Shenjiaqi commented on code in PR #20860:
URL: https://github.com/apache/flink/pull/20860#discussion_r990609029
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flink-runtime/src/main/java/org/apache/flink/runtime/state/memory/ByteStreamStateHandle.java:
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@@ -148,7 +148,7 @@ public int read(byte[] b, int off, int len) throws
IOException {
index += bytesToCopy;
return bytesToCopy;
} else {
- return -1;
+ return len == 0 ? 0 : -1;
Review Comment:
> Thanks for pointing this out, after rethinking the semantics of `read()`,
I think changing the
[NoFetchingInput#readBytes()](https://github.com/apache/flink/blob/9d2ae5572897f3e2d9089414261a250cfc2a2ab8/flink-core/src/main/java/org/apache/flink/api/java/typeutils/runtime/NoFetchingInput.java#L115-L140)
is a better way to go.
>
> As
https://docs.oracle.com/javase/8/docs/api/java/io/FileInputStream.html#read--
explained,
>
> > Returns:
> > the total number of bytes read into the buffer, or -1 if there is no
more data because the end of the file has been reached.
>
> We should keep the semantics of `read()` consistent.
ByteStateHandleInputstream extends FSDataInputStream, which actually extends
InputStream. So I think we should refer to
https://docs.oracle.com/javase/8/docs/api/java/io/InputStream.html read(byte[]
b, int off, int len). In the doc says "If len is zero, then no bytes are read
and 0 is returned". I also refer to the implementation of
[InputStream#read](https://github.com/openjdk/jdk/blob/jdk-18+37/src/java.base/share/classes/java/io/InputStream.java#L278-L282),
it first make sure len <= b.length - off, then return 0 if len is 0, event if
off == b.length.
As for doc of FileInputStream, we should refer to read(byte[] b, int off,
int len) instead of read(), and it says "If len is not zero, the method blocks
until some input is available; otherwise, no bytes are read and 0 is returned."
So this change actually fix the semantic right.
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