android - 为什么 BufferedInputStream.read() 在 Android Nougat 用于返回 0 时返回 -1？

Question

在 Android N 设备上测试我的应用程序时，我发现我有许多与我使用 BufferedInputStream 的方式相关的新问题。问题似乎是我如何解释 BufferedInputStream.read() 的返回值。如果返回 0，我假设可以从底层流中读取 0 个字节，如果返回 -1，我假设底层流已经到达文件末尾(并退出读取)。这在牛轧糖之前一直有效。现在，当底层 InputStream.read() 返回 0 时，BufferedInputStream.read() 返回 -1。什么是正确的行为？为什么会这样？

这是一个精炼的例子......

   class ZeroBytesReadInputStream extends InputStream {
        ...
        @Override
        public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {
            return 0;
        }
    }

    private int testZeroBytesReadBufferedInputStream() {
        InputStream inputStream = new ZeroBytesReadInputStream();
        BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
        int valueReturned = 0;
        try {
            byte[] toStream = new byte[100];
            valueReturned = bufferedInputStream.read(toStream, 0, 100);
            Log.d("Zero Bytes Read Test", "BufferedInputStream returned = " + valueReturned + ". Android Version = " + android.os.Build.VERSION.SDK_INT);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return valueReturned;
    }

运行时的输出 -10-19 09:28:51.970 9138 9138 D 零字节读取测试:BufferedInputStream 返回 = -1。 Android 版本 = 24

10-19 09:32:19.200 12675 12675 D 零字节读取测试:BufferedInputStream 返回 = 0。Android 版本 = 23

Answer 1

根据 InputStream.read(byte[] b, int off, int len) 的文档，该方法实际上不应该返回 0，除非 len 参数为 0:

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

因此，底层流的实现是有问题的，因此 BufferedInputStream 的行为是不确定的。