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ResourceWarning after uploading large files #1242

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perrinjerome opened this issue Jan 4, 2025 · 0 comments · Fixed by #1243
Closed

ResourceWarning after uploading large files #1242

perrinjerome opened this issue Jan 4, 2025 · 0 comments · Fixed by #1243

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@perrinjerome
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What I did:

Upload a file with an html like this that one:

<html>
    <form action="/" method="post" enctype="multipart/form-data">
        <input type="file" id="f" name="f">
        <button type="submit">Upload</button>
    </form>
</html>

What I expect to happen:

no warning

What actually happened:

warning on the console:

./Zope/src/ZPublisher/HTTPRequest.py:195: ResourceWarning: unclosed file <_io.BufferedRandom name=18>
  self.form.clear()
ResourceWarning: Enable tracemalloc to get the object allocation traceback

Very small files do not cause this warning, because a BytesIO is used

What version of Python and Zope/Addons I am using:

This happens on current Zope master branch.

Suggested fix

Multipart documentation recommends closing MultipartPart at the end of request, quoting https://multipart.readthedocs.io/en/latest/usage.html#streaming-parser

Do not forget to close all parts after use to free up resources and avoid ResourceWarnings. Framework developers may want to add logic that automatically frees up resources after the request ended.

Zope request does not keep a reference to the MultipartPart, but creates a FormField

Zope/src/ZPublisher/HTTPRequest.py

Lines 1497 to 1501 in 7802542

field = FormField(
name=part.name,
file=part.file,
filename=part.filename,
headers=part.headers)

which later becomes a FileUpload

Zope/src/ZPublisher/HTTPRequest.py

Lines 547 to 550 in 7802542

if hasattr(item, 'file') and \
hasattr(item, 'filename') and \
hasattr(item, 'headers'):
item = FileUpload(item, self.charset)

so calling MultipartPart.close is not directly applicable, but since what this method does ( code for reference ) is just calling close on the underlying file, calling close on the FileUpload is equivalent.

The fix I'm suggesting is to call close on all FileUploads during HTTPRequest.clear ( I'm sending a pull request doing this ).
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HTTPRequest: close file uploads to prevent ResourceWarning zopefoundation/Zope
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@perrinjerome