在試驗ZLib壓縮時,我遇到了一個奇怪的問題。如果源數組長度至少爲32752字節,則用隨機數據解壓縮zlib壓縮的字節數組將失敗。這裏有一個重現問題的小程序,你可以see it in action on IDEOne。壓縮和解壓縮方法是摘取教程的標準代碼。在大字節陣列上ZLib解壓縮失敗
public class ZlibMain {
private static byte[] compress(final byte[] data) {
final Deflater deflater = new Deflater();
deflater.setInput(data);
deflater.finish();
final byte[] bytesCompressed = new byte[Short.MAX_VALUE];
final int numberOfBytesAfterCompression = deflater.deflate(bytesCompressed);
final byte[] returnValues = new byte[numberOfBytesAfterCompression];
System.arraycopy(bytesCompressed, 0, returnValues, 0, numberOfBytesAfterCompression);
return returnValues;
}
private static byte[] decompress(final byte[] data) {
final Inflater inflater = new Inflater();
inflater.setInput(data);
try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length)) {
final byte[] buffer = new byte[Math.max(1024, data.length/10)];
while (!inflater.finished()) {
final int count = inflater.inflate(buffer);
outputStream.write(buffer, 0, count);
}
outputStream.close();
final byte[] output = outputStream.toByteArray();
return output;
} catch (DataFormatException | IOException e) {
throw new RuntimeException(e);
}
}
public static void main(final String[] args) {
roundTrip(100);
roundTrip(1000);
roundTrip(10000);
roundTrip(20000);
roundTrip(30000);
roundTrip(32000);
for (int i = 32700; i < 33000; i++) {
if(!roundTrip(i))break;
}
}
private static boolean roundTrip(final int i) {
System.out.printf("Starting round trip with size %d: ", i);
final byte[] data = new byte[i];
for (int j = 0; j < data.length; j++) {
data[j]= (byte) j;
}
shuffleArray(data);
final byte[] compressed = compress(data);
try {
final byte[] decompressed = CompletableFuture.supplyAsync(() -> decompress(compressed))
.get(2, TimeUnit.SECONDS);
System.out.printf("Success (%s)%n", Arrays.equals(data, decompressed) ? "matching" : "non-matching");
return true;
} catch (InterruptedException | ExecutionException | TimeoutException e) {
System.out.println("Failure!");
return false;
}
}
// Implementing Fisher–Yates shuffle
// source: https://stackoverflow.com/a/1520212/342852
static void shuffleArray(byte[] ar) {
Random rnd = ThreadLocalRandom.current();
for (int i = ar.length - 1; i > 0; i--) {
int index = rnd.nextInt(i + 1);
// Simple swap
byte a = ar[index];
ar[index] = ar[i];
ar[i] = a;
}
}
}
這是在zlib的一個已知的bug?或者我的壓縮/解壓縮例程有錯誤?
謝謝。正如所寫的,它不是我的代碼,我現在用代碼替換它。但是,要感謝關於代碼有什麼問題的啓發。 –
是個不錯的問題;我喜歡狩獵這樣的錯誤;-) –
非常好的調查! – nobeh