From 0c74c98facc2857d364d2bfbe32efa6ab74d3003 Mon Sep 17 00:00:00 2001
From: Jamie Cockburn <jamiec@extramsp.com>
Date: Tue, 24 Oct 2017 13:55:48 +0100
Subject: [PATCH] Stop JSONBoundField mangling invalid JSON (#5526)

---
 rest_framework/utils/serializer_helpers.py | 11 +++++++----
 tests/test_bound_fields.py                 | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/rest_framework/utils/serializer_helpers.py b/rest_framework/utils/serializer_helpers.py
index fa79b6526..6b662a66c 100644
--- a/rest_framework/utils/serializer_helpers.py
+++ b/rest_framework/utils/serializer_helpers.py
@@ -86,10 +86,13 @@ class BoundField(object):
 class JSONBoundField(BoundField):
     def as_form_field(self):
         value = self.value
-        try:
-            value = json.dumps(self.value, sort_keys=True, indent=4)
-        except (TypeError, ValueError):
-            pass
+        # When HTML form input is used and the input is not valid
+        # value will be a JSONString, rather than a JSON primitive.
+        if not getattr(value, 'is_json_string', False):
+            try:
+                value = json.dumps(self.value, sort_keys=True, indent=4)
+            except (TypeError, ValueError):
+                pass
         return self.__class__(self._field, value, self.errors, self._prefix)
 
 
diff --git a/tests/test_bound_fields.py b/tests/test_bound_fields.py
index ade739d41..e90e65edf 100644
--- a/tests/test_bound_fields.py
+++ b/tests/test_bound_fields.py
@@ -1,3 +1,5 @@
+from django.http import QueryDict
+
 from rest_framework import serializers
 
 
@@ -160,3 +162,15 @@ class TestNestedBoundField:
             )
             rendered_packed = ''.join(rendered.split())
             assert rendered_packed == expected_packed
+
+
+class TestJSONBoundField:
+    def test_as_form_fields(self):
+        class TestSerializer(serializers.Serializer):
+            json_field = serializers.JSONField()
+
+        data = QueryDict(mutable=True)
+        data.update({'json_field': '{"some": ["json"}'})
+        serializer = TestSerializer(data=data)
+        assert serializer.is_valid() is False
+        assert serializer['json_field'].as_form_field().value == '{"some": ["json"}'