ReaderInputStream.java
/*
* Copyright (C) 2015 The Guava Authors
*
* 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 com.google.common.io;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.primitives.UnsignedBytes;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.nio.Buffer;
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.Arrays;
/**
* An {@link InputStream} that converts characters from a {@link Reader} into bytes using an
* arbitrary Charset.
*
* <p>This is an alternative to copying the data to an {@code OutputStream} via a {@code Writer},
* which is necessarily blocking. By implementing an {@code InputStream} it allows consumers to
* "pull" as much data as they can handle, which is more convenient when dealing with flow
* controlled, async APIs.
*
* @author Chris Nokleberg
*/
@GwtIncompatible
@ElementTypesAreNonnullByDefault
final class ReaderInputStream extends InputStream {
private final Reader reader;
private final CharsetEncoder encoder;
private final byte[] singleByte = new byte[1];
/**
* charBuffer holds characters that have been read from the Reader but not encoded yet. The buffer
* is perpetually "flipped" (unencoded characters between position and limit).
*/
private CharBuffer charBuffer;
/**
* byteBuffer holds encoded characters that have not yet been sent to the caller of the input
* stream. When encoding it is "unflipped" (encoded bytes between 0 and position) and when
* draining it is flipped (undrained bytes between position and limit).
*/
private ByteBuffer byteBuffer;
/** Whether we've finished reading the reader. */
private boolean endOfInput;
/** Whether we're copying encoded bytes to the caller's buffer. */
private boolean draining;
/** Whether we've successfully flushed the encoder. */
private boolean doneFlushing;
/**
* Creates a new input stream that will encode the characters from {@code reader} into bytes using
* the given character set. Malformed input and unmappable characters will be replaced.
*
* @param reader input source
* @param charset character set used for encoding chars to bytes
* @param bufferSize size of internal input and output buffers
* @throws IllegalArgumentException if bufferSize is non-positive
*/
ReaderInputStream(Reader reader, Charset charset, int bufferSize) {
this(
reader,
charset
.newEncoder()
.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE),
bufferSize);
}
/**
* Creates a new input stream that will encode the characters from {@code reader} into bytes using
* the given character set encoder.
*
* @param reader input source
* @param encoder character set encoder used for encoding chars to bytes
* @param bufferSize size of internal input and output buffers
* @throws IllegalArgumentException if bufferSize is non-positive
*/
ReaderInputStream(Reader reader, CharsetEncoder encoder, int bufferSize) {
this.reader = checkNotNull(reader);
this.encoder = checkNotNull(encoder);
checkArgument(bufferSize > 0, "bufferSize must be positive: %s", bufferSize);
encoder.reset();
charBuffer = CharBuffer.allocate(bufferSize);
Java8Compatibility.flip(charBuffer);
byteBuffer = ByteBuffer.allocate(bufferSize);
}
@Override
public void close() throws IOException {
reader.close();
}
@Override
public int read() throws IOException {
return (read(singleByte) == 1) ? UnsignedBytes.toInt(singleByte[0]) : -1;
}
// TODO(chrisn): Consider trying to encode/flush directly to the argument byte
// buffer when possible.
@Override
public int read(byte[] b, int off, int len) throws IOException {
// Obey InputStream contract.
checkPositionIndexes(off, off + len, b.length);
if (len == 0) {
return 0;
}
// The rest of this method implements the process described by the CharsetEncoder javadoc.
int totalBytesRead = 0;
boolean doneEncoding = endOfInput;
DRAINING:
while (true) {
// We stay in draining mode until there are no bytes left in the output buffer. Then we go
// back to encoding/flushing.
if (draining) {
totalBytesRead += drain(b, off + totalBytesRead, len - totalBytesRead);
if (totalBytesRead == len || doneFlushing) {
return (totalBytesRead > 0) ? totalBytesRead : -1;
}
draining = false;
Java8Compatibility.clear(byteBuffer);
}
while (true) {
// We call encode until there is no more input. The last call to encode will have endOfInput
// == true. Then there is a final call to flush.
CoderResult result;
if (doneFlushing) {
result = CoderResult.UNDERFLOW;
} else if (doneEncoding) {
result = encoder.flush(byteBuffer);
} else {
result = encoder.encode(charBuffer, byteBuffer, endOfInput);
}
if (result.isOverflow()) {
// Not enough room in output buffer--drain it, creating a bigger buffer if necessary.
startDraining(true);
continue DRAINING;
} else if (result.isUnderflow()) {
// If encoder underflows, it means either:
// a) the final flush() succeeded; next drain (then done)
// b) we encoded all of the input; next flush
// c) we ran of out input to encode; next read more input
if (doneEncoding) { // (a)
doneFlushing = true;
startDraining(false);
continue DRAINING;
} else if (endOfInput) { // (b)
doneEncoding = true;
} else { // (c)
readMoreChars();
}
} else if (result.isError()) {
// Only reach here if a CharsetEncoder with non-REPLACE settings is used.
result.throwException();
return 0; // Not called.
}
}
}
}
/** Returns a new CharBuffer identical to buf, except twice the capacity. */
private static CharBuffer grow(CharBuffer buf) {
char[] copy = Arrays.copyOf(buf.array(), buf.capacity() * 2);
CharBuffer bigger = CharBuffer.wrap(copy);
Java8Compatibility.position(bigger, buf.position());
Java8Compatibility.limit(bigger, buf.limit());
return bigger;
}
/** Handle the case of underflow caused by needing more input characters. */
private void readMoreChars() throws IOException {
// Possibilities:
// 1) array has space available on right hand side (between limit and capacity)
// 2) array has space available on left hand side (before position)
// 3) array has no space available
//
// In case 2 we shift the existing chars to the left, and in case 3 we create a bigger
// array, then they both become case 1.
if (availableCapacity(charBuffer) == 0) {
if (charBuffer.position() > 0) {
// (2) There is room in the buffer. Move existing bytes to the beginning.
Java8Compatibility.flip(charBuffer.compact());
} else {
// (3) Entire buffer is full, need bigger buffer.
charBuffer = grow(charBuffer);
}
}
// (1) Read more characters into free space at end of array.
int limit = charBuffer.limit();
int numChars = reader.read(charBuffer.array(), limit, availableCapacity(charBuffer));
if (numChars == -1) {
endOfInput = true;
} else {
Java8Compatibility.limit(charBuffer, limit + numChars);
}
}
/** Returns the number of elements between the limit and capacity. */
private static int availableCapacity(Buffer buffer) {
return buffer.capacity() - buffer.limit();
}
/**
* Flips the buffer output buffer so we can start reading bytes from it. If we are starting to
* drain because there was overflow, and there aren't actually any characters to drain, then the
* overflow must be due to a small output buffer.
*/
private void startDraining(boolean overflow) {
Java8Compatibility.flip(byteBuffer);
if (overflow && byteBuffer.remaining() == 0) {
byteBuffer = ByteBuffer.allocate(byteBuffer.capacity() * 2);
} else {
draining = true;
}
}
/**
* Copy as much of the byte buffer into the output array as possible, returning the (positive)
* number of characters copied.
*/
private int drain(byte[] b, int off, int len) {
int remaining = Math.min(len, byteBuffer.remaining());
byteBuffer.get(b, off, remaining);
return remaining;
}
}