Update event stream tests

botocore/eventstream.py

@@ -466,9 +466,9 @@ def _parse_prelude(self):
         prelude_bytes = self._data[:_PRELUDE_LENGTH]
         raw_prelude, _ = DecodeUtils.unpack_prelude(prelude_bytes)
         prelude = MessagePrelude(*raw_prelude)
-        self._validate_prelude(prelude)
         # The minus 4 removes the prelude crc from the bytes to be checked
         _validate_checksum(prelude_bytes[: _PRELUDE_LENGTH - 4], prelude.crc)
+        self._validate_prelude(prelude)
         return prelude
 
     def _parse_headers(self):

tests/unit/test_eventstream.py

@@ -218,7 +218,7 @@
         b"\x00\x00\x00=\xff\x00\x01\x02\x07\xfd\x83\x96\x0ccontent-type\x07\x00"
         b"\x10application/json{'foo':'bar'}\x8d\x9c\x08\xb1"
     ),
-    InvalidHeadersLength,
+    ChecksumMismatch,
 )
 
 CORRUPTED_HEADERS = (
@@ -231,7 +231,7 @@
 
 CORRUPTED_LENGTH = (
     b"\x01\x00\x00\x1d\x00\x00\x00\x00\xfdR\x8cZ{'foo':'bar'}\xc3e96",
-    InvalidPayloadLength,
+    ChecksumMismatch,
 )
 
 CORRUPTED_PAYLOAD = (
@@ -247,13 +247,40 @@
     DuplicateHeader,
 )
 
+# In contrast to the CORRUPTED_HEADERS case, this message is otherwise
+# well-formed - the checksums match.
+INVALID_HEADERS_LENGTH = (
+    (
+        b"\x00\x00\x00\x3d"  # total length
+        b"\xff\x00\x01\x02"  # headers length
+        b"\x15\x83\xf5\xc2"  # prelude crc
+        b"\x0ccontent-type\x07\x00\x10application/json"  # headers
+        b"{'foo':'bar'}"  # payload
+        b"\x2f\x37\x7f\x5d"  # message crc
+    ),
+    InvalidHeadersLength,
+)
+
+# In contrast to the CORRUPTED_PAYLOAD case, this message is otherwise
+# well-formed - the checksums match.
+INVALID_PAYLOAD_LENGTH = (
+    b"\x01\x00\x00\x11"  # total length
+    + b"\x00\x00\x00\x00"  # headers length
+    + b"\xf4\x08\x61\xc5"  # prelude crc
+    + b"0" * (16 * 1024**2 + 1)  # payload
+    + b"\x2a\xb4\xc5\xa5",  # message crc
+    InvalidPayloadLength,
+)
+
 # Tuples of encoded messages and their expected exception
 NEGATIVE_CASES = [
     CORRUPTED_LENGTH,
     CORRUPTED_PAYLOAD,
     CORRUPTED_HEADERS,
     CORRUPTED_HEADER_LENGTH,
     DUPLICATE_HEADER,
+    INVALID_HEADERS_LENGTH,
+    INVALID_PAYLOAD_LENGTH,
 ]
 
 
@@ -311,7 +338,19 @@ def test_all_positive_cases():
         assert_message_equal(expected, decoded)
 
 
-@pytest.mark.parametrize("encoded, exception", NEGATIVE_CASES)
+@pytest.mark.parametrize(
+    "encoded, exception",
+    NEGATIVE_CASES,
+    ids=[
+        "corrupted-length",
+        "corrupted-payload",
+        "corrupted-headers",
+        "corrupted-headers-length",
+        "duplicate-headers",
+        "invalid-headers-length",
+        "invalid-payload-length",
+    ],
+)
 def test_negative_cases(encoded, exception):
     """Test that all negative cases raise the expected exception."""
     with pytest.raises(exception):