Ensure body is consumed only once

Fixes: #846
Signed-off-by: Mathieu Parent <math.parent@gmail.com>

tests/unit/test_stubs.py

@@ -1,9 +1,12 @@
 import contextlib
+import http.client as httplib
+from io import BytesIO
+from tempfile import NamedTemporaryFile
 from unittest import mock
 
 from pytest import mark
 
-from vcr import mode
+from vcr import mode, use_cassette
 from vcr.cassette import Cassette
 from vcr.stubs import VCRHTTPSConnection
 
@@ -21,3 +24,52 @@ class TestVCRConnection:
             vcr_connection.cassette = Cassette("test", record_mode=mode.ALL)
             vcr_connection.real_connection.connect()
             assert vcr_connection.real_connection.sock is not None
+
+    def test_body_consumed_once_stream(self, tmpdir, httpbin):
+        self._test_body_consumed_once(
+            tmpdir,
+            httpbin,
+            BytesIO(b"1234567890"),
+            BytesIO(b"9876543210"),
+            BytesIO(b"9876543210"),
+        )
+
+    def test_body_consumed_once_iterator(self, tmpdir, httpbin):
+        self._test_body_consumed_once(
+            tmpdir,
+            httpbin,
+            iter([b"1234567890"]),
+            iter([b"9876543210"]),
+            iter([b"9876543210"]),
+        )
+
+    # data2 and data3 should serve the same data, potentially as iterators
+    def _test_body_consumed_once(
+        self,
+        tmpdir,
+        httpbin,
+        data1,
+        data2,
+        data3,
+    ):
+        with NamedTemporaryFile(dir=tmpdir, suffix=".yml") as f:
+            testpath = f.name
+            # NOTE: ``use_cassette`` is not okay with the file existing
+            #       already.  So we using ``.close()`` to not only
+            #       close but also delete the empty file, before we start.
+            f.close()
+            host, port = httpbin.host, httpbin.port
+            match_on = ["method", "uri", "body"]
+            with use_cassette(testpath, match_on=match_on):
+                conn1 = httplib.HTTPConnection(host, port)
+                conn1.request("POST", "/anything", body=data1)
+                conn1.getresponse()
+                conn2 = httplib.HTTPConnection(host, port)
+                conn2.request("POST", "/anything", body=data2)
+                conn2.getresponse()
+            with use_cassette(testpath, match_on=match_on) as cass:
+                conn3 = httplib.HTTPConnection(host, port)
+                conn3.request("POST", "/anything", body=data3)
+                conn3.getresponse()
+            assert cass.play_counts[0] == 0
+            assert cass.play_counts[1] == 1

tests/unit/test_util.py

@@ -0,0 +1,33 @@
+from io import BytesIO, StringIO
+
+import pytest
+
+from vcr import request
+from vcr.util import read_body
+
+
+@pytest.mark.parametrize(
+    "input_, expected_output",
+    [
+        (BytesIO(b"Stream"), b"Stream"),
+        (StringIO("Stream"), b"Stream"),
+        (iter(["StringIter"]), b"StringIter"),
+        (iter(["String", "Iter"]), b"StringIter"),
+        (iter([b"BytesIter"]), b"BytesIter"),
+        (iter([b"Bytes", b"Iter"]), b"BytesIter"),
+        (iter([70, 111, 111]), b"Foo"),
+        (iter([]), b""),
+        ("String", b"String"),
+        (b"Bytes", b"Bytes"),
+    ],
+)
+def test_read_body(input_, expected_output):
+    r = request.Request("POST", "http://host.com/", input_, {})
+    assert read_body(r) == expected_output
+
+
+def test_unsupported_read_body():
+    r = request.Request("POST", "http://host.com/", iter([[]]), {})
+    with pytest.raises(ValueError) as excinfo:
+        assert read_body(r)
+    assert excinfo.value.args == ("Body type <class 'list'> not supported",)