JSONField(binary=True) represents using binary strings, which JSONRenderer does not support.

[nikmolnar]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

from rest_framework import serializers

class TestSerializer(serializers.Serializer):
    json = serializers.JSONField()

s = TestSerializer(data={'json': "{broken JSON"})
assert s.is_valid() is False

Expected behavior

Invalid JSON should result in is_valid() returning False.

Actual behavior

is_valid() returns True

Specifying binary=True for the field definition results in the desired behavior for serialization, but causes deserialization to fail on Python 3.

[tomchristie]

Unless you set binary=True the field will check for valid primitives, not a valid binary encoded bytestring.
As currently described, you're passing a valid primitive - a string literal.

What you actually want, as you've noted, is this...

class TestSerializer(serializers.Serializer):
    json = serializers.JSONField(binary=True)

Which then works as expected - is_valid() returns False.
I've tested this in python 3 and I can't see what you mean wrt "causes deserialization to fail" - can reconsider if that aspect gets more details.

[xordoquy]

The tricky point with binary=True is that it isn't a json renderable data because it's a binary string and the json renderer expect unicodes.

I'd point out that the documentation for that field would benefit some clarification:

A field class that validates that the incoming data structure consists of valid JSON primitives. In its alternate binary mode, it will represent and validate JSON-encoded binary strings.

As it stands, I understand that it expects a valid JSON input for non binary mode.

[tomchristie]

It isn't a json renderable data because it's a binary string and the json renderer expect unicodes.

Right - then that's the core issue that we should resolve here.

[tomchristie]

Either that or we should output to unicode by default. (Not strictly correct, but it'd do the trick)

[nikmolnar]

Sorry, I misspoke. It doesn't break the deserialization, it breaks the JSONRenderer, which I see is a separate issue.

So until #4187 is resolved, what is the best way to enforce valid JSON inputs for an API?

[tomchristie]

Well, using a binary json blob as a field isn't a particularly common use case, so poss you should just reconsider if that's what you actually want (ie a nested document of json primitives may be better) but if it really is what you need I'd suggest subclassing JSONField and forcing to_representation to do .decode('utf8') on the result so that you have a custom JSONField that returns Unicode, not bytestrings.