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https://issues.apache.org/jira/browse/FLINK-10134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16656173#comment-16656173
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ASF GitHub Bot commented on FLINK-10134:
----------------------------------------
XuQianJin-Stars commented on a change in pull request #6823: [FLINK-10134]
UTF-16 support for TextInputFormat bug refixed
URL: https://github.com/apache/flink/pull/6823#discussion_r226516362
##########
File path:
flink-core/src/main/java/org/apache/flink/api/common/io/DelimitedInputFormat.java
##########
@@ -472,6 +498,7 @@ public void open(FileInputSplit split) throws IOException {
this.offset = splitStart;
if (this.splitStart != 0) {
+ setBomFileCharset(split);
Review comment:
I have two questions about this commit, as follows:
For the first suggestion, I feel that users often cannot know the encoding
of the file accurately. For example: file encoding `UTF-16LE`, with bom header,
user-specified encoding `UTF-16BE` will report an error. And there is bom UTF
with bom encoding I believe will be the majority. So I think it is necessary to
do the bom code detection first, which is better for the user experience.
For the fourth recommendation, the seek of `GenericCsvInputFormat` cannot be
seek to position 0. It calls the `seek` method of `InputStreamFSInputWrapper`.
This method cannot currently seek to position 0.
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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: Critical
> 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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