viliam-durina opened a new issue, #15730:
URL: https://github.com/apache/lucene/issues/15730
### Description
The absolute read methods in `RandomAccessInput` should read from the given
position, and not use or modify the input's position. However
`MemorySegmentIndexInput`'s absolute `read` methods modify the input's position
if the read happens at the segment boundary, because if the value can't be read
from a single segment, the implementation falls back to seek + relative read.
The following test reproduces it:
```java
public class TestMemorySegmentIndexInput extends LuceneTestCase {
public void testPositionNotModifiedAtBoundary() throws IOException {
try (Arena arena = Arena.ofConfined()) {
MemorySegment seg1 = arena.allocate(16);
MemorySegment seg2 = arena.allocate(16);
try (MemorySegmentIndexInput input =
MemorySegmentIndexInput.newInstance("", arena,
new MemorySegment[] {seg1, seg2}, 32, 4, false, null)) {
input.readInt(4);
assertEquals(0, input.getFilePointer());
input.readInt(14);
assertEquals(0, input.getFilePointer()); // this fails, position is
now 18
}
}
}
}
```
Perhaps it's not an actual issue, I don't know if Lucene combines relative
and absolute reads anywhere and relies on the position not being changed by the
absolute read, and even if it does, multiple segments are used if the file is
larger than 16GB, so it's very unlikely. But it should be fixed anyway I think,
because the root cause will be very hard to figure out should it happen.
### Version and environment details
_No response_
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