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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-10134) UTF-16 support for TextInputFormat
Date Mon, 08 Oct 2018 07:39:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-10134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16641470#comment-16641470
] 

ASF GitHub Bot commented on FLINK-10134:
----------------------------------------

fhueske commented on a change in pull request #6710: [FLINK-10134] UTF-16 support for TextInputFormat
bug fixed
URL: https://github.com/apache/flink/pull/6710#discussion_r223268822
 
 

 ##########
 File path: flink-core/src/main/java/org/apache/flink/api/common/io/FileInputFormat.java
 ##########
 @@ -601,41 +602,44 @@ public LocatableInputSplitAssigner getInputSplitAssigner(FileInputSplit[]
splits
 		if (unsplittable) {
 			int splitNum = 0;
 			for (final FileStatus file : files) {
+				String bomCharsetName = getBomCharset(file);
 
 Review comment:
   Yes, I'm aware of that. It would also be required for every split unless we cache the BOM
per file.
   OTOH, if we do it in the JM, the job cannot start until a single thread had a look at the
first bytes of each file.

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> UTF-16 support for TextInputFormat
> ----------------------------------
>
>                 Key: FLINK-10134
>                 URL: https://issues.apache.org/jira/browse/FLINK-10134
>             Project: Flink
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 1.4.2
>            Reporter: David Dreyfus
>            Priority: Blocker
>              Labels: pull-request-available
>
> It does not appear that Flink supports a charset encoding of "UTF-16". It particular,
it doesn't appear that Flink consumes the Byte Order Mark (BOM) to establish whether a UTF-16
file is UTF-16LE or UTF-16BE.
>  
> TextInputFormat.setCharset("UTF-16") calls DelimitedInputFormat.setCharset(), which sets
TextInputFormat.charsetName and then modifies the previously set delimiterString to construct
the proper byte string encoding of the the delimiter. This same charsetName is also used in
TextInputFormat.readRecord() to interpret the bytes read from the file.
>  
> There are two problems that this implementation would seem to have when using UTF-16.
>  # delimiterString.getBytes(getCharset()) in DelimitedInputFormat.java will return a
Big Endian byte sequence including the Byte Order Mark (BOM). The actual text file will not
contain a BOM at each line ending, so the delimiter will never be read. Moreover, if the actual
byte encoding of the file is Little Endian, the bytes will be interpreted incorrectly.
>  # TextInputFormat.readRecord() will not see a BOM each time it decodes a byte sequence
with the String(bytes, offset, numBytes, charset) call. Therefore, it will assume Big Endian,
which may not always be correct. [1] [https://github.com/apache/flink/blob/master/flink-java/src/main/java/org/apache/flink/api/java/io/TextInputFormat.java#L95]
>  
> While there are likely many solutions, I would think that all of them would have to start
by reading the BOM from the file when a Split is opened and then using that BOM to modify
the specified encoding to a BOM specific one when the caller doesn't specify one, and to overwrite
the caller's specification if the BOM is in conflict with the caller's specification. That
is, if the BOM indicates Little Endian and the caller indicates UTF-16BE, Flink should rewrite
the charsetName as UTF-16LE.
>  I hope this makes sense and that I haven't been testing incorrectly or misreading the
code.
>  
> I've verified the problem on version 1.4.2. I believe the problem exists on all versions. 



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