bug/trim-large-pages: hi_res page trimming keeps the wrong slice when the MediaBox does not start at y=0

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
87/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
python
Área
backend

Línea de trabajo

Lee unstructured_client/_hooks/custom/split_pdf_hook.py, centrándote en SplitPdfHook._trim_large_pages y en cómo ajusta la MediaBox. Añade una prueba unitaria parametrizada que cubra orígenes de MediaBox distintos de cero, como sugiere el issue; las pruebas existentes actualmente simulan esta función. El objetivo es que se conserven los 4000pt superiores en cada origen, sin cambiar el comportamiento existente para las cajas que empiezan en cero.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Describe the bug

With strategy="hi_res" and PDF splitting, SplitPdfHook._trim_large_pages trims any page taller than MAX_PAGE_LENGTH (4000pt) to its top 4000pt. It does that by setting mediabox.top = mediabox.height and then bottom = top - 4000, which assumes the MediaBox starts at y=0. When the MediaBox has a non-zero bottom edge, the window it keeps is shifted down by that offset:

  • MediaBox [0, 1000, 612, 6000] becomes [0, 1000, 612, 5000]: the top 1000pt of the page are dropped and the bottom part is kept instead.
  • MediaBox [0, 5000, 612, 10000] becomes [0, 1000, 612, 5000], which doesn't overlap the page at all, so that chunk goes to the API as a blank page.

To Reproduce

On main (c1b153f, unstructured-client 0.47.0, pypdf 6.21.4):

import io, sys
from pypdf import PdfReader, PdfWriter
from pypdf.generic import RectangleObject
from unstructured_client._hooks.custom.split_pdf_hook import SplitPdfHook, MAX_PAGE_LENGTH

origin = float(sys.argv[1]) if len(sys.argv) > 1 else 1000.0
w = PdfWriter()
page = w.add_blank_page(width=612, height=5000)
page.mediabox = RectangleObject([0, origin, 612, origin + 5000])  # 5000pt tall, bottom edge at y=origin
buf = io.BytesIO(); w.write(buf); buf.seek(0)

before = PdfReader(buf).pages[0].mediabox
after = SplitPdfHook()._trim_large_pages(PdfReader(buf), {"strategy": "hi_res"}).pages[0].mediabox
print("original:", [float(x) for x in before])
print("trimmed: ", [float(x) for x in after])
print("expected:", [0.0, float(before.top) - MAX_PAGE_LENGTH, 612.0, float(before.top)])

origin 0     trimmed [0, 1000, 612, 5000]   expected [0, 1000, 612, 5000]
origin 1000  trimmed [0, 1000, 612, 5000]   expected [0, 2000, 612, 6000]
origin 5000  trimmed [0, 1000, 612, 5000]   expected [0, 6000, 612, 10000]

Expected behavior

Keep the top 4000pt of the page wherever the MediaBox sits. Dropping the top assignment and only moving the bottom edge does that:

if page.mediabox.height >= max_page_length:
    page.mediabox.bottom = page.mediabox.top - max_page_length

With that change all three cases above match the expected box, and it is the same result as today for MediaBoxes that start at 0. _trim_large_pages has no direct test right now (the unit tests patch it out); I'd suggest a parametrized one over the MediaBox origin like the script above.

Additional context

This only runs when the hook actually splits (hi_res, more pages than one split or a page range). I found it reading the hook, not from a customer file, so I don't know how common offset MediaBoxes are in practice; they do show up in cropped or imposed PDFs. I saw CONTRIBUTING asks for issues rather than PRs, so filing it here.

Lenguaje dominante
Python
Estrellas
120
Forks
22
Merge medio
2 d 3 h
PR fusionados (30 d)
6

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