[Bug]: Flood of "Recursion depth exceeded in _find_image_xrefs_page" #1321
Comments
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On page 18 /Xi9 appears to be in a circular reference loop that includes itself over and over. I can guard against it but the file is likely malformed at this location. Try Ghostscript to rewrite the PDF. If it does just happen to be really deep Python has a system call to increase recursion depth which you could use to force the file through. Doubt it would help though. |
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Thanks, for my test document, Ghostscript detected the problem and repaired the file. |
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I added a guard that should prevent recursion into previously visited XObjects. Please test and let me know if it works. It's still probably best to use ghostscript to repair these files. |
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The guard does not seem to work. If I understand it correctly, you check against all the included/excluded xrefs before the recursion but the xref are added only after the recursion to the set of included/excluded xrefs. Thus, the function can cycle through the circular references forever before the problematic xrefs are added. I tried a different approach by passing all the layers of the recursion: def _find_image_xrefs_container(
pdf: Pdf,
container: Object,
pageno: int,
include_xrefs: MutableSet[Xref],
exclude_xrefs: MutableSet[Xref],
pageno_for_xref: dict[Xref, int],
recursion_layers: tuple[Xref,...] = tuple()
):
"""Find all image XRefs or Form XObject and add to the include/exclude sets."""
if len(recursion_layers) > 10:
log.warning("Recursion depth exceeded in _find_image_xrefs_page")
return
try:
xobjs = container.Resources.XObject
except AttributeError:
return
for _imname, image in dict(xobjs).items():
if image.objgen[1] != 0:
continue # Ignore images in an incremental PDF
xref = Xref(image.objgen[0])
if xref in recursion_layers:
log.warning(f"Skipping {_imname} in page {pageno} since it seems to be recursive.")
continue # Already processed
if Name.Subtype in image and image.Subtype == Name.Form:
# Recurse into Form XObjects
log.debug(f"Recursing into Form XObject {_imname} in page {pageno}")
_find_image_xrefs_container(
pdf,
image,
pageno,
include_xrefs,
exclude_xrefs,
pageno_for_xref,
recursion_layers=tuple([*recursion_layers, xref])
)
continue
if Name.SMask in image:
# Ignore soft masks
smask_xref = Xref(image.SMask.objgen[0])
exclude_xrefs.add(smask_xref)
log.debug(f"xref {smask_xref}: skipping image because it is an SMask")
include_xrefs.add(xref)
log.debug(f"xref {xref}: treating as an optimization candidate")
if xref not in pageno_for_xref:
pageno_for_xref[xref] = pagenoThis seems to work with our problematic PDFs. |
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@jbarlow83: We found a PDF that could not even be processed with the changes posted above. The new (and so far working) version is this: def _find_image_xrefs_container(
pdf: Pdf,
container: Object,
pageno: int,
include_xrefs: MutableSet[ocrmypdf.optimize.Xref],
exclude_xrefs: MutableSet[ocrmypdf.optimize.Xref],
pageno_for_xref: dict[ocrmypdf.optimize.Xref, int],
depth: int = 0,
already_processed_xrefs: typing.Optional[MutableSet[ocrmypdf.optimize.Xref]] = None,
strange_xrefs: typing.Optional[MutableSet[ocrmypdf.optimize.Xref]] = None,
):
"""Find all image XRefs or Form XObject and add to the include/exclude sets."""
if depth > 10:
ocrmypdf.optimize.log.warning(
"Recursion depth exceeded in _find_image_xrefs_page"
)
return
try:
xobjs = container.Resources.XObject
except AttributeError:
return
# If no xrefs were passed, an empty set is created.
_already_processed_xrefs: MutableSet[ocrmypdf.optimize.Xref]
if already_processed_xrefs is None:
_already_processed_xrefs = set()
else:
_already_processed_xrefs = already_processed_xrefs
# If no strange xrefs were passed, an empty set is created.
_strange_xrefs: MutableSet[ocrmypdf.optimize.Xref]
if strange_xrefs is None:
_strange_xrefs = set()
else:
_strange_xrefs = strange_xrefs
# This is a mapping of objects' xrefs to the objects' names and objects themself.
to_be_processed_objects = {
ocrmypdf.optimize.Xref(image.objgen[0]): (_imname, image)
for _imname, image in dict(xobjs).items()
}
# Only the xrefs of the to-be-processed objects.
to_be_processed_xrefs: set[ocrmypdf.optimize.Xref] = set(
to_be_processed_objects.keys()
)
# These are the xrefs that have not been processed before.
unprocessed_xrefs = to_be_processed_xrefs - _already_processed_xrefs
# Collecting "strange" xrefs (probably involved in cyclic xrefs?) for later logging.
_strange_xrefs |= to_be_processed_xrefs - unprocessed_xrefs
# This will be passed to further function calls. Thus, we can consider
# these xrefs processed.
to_be_already_processed_xrefs: set[ocrmypdf.optimize.Xref] = (
set(_already_processed_xrefs) | unprocessed_xrefs
)
for xref in unprocessed_xrefs:
_imname, image = to_be_processed_objects[xref]
if image.objgen[1] != 0:
continue # Ignore images in an incremental PDF
if Name.Subtype in image and image.Subtype == Name.Form:
# Recurse into Form XObjects
ocrmypdf.optimize.log.debug(
f"Recursing into Form XObject {_imname} in page {pageno}"
)
_find_image_xrefs_container(
pdf=pdf,
container=image,
pageno=pageno,
include_xrefs=include_xrefs,
exclude_xrefs=exclude_xrefs,
pageno_for_xref=pageno_for_xref,
depth=depth + 1,
already_processed_xrefs=to_be_already_processed_xrefs,
strange_xrefs=_strange_xrefs,
)
continue
if Name.SMask in image:
# Ignore soft masks
smask_xref = ocrmypdf.optimize.Xref(image.SMask.objgen[0])
exclude_xrefs.add(smask_xref)
ocrmypdf.optimize.log.debug(
f"xref {smask_xref}: skipping image because it is an SMask"
)
# Everything that passed the previous filters is relevant for optimization.
include_xrefs.add(xref)
ocrmypdf.optimize.log.debug(
f"xref {xref}: treating as an optimization candidate"
)
if xref not in pageno_for_xref:
pageno_for_xref[xref] = pageno
# Notifying about strange xrefs.
if depth == 0 and _strange_xrefs:
ocrmypdf.optimize.log.warning(
f"{len(_strange_xrefs)} xrefs on page {pageno} were found to be kind of strange."
)As it turns out, finding suitable variable names is even harder when writing recursive functions. :) |
Describe the bug
I am trying to OCR a lot of documents. Some of them lead to a flood of "Recursion depth exceeded in _find_image_xrefs_page" warnings (>1M warnings per document!). If I understand the problem correctly, this happens when OCRmyPDF tries to optimize embedded images. It seems that these documents contain a deep (and broad) structure of xrefs. The scanning takes verly long and stalls further processing.
Unfortunately, I cannot share the documents for legal reasons.
Is there any way to identify documents that might lead to this problem before running the optimization?
Steps to reproduce
Files
No response
How did you download and install the software?
PyPI (pip, poetry, pipx, etc.)
OCRmyPDF version
16.0.3
Relevant log output
The text was updated successfully, but these errors were encountered: