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package org.jooby.internal;
import java.io.IOException;
import java.io.InputStream;
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;
/**
* {@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.
*
* 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 java.io.BufferedReader}.
*
* {@link ReaderInputStream} implements the inverse transformation of
* {@link java.io.InputStreamReader}; in the following example, reading from in2 would
* return the same byte sequence as reading from in (provided that the initial byte
* sequence is legal with respect to the charset encoding):
*
*
* InputStream in = ...
* Charset cs = ...
* InputStreamReader reader = new InputStreamReader(in, cs);
* ReaderInputStream in2 = new ReaderInputStream(reader, cs);
* {@link ReaderInputStream} implements the same transformation as
* {@link java.io.OutputStreamWriter}, except that the control flow is reversed: both classes
* transform a character stream into a byte stream, but {@link java.io.OutputStreamWriter} pushes
* data to the underlying stream, while {@link ReaderInputStream} pulls it from the underlying
* stream.
*
* 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, i.e. by providing a
* {@link Reader} instance. An example of a situation where this problem may appear is when
* implementing the {@link javax.activation.DataSource} interface from the Java Activation
* Framework.
*
* Given the fact that the {@link Reader} class doesn't provide any way to predict whether the next
* read operation will block or not, it is not possible to provide a meaningful implementation of
* the {@link InputStream#available()} method. A call to this method will always return 0. Also,
* this class doesn't support {@link InputStream#mark(int)}.
*
* Instances of {@link ReaderInputStream} are not thread safe.
*
* @author Andreas Veithen
* @since Commons IO 2.0
*/
public class ReaderInputStream extends InputStream {
private static final int DEFAULT_BUFFER_SIZE = 1024;
private final Reader reader;
private final CharsetEncoder encoder;
/**
* 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 = ByteBuffer.allocate(128);
private CoderResult lastCoderResult;
private boolean endOfInput;
/**
* Construct a new {@link ReaderInputStream}.
*
* @param reader the target {@link Reader}
* @param charset the charset encoding
* @param bufferSize the size of the input buffer in number of characters
*/
private ReaderInputStream(final Reader reader, final Charset charset, final int bufferSize) {
this.reader = reader;
encoder = charset.newEncoder();
encoderIn = CharBuffer.allocate(bufferSize);
encoderIn.flip();
}
/**
* Construct a new {@link ReaderInputStream} with a default input buffer size of
* 1024 characters.
*
* @param reader the target {@link Reader}
* @param charset the charset encoding
*/
public ReaderInputStream(final Reader reader, final Charset charset) {
this(reader, charset, DEFAULT_BUFFER_SIZE);
}
/**
* Read the specified number of bytes into an array.
*
* @param b 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 -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, int off, int len) throws IOException {
int read = 0;
while (len > 0) {
if (encoderOut.position() > 0) {
encoderOut.flip();
int c = Math.min(encoderOut.remaining(), len);
encoderOut.get(b, off, c);
off += c;
len -= c;
read += c;
encoderOut.compact();
} else {
if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
encoderIn.compact();
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).
int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
if (c == -1) {
endOfInput = true;
} else {
encoderIn.position(position + c);
}
encoderIn.flip();
}
lastCoderResult = encoder.encode(encoderIn, encoderOut, endOfInput);
if (endOfInput && encoderOut.position() == 0) {
break;
}
}
}
return read == 0 && endOfInput ? -1 : read;
}
/**
* Read the specified number of bytes into an array.
*
* @param b the byte array to read into
* @return the number of bytes read or -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);
}
/**
* Read a single byte.
*
* @return either the byte read or -1 if the end of the stream
* has been reached
* @throws IOException if an I/O error occurs
*/
@Override
public int read() throws IOException {
byte[] b = new byte[1];
return read(b) == -1 ? -1 : b[0] & 0xFF;
}
/**
* Close 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();
}
}