Raise ValueError when anything but map[string]string is used for Thrift

headers

CHANGES.rst

@@ -5,7 +5,8 @@ Changelog
 0.15.2 (unreleased)
 -------------------
 
-- Nothing changed yet.
+- Raise informative and obvious ``ValueError`` when anything
+  but a map[string]string is passed as headers to the ``TChannel.thrift`` method.
 
 
 0.15.1 (2015-08-07)

tchannel/schemes/thrift.py

@@ -21,11 +21,18 @@ def __init__(self, tchannel):
     def __call__(self, request=None, headers=None, timeout=None,
                  retry_on=None, retry_limit=None):
 
-        if headers is None:
+        if not headers:
             headers = {}
 
         # serialize
-        headers = serializer.serialize_headers(headers=headers)
+        try:
+            headers = serializer.serialize_headers(headers=headers)
+        except (AttributeError, TypeError):
+            raise ValueError(
+                'headers must be a map[string]string (a shallow dict'
+                ' where keys and values are strings)'
+            )
+
         body = serializer.serialize_body(call_args=request.call_args)
 
         response = yield self._tchannel.call(

tests/schemes/test_thrift.py

@@ -1141,3 +1141,44 @@ def testString(request, response, proxy):
         yield tchannel.thrift(
             service.testString('no return!?')
         )
+
+
+@pytest.mark.gen_test
+@pytest.mark.callz
+def test_headers_should_be_a_map_of_strings():
+
+    tchannel = TChannel('client')
+
+    with pytest.raises(ValueError):
+        yield tchannel.thrift(
+            request=True,
+            headers={'key': 1},
+        )
+
+    with pytest.raises(ValueError):
+        yield tchannel.thrift(
+            request=True,
+            headers={1: 'value'},
+        )
+
+    with pytest.raises(ValueError):
+        yield tchannel.thrift(
+            request=True,
+            headers=100,
+        )
+
+    with pytest.raises(ValueError):
+        yield tchannel.thrift(
+            request=True,
+            headers={
+                'key': {
+                    'key': 'value',
+                },
+            },
+        )
+
+    with pytest.raises(ValueError):
+        yield tchannel.thrift(
+            request=True,
+            headers=Exception()
+        )