[jira] [Comment Edited] (TIKA-2771) enableInputFilter() wrecks charset detection for some short html documents

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[jira] [Comment Edited] (TIKA-2771) enableInputFilter() wrecks charset detection for some short html documents

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    [ https://issues.apache.org/jira/browse/TIKA-2771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16675828#comment-16675828 ]

Hans Brende edited comment on TIKA-2771 at 11/5/18 10:44 PM:
-------------------------------------------------------------

[~[hidden email]] Ah, you're correct as regards the byteMap. The TODO comment threw me.

However, on closer inspection of the IBM500 byteMap, I see an even more alarming issue: Only 0x40 should map to 0x20, but the byteMap actually maps 118 out of the 256 bytes map to 0x20!!! (Including 0x20 itself, which is *not* a space, but rather a control character in IBM500!)

This could explain why so many false positives for IBM500 are occurring: *all special characters are mapped to spaces, which are then simply ignored by the n-gram detector*. But in order to have accurate n-gram measurements, those special characters need to be included in the calculations, I believe. Perhaps they should be mapped to 0x00 instead of 0x20?


was (Author: hansbrende):
[~[hidden email]] Ah, you're correct as regards the byteMap. The TODO comment threw me.

However, on closer inspection of the IBM500 byteMap, I see an even more alarming issue: 118 out of the 256 bytes map to 0x20!!!

But only 0x40 should map to 0x20.

This could explain why so many false positives for IBM500 are occurring: *all special characters are mapped to spaces, and then simply ignored*. But in order to have accurate n-gram measurements, those special characters need to be included in the calculations, I believe. I'm not sure, but perhaps they should be mapped to 0x00 instead of 0x20?



> enableInputFilter() wrecks charset detection for some short html documents
> --------------------------------------------------------------------------
>
>                 Key: TIKA-2771
>                 URL: https://issues.apache.org/jira/browse/TIKA-2771
>             Project: Tika
>          Issue Type: Bug
>          Components: detector
>    Affects Versions: 1.19.1
>            Reporter: Hans Brende
>            Priority: Critical
>
> When I try to run the CharsetDetector on http://w3c.github.io/microdata-rdf/tests/0065.html I get the very strange most confident result of "IBM500" with a confidence of 60 when I enable the input filter, *even if I set the declared encoding to UTF-8*.
> This can be replicated with the following code:
> {code:java}
> CharsetDetector detect = new CharsetDetector();
> detect.enableInputFilter(true);
> detect.setDeclaredEncoding("UTF-8");
> detect.setText(("<!DOCTYPE html>\n" +
>         "<div>\n" +
>         "  <div itemscope itemtype=\"http://schema.org/Person\" id=\"amanda\" itemref=\"a b\"></div>\n" +
>         "  <p id=\"a\">Name: <span itemprop=\"name\">Amanda</span></p>\n" +
>         "  <p id=\"b\" itemprop=\"band\">Jazz Band</p>\n" +
>         "</div>").getBytes(StandardCharsets.UTF_8));
> Arrays.stream(detect.detectAll()).forEach(System.out::println);
> {code}
> which prints:
> {noformat}
> Match of IBM500 in fr with confidence 60
> Match of UTF-8 with confidence 57
> Match of ISO-8859-9 in tr with confidence 50
> Match of ISO-8859-1 in en with confidence 50
> Match of ISO-8859-2 in cs with confidence 12
> Match of Big5 in zh with confidence 10
> Match of EUC-KR in ko with confidence 10
> Match of EUC-JP in ja with confidence 10
> Match of GB18030 in zh with confidence 10
> Match of Shift_JIS in ja with confidence 10
> Match of UTF-16LE with confidence 10
> Match of UTF-16BE with confidence 10
> {noformat}
> Note that if I do not set the declared encoding to UTF-8, the result is even worse, with UTF-8 falling from a confidence of 57 to 15.
> This is screwing up 1 out of 84 of my online microdata extraction tests over in Any23 (as that particular page is being rendered into complete gibberish), so I had to implement some hacky workarounds which I'd like to remove if possible.
> EDIT: This issue may be related to TIKA-2737 and [this comment|https://issues.apache.org/jira/browse/TIKA-539?focusedCommentId=13213524&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13213524].



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