java - 这是 Java 的 Inflater 中的错误还是什么？

Question

我在一些单元测试中被这个咬伤了。

我想解压缩一些 ZLIB 压缩的数据，使用 Inflater ，其中原始数据长度是预先知道的。

这(直接)按预期工作

    /*  
     * Decompresses a zlib compressed buffer, with given size of raw data.
     * All data is fed and inflated in full (one step) 
     */
    public static byte[] decompressFull(byte[] comp, int len) throws Exception {
        byte[] res = new byte[len]; // result (uncompressed)
        Inflater inf = new Inflater();
        inf.setInput(comp);
        int n = inf.inflate(res, 0, len);
        if (n != len)
            throw new RuntimeException("didn't inflate all data");
        System.out.println("Data done (full). bytes in :"  + inf.getBytesRead() 
                + " out=" + inf.getBytesWritten()
                + " finished: " + inf.finished());
        // done - the next is not needed, just for checking... 
        //try a final inflate just in case (might trigger ZLIB crc check)
        byte[] buf2 = new byte[6];
        int nx = inf.inflate(buf2);//should give 0
        if (nx != 0)
            throw new RuntimeException("nx=" + nx + " " + Arrays.toString(buf2));
        if (!inf.finished())
            throw new RuntimeException("not finished?");
        inf.end();
        return res;
    }

现在，压缩输入可以任意大小的 block 。下面的代码模拟了压缩输入除了最后 4 个字节外全部送入，然后其余字节一次送入一个的情况。 (据我了解，解压缩完整数据不需要 zlib 流的最后 4 个或 5 个字节，但需要它们来检查完整性 - Adler-32 CRC)。

    public static byte[] decompressBytexByte(byte[] comp, int len) throws Exception {
            byte[] res = new byte[len]; // result (uncompressed)
            Inflater inf = new Inflater();
            inf.setInput(comp, 0, comp.length - 4);
            int n = inf.inflate(res, 0, len);
            if (n != len)
                throw new RuntimeException("didn't inflate all data");
            // inf.setInput(comp, comp.length-4,4); 
            // !!! works if I uncomment the line befor and comment the next for 
            for (int p = comp.length - 4; p < comp.length; p++)
                inf.setInput(comp, p, 1);
            System.out.println("Data done (decompressBytexByte). bytes in :" + inf.getBytesRead() 
                    + " out=" + inf.getBytesWritten() + " finished: " + inf.finished());
            // all data fed... try a final inflate (might -should?- trigger ZLIB crc check)
            byte[] buf2 = new byte[6];
            int nx = inf.inflate(buf2);//should give 0
            if (nx != 0)
                throw new RuntimeException("nx=" + nx + " " + Arrays.toString(buf2));
            if (!inf.finished())
                throw new RuntimeException("not finished?");
            inf.end();
            return res;
        }

好吧，这对我不起作用(Java 1.8.0_181)。似乎充气机还没有完成，阿德勒 CRC 校验也没有完成；更多:似乎字节没有被送入充气机。

更奇怪的是:如果尾随的 4 个字节是在一次调用中输入的，它就可以工作。

您可以在这里尝试:https://repl.it/@HernanJJ/Inflater-Test

当我一次输入一个字节时，甚至会发生更奇怪的事情:有时行 int nx= inf.inflate(buf2);//should give 0 return non-zero (当所有数据都已经膨胀时)。

这是预期的行为吗？我错过了什么吗？

Answer 1

正如 @SeanBright 已经注意到的那样，您应该只在 Inflater.needsInput() 返回 true 时为其提供新的输入。

setInput 的顺序调用会覆盖您之前传递的输入。

Javadoc of Inflater.needsInput() :

Returns true if no data remains in the input buffer. This can be used to determine if #setInput should be called in order to provide more input.

只要您按字节输入它，情况总是如此，因此您可以跳过检查本身。

您可以将 decompressBytexByte 方法的输入设置部分替换为以下内容(对于完整的逐字节馈送):

byte[] res = new byte[len];
Inflater inf = new Inflater();

int a = 0; // number of bytes that have already been obtained
for (int p = 0; p < comp.length; p++) {         
    inf.setInput(comp, p, 1);
    a += inf.inflate(res, a, len - a);
}