Ignoring body with application/json payload causes HTTP 400

[Yoan Mollard]

1. Create an example view with Django 2.1.4 that does not consume the request's body:

   @csrf_exempt
   def myview(request):
       #print(request.body.decode("utf8"))
       return HttpResponse()
   

2. Now send a a first POST with application/json content type, e.g. with axios:

   axios.post("/myview", {"some": "data"})
   

3. Send new identical POST requests, and observe that they cause HTTP 400 errors:

   [17/Jan/2019 22:27:47] "POST /myview HTTP/1.1" 200 0
   [17/Jan/2019 22:27:48] "{"some":"data"}POST /myview HTTP/1.1" 200 0
   [17/Jan/2019 22:29:44] code 400, message Bad request syntax ('{"some":"data"}')
   [17/Jan/2019 22:29:44] "{"some":"data"}" 400 -
   

The JSON payload of the first request is still buffered somewhere and mess up later requests.

4. Now comment out the print function in the view, and see that consuming the payload has fixed the issue

[Tim Graham]

Please test with Django 2.1.15 as this looks like a duplicate of #30015.