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// Licensed to the Software Freedom Conservancy (SFC) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The SFC 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
//
// 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 org.openqa.selenium.json;
import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;
import org.openqa.selenium.internal.Require;
/**
* Similar to a {@link Reader} but with the ability to peek a single character ahead.
*
* For the sake of providing a useful {@link #toString()} implementation, keeps the most recently
* read characters in the input buffer.
*/
class Input {
/** end-of-file indicator (0xFFFD) */
public static final char EOF = (char) -1; // NOTE: Produces Unicode replacement character (0xFFFD)
/** the number of chars to buffer */
private static final int BUFFER_SIZE = 4096;
/** the number of chars to remember, safe to set to 0 */
private static final int MEMORY_SIZE = 128;
private final Reader source;
/** a buffer used to minimize read calls and to keep the chars to remember */
private final char[] buffer;
/** the filled area in the buffer */
private int filled;
/** the last position read in the buffer */
private int position;
/**
* Initialize a new instance of the {@link Input} class with the specified source.
*
* @param source {@link Reader} object that supplies the input to be processed
*/
public Input(Reader source) {
this.source = Require.nonNull("Source", source);
this.buffer = new char[BUFFER_SIZE + MEMORY_SIZE];
this.filled = 0;
this.position = -1;
}
/**
* Extract the next character from the input without consuming it.
*
* @return the next input character; {@link #EOF} if input is exhausted
*/
public char peek() {
return fill() ? buffer[position + 1] : EOF;
}
/**
* Read and consume the next character from the input.
*
* @return the next input character; {@link #EOF} if input is exhausted
*/
public char read() {
return fill() ? buffer[++position] : EOF;
}
/**
* Return a string containing the most recently consumed input characters.
*
* @return {@link String} with up to 128 consumed input characters
*/
@Override
public String toString() {
int offset;
int length;
if (position < MEMORY_SIZE) {
offset = 0;
length = position + 1;
} else {
offset = position + 1 - MEMORY_SIZE;
length = MEMORY_SIZE;
}
return "Last " + length + " characters read: " + new String(buffer, offset, length);
}
/**
* If all buffered input has been consumed, read the next chunk into the buffer.
* NOTE: The last 128 character of consumed input is retained for debug output.
*
* @return {@code true} if new input is available; {@code false} if input is exhausted
* @throws UncheckedIOException if an I/O exception is encountered
*/
private boolean fill() {
// do we need to fill the buffer?
while (filled == position + 1) {
try {
// free the buffer, keep only the chars to remember
int shift = filled - MEMORY_SIZE;
if (shift > 0) {
position -= shift;
filled -= shift;
System.arraycopy(buffer, shift, buffer, 0, filled);
}
// try to fill the buffer
int n = source.read(buffer, filled, buffer.length - filled);
if (n == -1) {
// EOF reached
return false;
} else {
// n might be 0, the outer loop will handle this
filled += n;
}
} catch (IOException e) {
throw new UncheckedIOException(e.getMessage(), e);
}
}
return true;
}
}