FileFuzzer.groovy

import java.nio.ByteBuffer
import java.nio.channels.SeekableByteChannel
import java.nio.file.Files
import java.nio.file.Path
import java.nio.file.Paths
import java.security.SecureRandom

class FileFuzzer {
    private static final Random random = new SecureRandom()

    static void main(String[] args) {
        iterate(Paths.get(args[0]), args[1] as int, args[2] as int)
    }

    static void iterate(final Path sourceFile, final int count, final int start = 1) {
        for (int i = start; i < count; i++) {
            final resultName = "fuzz_${i}_${sourceFile.fileName.toString()}"
            final resultFile = sourceFile.resolveSibling(resultName)
            Files.copy(sourceFile, resultFile)
            mutate(resultFile)
        }
    }

    static void mutate(final Path file, final int chunkCapacity = 1024 * 4) {
        final long size = Files.size(file)
        final long start = size * random.nextDouble()
        final long length = (size - start) * random.nextDouble()
        final int count = Math.floorDiv(length, chunkCapacity)
        final int remaining = Math.floorMod(length, chunkCapacity)

        final channel = Files.newByteChannel(file)
        channel.position(start)
        write(channel, remaining)
        write(channel, chunkCapacity, count)
        channel.close()
    }

    static void write(SeekableByteChannel channel, int size, int count = 1) {
        final buffer = ByteBuffer.allocateDirect(size)
        for (int i = 0; i < count; i++) {
            random.nextBytes(buffer.array())
            channel.write(buffer)
        }
    }
}