Return a 400 status code on invalid JSON input

Instead of returning a 500 HTTP status code, return a 400 status code when the
received input is invalid JSON.
Also add a unit test for this case.

Closes-Bug: #1428462
Change-Id: Id02de0a7b8fcbcb07f7ac534519dcdc1cbb04839

wsme/rest/json.py

@@ -12,7 +12,7 @@ from simplegeneric import generic
 from wsme.types import Unset
 import wsme.types
 import wsme.utils
-from wsme.exc import UnknownArgument, InvalidInput
+from wsme.exc import ClientSideError, UnknownArgument, InvalidInput
 
 
 try:
@@ -211,12 +211,15 @@ def datetime_fromjson(datatype, value):
 
 
 def parse(s, datatypes, bodyarg, encoding='utf8'):
-    if hasattr(s, 'read'):
-        jdata = json.load(s)
-    else:
+    jload = json.load
+    if not hasattr(s, 'read'):
         if six.PY3 and isinstance(s, six.binary_type):
             s = s.decode(encoding)
-        jdata = json.loads(s)
+        jload = json.loads
+    try:
+        jdata = jload(s)
+    except ValueError:
+        raise ClientSideError("Request is not in valid JSON format")
     if bodyarg:
         argname = list(datatypes.keys())[0]
         kw = {argname: fromjson(datatypes[argname], jdata)}

wsme/tests/test_restjson.py

@@ -243,6 +243,15 @@ class TestRestJson(wsme.tests.protocol.RestOnlyProtocolTestCase):
         print(r)
         assert json.loads(r.text) == 2
 
+    def test_invalid_json_body(self):
+        r = self.app.post('/argtypes/setint.json', '{"value": 2',
+                          headers={"Content-Type": "application/json"},
+                          expect_errors=True)
+        print(r)
+        assert r.status_int == 400
+        assert json.loads(r.text)['faultstring'] == \
+            "Request is not in valid JSON format"
+
     def test_unknown_arg(self):
         r = self.app.post('/returntypes/getint.json', '{"a": 2}',
                           headers={"Content-Type": "application/json"},