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Magic for xlsx #36

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Mar 30, 2021
Merged

Magic for xlsx #36

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81b7791
add xlsx documents with irregular structure as fixture
fursich Mar 29, 2021
1a82451
seek wider areas for [Content_Types].xml to magicmatch ms xlsx
fursich Mar 29, 2021
1409843
add office documents that have irregular structure as fixture
fursich Mar 29, 2021
4379fe3
seek wider areas for [Content_Types].xml to magicmatch office documents
fursich Mar 29, 2021
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6 changes: 3 additions & 3 deletions data/custom.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@

<magic priority="50">
<match value="PK\003\004" type="string" offset="0">
<match value="[Content_Types].xml" type="string" offset="30">
<match value="[Content_Types].xml" type="string" offset="30:65536">
<match value="word/" type="string" offset="0:4096" />
</match>

Expand All @@ -39,7 +39,7 @@

<magic priority="50">
<match value="PK\003\004" type="string" offset="0">
<match value="[Content_Types].xml" type="string" offset="30">
<match value="[Content_Types].xml" type="string" offset="30:65536">
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@fursich fursich Mar 30, 2021 •
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The composing parts of google-generated office documents seems to have reversed order. Consequently, the larger the file gets, the later magic strings appears in the file - meaning, we have to go searching for longer bytes, and some sort of trade-off would be needed at certain point.

pptx naturally has larger components (even though test fixture is nothing more than a blank slide), so it has to be at least 30:28168 to find out the string (but that'll be not enough for a pptx with a few contents, so tentatively I put 65536 bytes as maximum search range)

Looks like we have two choices here:

  1. to align with mimemagic that searches the string upto ~5000 bytes. In this case we cannot add google-generated pptx fixture, as it naturally fails.

  2. to take bigger range than mimemagic does, so that it can identify (at least) some office files.

I'm assuming the latter might make sense, but please feel free to correct me if I'm wrong.

In any case we might have to rely on other fallback strategies for larger google-generated office files. Probably the question would come down to "to what extent do we want to try hard to find out embedded magic string?" - let me know what you would think.

<match value="ppt/" type="string" offset="0:4096" />
</match>

Expand All @@ -55,7 +55,7 @@

<magic priority="50">
<match value="PK\003\004" type="string" offset="0">
<match value="[Content_Types].xml" type="string" offset="30">
<match value="[Content_Types].xml" type="string" offset="30:65536">
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At least for a blank xlsx file 4096 would be sufficient. I used a common range for the three different format though, so as to make these numbers less cryptic.

<match value="xl/" type="string" offset="0:4096" />
</match>

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6 changes: 3 additions & 3 deletions lib/marcel/tables.rb
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Expand Up @@ -2160,11 +2160,11 @@ module Marcel
['audio/mpeg', [[0, "\377\362"], [0, "\377\363"], [0, "\377\364"], [0, "\377\365"], [0, "\377\366"], [0, "\377\367"], [0, "\377\372"], [0, "\377\373"], [0, "\377\374"], [0, "\377\375"], [0, "\377\377"], [0, 'ID3']]],
['application/pdf', [[0, '%PDF-'], [0, "\357\273\277%PDF-"]]],
['application/msword', [[0..8, "\320\317\021\340\241\261\032\341", [[546, 'jbjb'], [546, 'bjbj']]]]],
['application/vnd.openxmlformats-officedocument.wordprocessingml.document', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..4096, 'word/']]], [30, '_rels/.rels', [[0..4096, 'word/']]]]]]],
['application/vnd.openxmlformats-officedocument.wordprocessingml.document', [[0, "PK\003\004", [[30..65536, '[Content_Types].xml', [[0..4096, 'word/']]], [30, '_rels/.rels', [[0..4096, 'word/']]]]]]],
['application/vnd.ms-powerpoint', [[0..8, "\320\317\021\340\241\261\032\341", [[1152..4096, "P\000o\000w\000e\000r\000P\000o\000i\000n\000t\000 D\000o\000c\000u\000m\000e\000n\000t"]]]]],
['application/vnd.openxmlformats-officedocument.presentationml.presentation', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..4096, 'ppt/']]], [30, '_rels/.rels', [[0..4096, 'ppt/']]]]]]],
['application/vnd.openxmlformats-officedocument.presentationml.presentation', [[0, "PK\003\004", [[30..65536, '[Content_Types].xml', [[0..4096, 'ppt/']]], [30, '_rels/.rels', [[0..4096, 'ppt/']]]]]]],
['application/vnd.ms-excel', [[2080, 'Microsoft Excel 5.0 Worksheet'], [2080, 'Foglio di lavoro Microsoft Exce'], [2114, 'Biff5'], [2121, 'Biff5'], [0..8, "\320\317\021\340\241\261\032\341", [[1152..4096, "W\000o\000r\000k\000b\000o\000o\000k"]]]]],
['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', [[0, "PK\003\004", [[30, '[Content_Types].xml', [[0..4096, 'xl/']]], [30, '_rels/.rels', [[0..4096, 'xl/']]]]]]],
['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', [[0, "PK\003\004", [[30..65536, '[Content_Types].xml', [[0..4096, 'xl/']]], [30, '_rels/.rels', [[0..4096, 'xl/']]]]]]],
['application/x-dbf', [[0, "(?s)^[\\\\002\\\\003\\\\060\\\\061\\\\062\\\\103\\\\143\\\\203\\\\213\\\\313\\\\365\\\\345\\\\373].[\\\\001-\\\\014][\\\\001-\\\\037].{4}(?:.[^\\\\000]|[\\\\101-\\\\377].)(?:[^\\\\000\\\\001].|.[^\\\\000]).{31}(?<=[\\\\000][^\\\\000]{0,10})[A-Z@+]"]]],
['image/x-tga', [[1, "\001\001\000\000", [[8, ".*[\\\\124\\\\122\\\\125\\\\105\\\\126\\\\111\\\\123\\\\111\\\\117\\\\116\\\\055\\\\130\\\\106\\\\111\\\\114\\\\105\\\\056\\\\000]"]]], [1, "\000\002\000\000", [[8, ".*[\\\\124\\\\122\\\\125\\\\105\\\\126\\\\111\\\\123\\\\111\\\\117\\\\116\\\\055\\\\130\\\\106\\\\111\\\\114\\\\105\\\\056\\\\000]"]]], [1, "\000\003\000\000", [[8, ".*[\\\\124\\\\122\\\\125\\\\105\\\\126\\\\111\\\\123\\\\111\\\\117\\\\116\\\\055\\\\130\\\\106\\\\111\\\\114\\\\105\\\\056\\\\000]"]]]]],
['application/x-endnote-refer', [[0..50, '%A ', [[0..1000, "\n%D ", [[0..1000, "\n%T "]]]]]]],
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Binary file added ...penxmlformats-officedocument.presentationml.presentation/converted_from_google_slide.pptx
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Binary file added ...on/vnd.openxmlformats-officedocument.spreadsheetml.sheet/converted_from_google_sheet.xlsx
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Binary file added ...nd.openxmlformats-officedocument.wordprocessingml.document/converted_from_google_doc.docx
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