dschmidt opened a new pull request, #3096:
URL: https://github.com/apache/tika/pull/3096
Getting "the thumbnail of this file" out of Tika takes format knowledge on
the client: the THUMBNAIL of a Word or Excel file is an EMF/WMF whose usable
form is the RENDERING underneath it, a PDF has no THUMBNAIL but a page
RENDERING, the THUMBNAIL of a DOCX inside a ZIP is not the ZIP's, and with
rendering enabled the picture of an embedded OLE object is a RENDERING too,
plus the request configuration that switches the renderers on.
`POST`/`PUT /unpack/thumbnail`, next to `/unpack` and `/unpack/all`, answers
with the thumbnail as JSON: the `/rmeta` metadata object of the embedded
document that is the thumbnail and the image as base64, or `204` if the
document has none.
```
{
"metadata": { "Content-Type": "image/png", "tiff:ImageWidth": "800",
"tk:embedded-resource-type": "RENDERING", ... },
"image": "iVBORw0KGgo..."
}
```
It is one forked parse in unpack mode with a fixed parse context: text
extraction off, PDF page 1 rendered at 96 dpi without OCR, EMF/WMF thumbnails
rendered (`renderOnlyEmbeddedResourceTypes: ["THUMBNAIL"]`, from #3095, so the
pictures of embedded objects are not rendered), OCR of images off, only
THUMBNAIL and RENDERING embedded documents extracted, together with their
metadata. `ThumbnailSelector` then picks, in this order, the raster THUMBNAIL
directly below the document, the rendering of a vector THUMBNAIL, or the
RENDERING of the first page. It extracts what the document carries; it does not
resize or convert. A request-supplied parser configuration wins over the fixed
one.
Verified against a server built from main plus the open thumbnail PRs: docx,
xlsx, doc, xls, ppt, pptx, odt, epub, GeoGebra, Pages, Numbers, Keynote, mp3,
m4a, flac, ogg, pdf, nef and pef all answer with the right image; a zip, a
plain jpeg and a doc without a thumbnail answer 204. Raw camera files need
their file name (`Content-Disposition`), as they are detected by extension.
Note: `embedded-limits.maxDepth` is 3 in the fixed context because of the
off-by-one in the depth limit (separate ticket); 2 would be correct once that
is fixed.
https://issues.apache.org/jira/browse/TIKA-4856
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