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/*
* Copyright (C) 2012 The Android Open Source Project
*
* 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.jakewharton.disklrucache;
import java.io.ByteArrayOutputStream;
import java.io.Closeable;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
/**
* Buffers input from an {@link InputStream} for reading lines.
*
* <p>This class is used for buffered reading of lines. For purposes of this class, a line ends
* with "\n" or "\r\n". End of input is reported by throwing {@code EOFException}. Unterminated
* line at end of input is invalid and will be ignored, the caller may use {@code
* hasUnterminatedLine()} to detect it after catching the {@code EOFException}.
*
* <p>This class is intended for reading input that strictly consists of lines, such as line-based
* cache entries or cache journal. Unlike the {@link java.io.BufferedReader} which in conjunction
* with {@link java.io.InputStreamReader} provides similar functionality, this class uses different
* end-of-input reporting and a more restrictive definition of a line.
*
* <p>This class supports only charsets that encode '\r' and '\n' as a single byte with value 13
* and 10, respectively, and the representation of no other character contains these values.
* We currently check in constructor that the charset is one of US-ASCII, UTF-8 and ISO-8859-1.
* The default charset is US_ASCII.
*/
class StrictLineReader implements Closeable {
private static final byte CR = (byte) '\r';
private static final byte LF = (byte) '\n';
private final InputStream in;
private final Charset charset;
/*
* Buffered data is stored in {@code buf}. As long as no exception occurs, 0 <= pos <= end
* and the data in the range [pos, end) is buffered for reading. At end of input, if there is
* an unterminated line, we set end == -1, otherwise end == pos. If the underlying
* {@code InputStream} throws an {@code IOException}, end may remain as either pos or -1.
*/
private byte[] buf;
private int pos;
private int end;
/**
* Constructs a new {@code LineReader} with the specified charset and the default capacity.
*
* @param in the {@code InputStream} to read data from.
* @param charset the charset used to decode data. Only US-ASCII, UTF-8 and ISO-8859-1 are
* supported.
* @throws NullPointerException if {@code in} or {@code charset} is null.
* @throws IllegalArgumentException if the specified charset is not supported.
*/
public StrictLineReader(InputStream in, Charset charset) {
this(in, 8192, charset);
}
/**
* Constructs a new {@code LineReader} with the specified capacity and charset.
*
* @param in the {@code InputStream} to read data from.
* @param capacity the capacity of the buffer.
* @param charset the charset used to decode data. Only US-ASCII, UTF-8 and ISO-8859-1 are
* supported.
* @throws NullPointerException if {@code in} or {@code charset} is null.
* @throws IllegalArgumentException if {@code capacity} is negative or zero
* or the specified charset is not supported.
*/
public StrictLineReader(InputStream in, int capacity, Charset charset) {
if (in == null || charset == null) {
throw new NullPointerException();
}
if (capacity < 0) {
throw new IllegalArgumentException("capacity <= 0");
}
if (!(charset.equals(Util.US_ASCII))) {
throw new IllegalArgumentException("Unsupported encoding");
}
this.in = in;
this.charset = charset;
buf = new byte[capacity];
}
/**
* Closes the reader by closing the underlying {@code InputStream} and
* marking this reader as closed.
*
* @throws IOException for errors when closing the underlying {@code InputStream}.
*/
public void close() throws IOException {
synchronized (in) {
if (buf != null) {
buf = null;
in.close();
}
}
}
/**
* Reads the next line. A line ends with {@code "\n"} or {@code "\r\n"},
* this end of line marker is not included in the result.
*
* @return the next line from the input.
* @throws IOException for underlying {@code InputStream} errors.
* @throws EOFException for the end of source stream.
*/
public String readLine() throws IOException {
synchronized (in) {
if (buf == null) {
throw new IOException("LineReader is closed");
}
// Read more data if we are at the end of the buffered data.
// Though it's an error to read after an exception, we will let {@code fillBuf()}
// throw again if that happens; thus we need to handle end == -1 as well as end == pos.
if (pos >= end) {
fillBuf();
}
// Try to find LF in the buffered data and return the line if successful.
for (int i = pos; i != end; ++i) {
if (buf[i] == LF) {
int lineEnd = (i != pos && buf[i - 1] == CR) ? i - 1 : i;
String res = new String(buf, pos, lineEnd - pos, charset.name());
pos = i + 1;
return res;
}
}
// Let's anticipate up to 80 characters on top of those already read.
ByteArrayOutputStream out = new ByteArrayOutputStream(end - pos + 80) {
@Override
public String toString() {
int length = (count > 0 && buf[count - 1] == CR) ? count - 1 : count;
try {
return new String(buf, 0, length, charset.name());
} catch (UnsupportedEncodingException e) {
throw new AssertionError(e); // Since we control the charset this will never happen.
}
}
};
while (true) {
out.write(buf, pos, end - pos);
// Mark unterminated line in case fillBuf throws EOFException or IOException.
end = -1;
fillBuf();
// Try to find LF in the buffered data and return the line if successful.
for (int i = pos; i != end; ++i) {
if (buf[i] == LF) {
if (i != pos) {
out.write(buf, pos, i - pos);
}
pos = i + 1;
return out.toString();
}
}
}
}
}
public boolean hasUnterminatedLine() {
return end == -1;
}
/**
* Reads new input data into the buffer. Call only with pos == end or end == -1,
* depending on the desired outcome if the function throws.
*/
private void fillBuf() throws IOException {
int result = in.read(buf, 0, buf.length);
if (result == -1) {
throw new EOFException();
}
pos = 0;
end = result;
}
}
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