handle surrogates properly we must never try to produce
    // fewer than two characters at a time.  If we're only asked to return one
    // character then the other is saved here to be returned later.
    //
    private boolean haveLeftoverChar = false;
    private char leftoverChar;


    // Factories for java.io.InputStreamReader

    public static StreamDecoder forInputStreamReader(InputStream in,
                                                     Object lock,
                                                     String charsetName)
        throws UnsupportedEncodingException
    {
        try {
            return new StreamDecoder(in, lock, Charset.forName(charsetName));
        } catch (IllegalCharsetNameException | UnsupportedCharsetException x) {
            throw new UnsupportedEncodingException (charsetName);
        }
    }

    public static StreamDecoder forInputStreamReader(InputStream in,
                                                     Object lock,
                                                     Charset cs)
    {
        return new StreamDecoder(in, lock, cs);
    }

    public static StreamDecoder forInputStreamReader(InputStream in,
                                                     Object lock,
                                                     CharsetDecoder dec)
    {
        return new StreamDecoder(in, lock, dec);
    }


    // Factory for java.nio.channels.Channels.newReader

    public static StreamDecoder forDecoder(ReadableByteChannel ch,
                                           CharsetDecoder dec,
                                           int minBufferCap)
    {
        return new StreamDecoder(ch, dec, minBufferCap);
    }


    // -- Public methods corresponding to those in InputStreamReader --

    // All synchronization and state/argument checking is done in these public
    // methods; the concrete stream-decoder subclasses defined below need not
    // do any such checking.

    public String getEncoding() {
        if (isOpen())
            return encodingName();
        return null;
    }

    public int read() throws IOException {
        return read0();
    }

    @SuppressWarnings("fallthrough")
    private int read0() throws IOException {
        synchronized (lock) {
            // Return the leftover char, if there is one
            if (haveLeftoverChar) {
                haveLeftoverChar = false;
                return leftoverChar;
            }

            // Convert more bytes
            char[] cb = new char[2];
            int n = read(cb, 0, 2);
            switch (n) {
            case -1:
                return -1;
            case 2:
                leftoverChar = cb[1];
                haveLeftoverChar = true;
                // FALL THROUGH
            case 1:
                return cb[0];
            default:
                assert false : n;
                return -1;
            }
        }
    }

    public int read(char[] cbuf, int offset, int length) throws IOException {
        synchronized (lock) {
            int off = offset;
            int len = length;

            ensureOpen();
            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
                ((off + len) > cbuf.length) || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            }
            if (len == 0)
                return 0;

            int n = 0;

            if (haveLeftoverChar) {
                // Copy the leftover char into the buffer
                cbuf[off] = leftoverChar;
                off++; len--;
                haveLeftoverChar = false;
                n = 1;
                if ((len == 0) || !implReady())
                    // Return now if this is all we can produce w/o blocking
                    return n;
            }

            if (len == 1) {
                // Treat single-character array reads just like read()
                int c = read0();
                if (c == -1)
                    return (n == 0) ? -1 : n;
                cbuf[off] = (char)c;
                return n + 1;
            }

            // Read remaining characters
            int nr = implRead(cbuf, off, off + len);

            // At this point, n is either 1 if a leftover character was read,
            // or 0 if no leftover character was read. If n is 1 and nr is -1,
            // indicating EOF, then we don't return their sum as this loses data.
            return (nr < 0) ? (n == 1 ? 1 : nr) : (n + nr);
        }
    }

    public boolean ready() throws IOException {
        synchronized (lock) {
            ensureOpen();
            return haveLeftoverChar || implReady();
        }
    }

    public void close() throws IOException {
        synchronized (lock) {
            if (closed)
                return;
            try {
                implClose();
            } finally {
                closed = true;
            }
        }
    }

    private boolean isOpen() {
        return !closed;
    }

    public void fillZeroToPosition() throws IOException {
        synchronized (lock) {
            Arrays.fill(bb.array(), bb.arrayOffset(),
                        bb.arrayOffset() + bb.position(), (byte)0);
        }
    }

    // -- Charset-based stream decoder impl --

    private final Charset cs;
    private final CharsetDecoder decoder;
    private final ByteBuffer bb;

    // Exactly one of these is non-null
    private final InputStream in;
    private final ReadableByteChannel ch;

    StreamDecoder(InputStream in, Object lock, Charset cs) {
        this(in, lock,
            cs.newDecoder()
                .onMalformedInput(CodingErrorAction.REPLACE)
                .onUnmappableCharacter(CodingErrorAction.REPLACE));
    }

    StreamDecoder(InputStream in, Object lock, CharsetDecoder dec) {
        super(lock);
        this.cs = dec.charset();
        this.decoder = dec;
        this.in = in;
        this.ch = null;
        this.bb = ByteBuffer.allocate(DEFAULT_BYTE_BUFFER_SIZE);
        bb.flip();                      // So that bb is initially empty
    }

    StreamDecoder(ReadableByteChannel ch, CharsetDecoder dec, int mbc) {
        this.in = null;
        this.ch = ch;
        this.decoder = dec;
        this.cs = dec.charset();
        this.bb = ByteBuffer.allocate(mbc < 0
                                  ? DEFAULT_BYTE_BUFFER_SIZE
                                  : (mbc < MIN_BYTE_BUFFER_SIZE
                                     ? MIN_BYTE_BUFFER_SIZE
                                     : mbc));
        bb.flip();
    }

    private int readBytes() throws IOException {
        bb.compact();
        try {
            if (ch != null) {
                // Read from the channel
                int n = ch.read(bb);
                if (n < 0)
                    return n;
            } else {
                // Read from the input stream, and then update the buffer
                int lim = bb.limit();
                int pos = bb.position();
                assert (pos <= lim);
                int rem = (pos <= lim ? lim - pos : 0);
                int n = in.read(bb.array(), bb.arrayOffset() + pos, rem);
                if (n < 0)
                    return n;
                if (n == 0)
                    throw new IOException("Underlying input stream returned zero bytes");
                assert (n <= rem) : "n = " + n + ", rem = " + rem;
                bb.position(pos + n);
            }
        } finally {
            // Flip even when an IOException is thrown,
            // otherwise the stream will stutter
            bb.flip();
        }

        int rem = bb.remaining();
        assert (rem != 0) : rem;
        return rem;
    }

    int implRead(char[] cbuf, int off, int end) throws IOException {

        // In order to handle surrogate pairs, this method requires that
        // the invoker attempt to read at least two characters.  Saving the
        // extra character, if any, at a higher level is easier than trying
        // to deal with it here.
        assert (end - off > 1);

        CharBuffer cb = CharBuffer.wrap(cbuf, off, end - off);
        if (cb.position() != 0) {
            // Ensure that cb[0] == cbuf[off]
            cb = cb.slice();
        }

        boolean eof = false;
        for (;;) {
            CoderResult cr = decoder.decode(bb, cb, eof);
            if (cr.isUnderflow()) {
                if (eof)
                    break;
                if (!cb.hasRemaining())
                    break;
                if ((cb.position() > 0) && !inReady())
                    break;          // Block at most once
                int n = readBytes();
                if (n < 0) {
                    eof = true;
                    if ((cb.position() == 0) && (!bb.hasRemaining()))
                        break;
                }
                continue;
            }
            if (cr.isOverflow()) {
                assert cb.position() > 0;
                break;
            }
            cr.throwException();
        }

        if (eof) {
            // ## Need to flush decoder
            decoder.reset();
        }

        if (cb.position() == 0) {
            if (eof) {
                return -1;
            }
            assert false;
        }
        return cb.position();
    }

    String encodingName() {
        return ((cs instanceof HistoricallyNamedCharset)
            ? ((HistoricallyNamedCharset)cs).historicalName()
            : cs.name());
    }

    private boolean inReady() {
        try {
            return (((in != null) && (in.available() > 0))
                    || (ch instanceof FileChannel)); // ## RBC.available()?
        } catch (IOException x) {
            return false;
        }
    }

    boolean implReady() {
        return bb.hasRemaining() || inReady();
    }

    void implClose() throws IOException {
        if (ch != null) {
            ch.close();
        } else {
            in.close();
        }
    }
}