[jira] [Commented] (ARROW-17107) [Java] JSONFileWriter throws IOOBE writing an empty list

["David Li (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-17107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17568038#comment-17568038 ] 

David Li commented on ARROW-17107:
----------------------------------

Note that the JSON writer won't construct JSONL as you might expect, it's actually there to generate an internal format for our integration tests - so maybe we should note the stability/scope more explicitly in the docs. But we should probably still fix this regardless while making that more clear.

CC [~dsusanibara]

> [Java] JSONFileWriter throws IOOBE writing an empty list
> --------------------------------------------------------
>
>                 Key: ARROW-17107
>                 URL: https://issues.apache.org/jira/browse/ARROW-17107
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Java
>    Affects Versions: 8.0.0
>            Reporter: James Henderson
>            Priority: Minor
>
> Hey folks,
> I'm trying to write an empty ListVector out through the `JsonFileWriter`, and am getting an IOOBE. Stack trace is as follows:
>  
> ```
> java.lang.IndexOutOfBoundsException: index: 0, length: 4 (expected: range(0, 0))
>  at org.apache.arrow.memory.ArrowBuf.checkIndexD (ArrowBuf.java:318)
>     org.apache.arrow.memory.ArrowBuf.chk (ArrowBuf.java:305)
>     org.apache.arrow.memory.ArrowBuf.getInt (ArrowBuf.java:424)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeValueToGenerator (JsonFileWriter.java:270)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeFromVectorIntoJson (JsonFileWriter.java:237)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeFromVectorIntoJson (JsonFileWriter.java:253)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeFromVectorIntoJson (JsonFileWriter.java:253)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeFromVectorIntoJson (JsonFileWriter.java:253)
>     org.apache.arrow.vector.ipc.JsonFileWriter.writeBatch (JsonFileWriter.java:200)
>     org.apache.arrow.vector.ipc.JsonFileWriter.write (JsonFileWriter.java:190)
> ```
> It's trying to write the offset buffer of the list, which is empty. L224 of JFW.java sets `bufferValueCount` to 1 (because we're not a DUV), so we enter the `for` loop. We don't hit the `valueCount=0` condition in L230 (because we're not a varbinary or a varchar vector). So we fall into the `else`, which tries to write the 0th element in the offset vector, and IOOBE.
> Could we include 'list' in either the L224 or the L230 checks?
> Admittedly, I'm not aware of the history of this section, but it seems that, by the time we hit L230 (i.e. excluding DUV), any empty vector should yield a single 0?
> Let me know if there's any more info I can provide!
> Cheers,
> James



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