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https://issues.apache.org/jira/browse/CODEC-130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13115318#comment-13115318
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James Pickering commented on CODEC-130:
---------------------------------------
I think what you're saying is that the current code conforms to the
FilterInputStream contract. I don't think this is the case.
At a practical level, the current behaviour isn't what other FilterInputStream
subclasses do. InflaterInputStream, for example (from the JDK standard class
library), skips over bytes of uncompressed (i.e, output) data.
At a theoretical level, we should be honoring the InputStream contract.
FilterInputStream is a convenience subclass, to simplify InputStream coding
(most FilterInputStream subclasses have a 1-1 correspondence between input and
output bytes, so FilterInputStream's behaviour is reasonable). An InputStream
is a stream of bytes that can be read, and consumers should not need to know
how it is implemented. If we continue with the current behaviour, we introduce
an implementation dependency, breaking OO encapsulation (indeed, I first
noticed this bug when some code that worked with other InputStreams broke with
Base64InputStream).
I take your point that existing code that relies on the current behaviour could
break as a result of the fix, but I can't imagine any correct code relying on
the current behaviour (it produces nonsense data if skip requests are not
multiples of 4, and aligned to 4 byte boundaries). At worst, we'd break
people's workarounds.
> Base64InputStream.skip skips underlying stream, not output
> ----------------------------------------------------------
>
> Key: CODEC-130
> URL: https://issues.apache.org/jira/browse/CODEC-130
> Project: Commons Codec
> Issue Type: Bug
> Affects Versions: 1.5
> Reporter: James Pickering
> Priority: Minor
> Attachments: base64snippet.java
>
>
> Base64InputStream.skip() skips within underlying stream, leading to
> unexpected behaviour.
> The following code will reproduce the issue:
> @Test
> public void testSkip() throws Throwable {
> InputStream ins =
> new
> ByteArrayInputStream("AAAA////".getBytes("ISO-8859-1"));//should decode to
> {0, 0, 0, 255, 255, 255}
> Base64InputStream instance = new Base64InputStream(ins);
> assertEquals(3L, instance.skip(3L)); //should skip 3 decoded characters,
> or 4 encoded characters
> assertEquals(255, instance.read()); //Currently returns 3, as it is
> decoding "A/", not "//"
> }
> The following code, if added to Base64InputStream, or (BaseNCodecInputStream
> in the dev build) would resolve the issue:
> @Override
> public long skip(long n) throws IOException {
> //delegate to read()
> long bytesRead = 0;
> while ((bytesRead < n) && (read() != -1)) {
> bytesRead++;
> }
> return bytesRead;
> }
> More efficient code may be possible.
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