Fix matching on 'body' failing when Unicode symbols are present in them

Matching on bodies uses urllib.parse.parse_qs(), which fails to handle
UTF-8+URLEncoded POST bodies when the input is `bytes` rather than `str`,
causing matching to fail..
Fixed this by always doing decode('ascii') on URLEncoded POST bodies first.

tests/integration/test_requests.py

@@ -282,3 +282,17 @@ def test_filter_post_params(tmpdir, httpbin_both):
         requests.post(url, data={'key': 'value'})
     with vcr.use_cassette(cass_loc, filter_post_data_parameters=['key']) as cass:
         assert b'key=value' not in cass.requests[0].body
+
+
+def test_post_unicode_match_on_body(tmpdir, httpbin_both):
+    '''Ensure that matching on POST body that contains Unicode characters works.'''
+    data = {'key1': 'value1', '●‿●': '٩(●̮̮̃•̃)۶'}
+    url = httpbin_both + '/post'
+
+    with vcr.use_cassette(str(tmpdir.join('requests.yaml')), additional_matchers=('body',)):
+        req1 = requests.post(url, data).content
+
+    with vcr.use_cassette(str(tmpdir.join('requests.yaml')), additional_matchers=('body',)):
+        req2 = requests.post(url, data).content
+
+    assert req1 == req2

vcr/matchers.py

@@ -56,9 +56,12 @@ def _transform_json(body):
 _xml_header_checker = _header_checker('text/xml')
 _xmlrpc_header_checker = _header_checker('xmlrpc', header='User-Agent')
 _checker_transformer_pairs = (
-    (_header_checker('application/x-www-form-urlencoded'), urllib.parse.parse_qs),
-    (_header_checker('application/json'), _transform_json),
-    (lambda request: _xml_header_checker(request) and _xmlrpc_header_checker(request), xmlrpc_client.loads),
+    (_header_checker('application/x-www-form-urlencoded'),
+        lambda body: urllib.parse.parse_qs(body.decode('ascii'))),
+    (_header_checker('application/json'),
+        _transform_json),
+    (lambda request: _xml_header_checker(request) and _xmlrpc_header_checker(request),
+        xmlrpc_client.loads),
 )