edu.berkeley.cs.jqf.fuzz.guidance.StreamBackedRandom Maven / Gradle / Ivy
/*
* Copyright (c) 2017-2018 The Regents of the University of California
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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package edu.berkeley.cs.jqf.fuzz.guidance;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Random;
/**
* This class extends {@link Random} to act as a generator of
* "random" values, which themselves are read from a static file.
*
* The file-backed random number generator can be used for tuning the
* "random" choices made by various junit-quickcheck
* generators using a mutation-based genetic algorithm, in order to
* maximize some objective function that can be measured from the
* execution of each trial, such as code coverage.
*
*
*/
public class StreamBackedRandom extends Random {
private final InputStream inputStream;
private final ByteBuffer byteBuffer = ByteBuffer.allocate(4);
private int totalBytesRead = 0;
private int leadingBytesToIgnore = 0;
/**
* Constructs a stream-backed random generator.
*
* Also sets the seed of the underlying pseudo-random number
* generator deterministically to zero.
*
* @param source a generator of "random" bytes
*/
public StreamBackedRandom(InputStream source) {
super(0x5DEECE66DL);
// Open the backing file source as a buffered input stream
this.inputStream = source;
// Force encoding to little-endian so that we can read small ints
// by reading partially into the start of the buffer
byteBuffer.order(ByteOrder.LITTLE_ENDIAN);
}
/**
* Convenience constructor for use with the junit-quickcheck framework.
*
* The junit-quickcheck SourceOfRandomness annoyingly reads 8 bytes of
* random data as soon as it is instantiated, only to configure its own
* seed. As the seed is meaningless here, the 8 bytes get wasted. For
* this purpose, this constructor allows specifying how many bytes of
* requested random data to skip before starting to read from file.
*
* @param source a generator of "random" bytes
* @param leadinBytesToIgnore the number of leading bytes to ignore
*/
public StreamBackedRandom(InputStream source, int leadinBytesToIgnore) {
this(source);
this.leadingBytesToIgnore = leadinBytesToIgnore;
}
/**
* Generates upto 32 bits of random data for internal use by the Random
* class.
*
* Attempts to read up to 4 bytes of data from the input file, and
* returns the requested lower order bits as a pseudo-random value.
*
* If end-of-file is reached before reading 4 bytes,
* an {@link IllegalStateException} is thrown.
*
* @param bits the number of random bits to retain (1 to 32 inclusive)
* @return the integer value whose lower bits bits contain the
* next random data available in the backing source
* @throws IllegalStateException if EOF has already been reached
*/
@Override
public int next(int bits) {
// Ensure that up to 32 bits are being requested
if (bits < 0 || bits > 32) {
throw new IllegalArgumentException("Must read 1-32 bits at a time");
}
// Zero out the byte buffer before reading from the source
byteBuffer.putInt(0, 0);
try {
// Read up to 4 bytes from the backing source
int maxBytesToRead = ((bits + 7) / 8);
assert(maxBytesToRead*8 >= bits && maxBytesToRead <= 4);
if (this.leadingBytesToIgnore > 0) {
int bytesToIgnore = Math.min(maxBytesToRead, this.leadingBytesToIgnore);
this.leadingBytesToIgnore -= bytesToIgnore;
maxBytesToRead -= bytesToIgnore;
}
// If fewer bytes are read (because EOF is reached), the buffer
// just keeps containing zeros
int actualBytesRead = inputStream.read(byteBuffer.array(), 0, maxBytesToRead);
totalBytesRead += actualBytesRead;
// If EOF was reached, throw an exception
if (actualBytesRead != maxBytesToRead) {
String message = String.format("EOF reached; total bytes read = %d, " +
"last read got %d of %d bytes",
totalBytesRead, actualBytesRead, maxBytesToRead);
throw new IllegalStateException(new EOFException(message));
}
} catch (IOException e) {
throw new GuidanceException(e);
}
// Interpret the bytes read as an integer
int value = byteBuffer.getInt(0);
// Return only the lower order bits as requested
int mask = bits < 32 ? (1 << bits) - 1 : -1;
return value & mask;
}
@Override
public int nextInt(int bound) {
if (bound <= 0)
throw new IllegalArgumentException("bound must be positive");
return next(31) % bound;
}
public byte nextByte() {
return (byte) next(Byte.SIZE);
}
public short nextShort() {
return (short) next(Short.SIZE);
}
public int getTotalBytesRead() {
return this.totalBytesRead;
}
}