Ensure that request bodies are always bytes, not text (fixes #163).

It shouldn't matter whether the request body comes from a file or a
string, or whether it is passed to the Request constructor or assigned
later. It should always be stored internally as bytes.

tests/unit/test_serialize.py

@@ -27,6 +27,42 @@ def test_deserialize_new_json_cassette():
         deserialize(f.read(), jsonserializer)
 
 
+REQBODY_TEMPLATE = u'''\
+interactions:
+- request:
+    body: {req_body}
+    headers:
+      Content-Type: [application/x-www-form-urlencoded]
+      Host: [httpbin.org]
+    method: POST
+    uri: http://httpbin.org/post
+  response:
+    body: {{string: ""}}
+    headers:
+      content-length: ['0']
+      content-type: [application/json]
+    status: {{code: 200, message: OK}}
+'''
+
+
+# A cassette generated under Python 2 stores the request body as a string,
+# but the same cassette generated under Python 3 stores it as "!!binary".
+# Make sure we accept both forms, regardless of whether we're running under
+# Python 2 or 3.
+@pytest.mark.parametrize("req_body, expect", [
+    # Cassette written under Python 2 (pure ASCII body)
+    ('x=5&y=2', b'x=5&y=2'),
+    # Cassette written under Python 3 (pure ASCII body)
+    ('!!binary |\n      eD01Jnk9Mg==', b'x=5&y=2'),
+])
+def test_deserialize_py2py3_yaml_cassette(tmpdir, req_body, expect):
+    cfile = tmpdir.join('test_cassette.yaml')
+    cfile.write(REQBODY_TEMPLATE.format(req_body=req_body))
+    with open(str(cfile)) as f:
+        (requests, responses) = deserialize(f.read(), yamlserializer)
+    assert requests[0].body == expect
+
+
 @mock.patch.object(jsonserializer.json, 'dumps',
                    side_effect=UnicodeDecodeError('utf-8', b'unicode error in serialization',
                                                   0, 10, 'blew up'))