Fix `HTMLFormRenderer` to ensure a valid `datetime-local` format by mgaligniana · Pull Request #9365 · encode/django-rest-framework

mgaligniana · 2024-04-04T19:28:52Z

Description

Hi!

This PR delete everything after the first 3 digits of the miliseconds part of a DateTimeField input at HTMLFormRenderer to avoid break in browsers:

https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/datetime-local#try_it

Please execute ./runtests.py TestDateTimeFieldHTMLFormRender to run the new tests

Fix #5363

mgaligniana · 2024-05-27T15:47:19Z

Hi @auvipy! Following your comment on #5363 (comment) I ask if you could do the review! Thank you!

rest_framework/renderers.py

stale · 2025-04-27T18:31:20Z

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

auvipy

please address the review comment

mgaligniana · 2025-04-28T03:50:36Z

Thanks @auvipy! I'll do it!

mgaligniana · 2025-06-10T13:41:57Z

Just an update here. I'm still active! I'll do as soon as possible

tests/test_renderers.py

mgaligniana · 2025-07-26T13:21:17Z

I finally did it, sorry for the long delay!

Copilot

Pull Request Overview

This PR fixes HTML5 datetime-local input formatting by truncating milliseconds to 3 digits to ensure browser compatibility. The HTML5 datetime-local input type specification only supports up to 3 digits of milliseconds precision, but DRF was potentially outputting more digits which caused browser validation errors.

Modifies the datetime-local field value formatting in HTMLFormRenderer to limit milliseconds to 3 digits
Adds a test case to verify the correct datetime-local input formatting

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
rest_framework/renderers.py	Updates datetime-local field formatting to truncate milliseconds to 3 digits
tests/test_renderers.py	Adds test case to verify datetime-local input formatting with milliseconds

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rest_framework/renderers.py

tests/test_renderers.py

peterthomassen

Thanks. I have two more remarks:

Timezones currently get dropped, but I assume that's fine because this is about datetime-local which "represent[s] a local date and time, with no time-zone offset information".
The transformation assumes that the string format is iso-8601. It doesn't work if I specify, for example, appointment = serializers.DateTimeField(format='%a %d %b %Y, %I:%M%p'). Shouldn't the internal value be used as an input?

mgaligniana · 2025-08-19T19:53:26Z

Thank you Peter!

Not sure if I'm following: do you mean use the datetime value instead of the input.value (string)?

So let me know if you want to fix this in this pull request

peterthomassen · 2025-08-19T20:04:17Z

do you mean use the datetime value instead of the input.value (string)?

Yes, that's what I meant. Sorry for being unclear!

browniebroke · 2025-08-20T12:00:33Z

I tried to use this branch on a Django project with TIME_ZONE="Europe/Paris" and I'm getting a similar error as the original report, bacause the timezone is not Z but +02:00 at the end. While it feels a bit out of scope of what this fix is trying to do, this last suggestion could address it as well?

mgaligniana · 2025-08-20T13:21:47Z

Correct! I'll go for that approach and add one more test for that case Bruno! Thanks!

stale

rest_framework/renderers.py

tests/test_renderers.py

mgaligniana · 2025-08-21T13:43:32Z

@browniebroke and @peterthomassen thank you so much for your quick reviews and guidance! 🙏

It would be nice to add a couple of test cases with some non-naive datetimes, with a timezone specified. Could try with UTC and another timezone where the offset is non-zero

Sure, I'll add a new test with timezone!

I'm not sure. Is it guaranteed that there is always a parent?

Good question. I didn't fully understand what is parent so I'll read more code to be sure and add new cases if needed!

mgaligniana · 2025-10-15T13:26:59Z

Also, the tests have quite some code duplication (I'm not sure if that is a problem).

Yes!! Of course, I can improve that!

mgaligniana · 2025-10-16T01:21:55Z

Also, the tests have quite some code duplication (I'm not sure if that is a problem).

Yes!! Of course, I can improve that!

Tests are prettier now! (I hope so)

tests/test_renderers.py

mgaligniana · 2025-10-20T02:29:27Z

I've also renamed the format to format_ as it is a Python reserved word

mgaligniana · 2025-10-20T03:03:33Z

@peterthomassen I would need your email to add you as Co-authored-by I think (I rebased it to make it only 1 commit)

peterthomassen · 2025-10-20T07:33:52Z

I've also renamed the format to format_ as it is a Python reserved word

What makes you think that? -- I believe it is not. There are also multiple functions in DRF that define variables with that name (you can find some via git grep 'def .*format=').

@peterthomassen I would need your email to add you as Co-authored-by I think (I rebased it to make it only 1 commit)

Thanks, but that's not necessary :-) Anyway, by address is "my first name" at desec dot io.

mgaligniana · 2025-10-20T11:29:36Z

I meant this builtin function: https://docs.python.org/3/library/functions.html#format I realized when editor highlighted to me

peterthomassen

Ah, I understand what you mean. (That's not reserved, but a built-in, which is shadowed when you redeclare it.)

Anyway, looks great to me now!

mgaligniana · 2025-10-20T11:47:11Z

Ahhh correct! Thank you Peter!!!

tests/test_renderers.py

rest_framework/renderers.py

Co-authored-by: Peter Thomassen

ionelmc

@auvipy hello, can you please revert this change and do another drf release? This PR needs more work as it doesn't handle missing or empty defaults. This PR makes rendering fail hard if no defaults are specified for the fields.

ionelmc · 2026-03-24T13:36:26Z

rest_framework/renderers.py

+            except AttributeError:
+                format_ = api_settings.DATETIME_FORMAT
+
+            if format_ is not None:


This seems to allow another type of failure if the format is None.

ionelmc · 2026-03-24T13:38:17Z

rest_framework/renderers.py

        field = field.as_form_field()

-        if style.get('input_type') == 'datetime-local' and isinstance(field.value, str):
-            field.value = field.value.rstrip('Z')


The previous code allowed blank values, the new one doesn't. This makes rendering fail if no defaults are specified.

ionelmc · 2026-03-24T13:39:15Z

tests/test_renderers.py

+            datetime(2024, 12, 24, 0, 55, 30, 345678, tzinfo=ZoneInfo('Asia/Tokyo')),  # +09:00
+            "2024-12-23T09:55:30.345"  # Rendered in -06:00
+        )
+


Tests are missing the case where the value is empty (allowed and working in the previous drf release).

ionelmc · 2026-03-24T13:49:20Z

@auvipy hello, can you please revert this change and do another drf release? This PR needs more work as it doesn't handle missing or empty defaults. This PR makes rendering fail hard if no defaults are specified for the fields.

Ok, nevermind, this would fix it #9928

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Fixed encode#5363 -- HTML5 datetime-local valid format HTMLFormRenderer

d275c59

Co-authored-by: Peter Thomassen

mgaligniana force-pushed the issue-5363 branch from dba1179 to d275c59 Compare October 28, 2025 15:18

browniebroke added 2 commits October 29, 2025 19:38

Add condition to make code cleanable by pyupgrade

03d842c

Merge branch 'main' into issue-5363

8de7110

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browniebroke added this to the 3.17 milestone Oct 29, 2025

browniebroke added the Bug label Oct 29, 2025

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auvipy merged commit 01659c0 into encode:main Oct 30, 2025
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browniebroke changed the title ~~Fixed #5363 -- HTML5 datetime-local valid format HTMLFormRenderer~~ Fix HTMLFormRenderer to ensure a valid datetime-local format Oct 30, 2025

ionelmc reviewed Mar 24, 2026

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