[jira] [Commented] (HADOOP-15606) FSDataInputStream/FSInputStream to implement getFileLength()

["Steve Loughran (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-15606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16653459#comment-16653459 ] 

Steve Loughran commented on HADOOP-15606:
-----------------------------------------

DFSInputStream already implements a {{getFileLength()}} call; this could be propagated up, at least with its current signature (returns: long). FWIW, I'd prefer Optional as you can do more

> FSDataInputStream/FSInputStream to implement getFileLength()
> ------------------------------------------------------------
>
>                 Key: HADOOP-15606
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15606
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs, fs/s3
>    Affects Versions: 3.1.0
>            Reporter: Steve Loughran
>            Priority: Major
>
> server-side transcoding, predicate-pushdown filtering in storage, client-side decryption can all result in an input stream shorter or longer than the file size as measured in getFileStatus/listFiles/listStatus. 
> Assuming the length is known once open() returns, the FSDataInputStream can return the length of the data, which can then be used for accurate seeks within the data.
> * requires the streams to know their length; easy to check (hasCapabilities), or make the new method return an Optional<Long>, but caller will need to (a) look for this if present and (b) fall back.
> * Could be rolled out for all our own clients/connectors, would take time for others



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