SchemaJSRenderer renders invalid Javascript (#5607)

* SchemaJSRenderer renders invalid Javascript

Under Py3 the base64.b64encode() method returns a binary object, which gets rendered as `b'...'` in schema.js. This results in the output becoming:

    var coreJSON = window.atob('b'eyJf...'');

which is invalid Javascript. Because base64 only uses ASCII characters it is safe to decode('ascii') it. Under Py2 this will result in a unicode object, which is fine. Under Py3 it results in a string, which is also fine. This solves the problem and results in a working schema.js output.

* Add regression test for #5608

* Add regression test for #5608

* Apparently the linter on Travis wants the imports in a different order than on my box...

rest_framework/renderers.py

@@ -852,7 +852,7 @@ class SchemaJSRenderer(BaseRenderer):
 
     def render(self, data, accepted_media_type=None, renderer_context=None):
         codec = coreapi.codecs.CoreJSONCodec()
-        schema = base64.b64encode(codec.encode(data))
+        schema = base64.b64encode(codec.encode(data)).decode('ascii')
 
         template = loader.get_template(self.template)
         context = {'schema': mark_safe(schema)}

tests/test_renderers.py

@@ -18,7 +18,7 @@ import coreapi
 from rest_framework import permissions, serializers, status
 from rest_framework.renderers import (
     AdminRenderer, BaseRenderer, BrowsableAPIRenderer, DocumentationRenderer,
-    HTMLFormRenderer, JSONRenderer, StaticHTMLRenderer
+    HTMLFormRenderer, JSONRenderer, SchemaJSRenderer, StaticHTMLRenderer
 )
 from rest_framework.request import Request
 from rest_framework.response import Response
@@ -736,3 +736,20 @@ class TestDocumentationRenderer(TestCase):
 
         html = renderer.render(document, accepted_media_type="text/html", renderer_context={"request": request})
         assert '<h1>Data Endpoint API</h1>' in html
+
+
+class TestSchemaJSRenderer(TestCase):
+
+    def test_schemajs_output(self):
+        """
+        Test output of the SchemaJS renderer as per #5608. Django 2.0 on Py3 prints binary data as b'xyz' in templates,
+        and the base64 encoding used by SchemaJSRenderer outputs base64 as binary. Test fix.
+        """
+        factory = APIRequestFactory()
+        request = factory.get('/')
+
+        renderer = SchemaJSRenderer()
+
+        output = renderer.render('data', renderer_context={"request": request})
+        assert "'ImRhdGEi'" in output
+        assert "'b'ImRhdGEi''" not in output