Stop adding Content-Length: 0 to CRT GetObject requests

.changes/next-release/enhancement-s3-98637.json

@@ -0,0 +1,5 @@
+{
+  "type": "enhancement",
+  "category": "crt",
+  "description": "Stop adding a ``Content-Length: 0`` header to GetObject requests made by the CRT transfer client."
+}

awscli/s3transfer/crt.py

@@ -968,16 +968,6 @@ def _convert_to_crt_http_request(self, botocore_http_request):
         if crt_request.headers.get('Content-MD5') is not None:
             crt_request.headers.remove("Content-MD5")
 
-        # In general, the CRT S3 client expects a content length header. It
-        # only expects a missing content length header if the body is not
-        # seekable. However, botocore does not set the content length header
-        # for GetObject API requests and so we set the content length to zero
-        # to meet the CRT S3 client's expectation that the content length
-        # header is set even if there is no body.
-        if crt_request.headers.get('Content-Length') is None:
-            if botocore_http_request.body is None:
-                crt_request.headers.add('Content-Length', "0")
-
         # Botocore sets the Transfer-Encoding header when it cannot determine
         # the content length of the request body (e.g. it's not seekable).
         # However, CRT does not support this header, but it supports

tests/functional/s3transfer/test_crt.py

@@ -1069,7 +1069,7 @@ def test_download(self):
         self._assert_expected_crt_http_request(
             callargs_kwargs["request"],
             expected_http_method='GET',
-            expected_content_length=0,
+            expected_missing_headers=['Content-Length'],
         )
         self._assert_subscribers_called(future)
         with open(self.filename, 'rb') as f:
@@ -1099,7 +1099,7 @@ def test_download_to_seekable_stream(self):
         self._assert_expected_crt_http_request(
             callargs_kwargs["request"],
             expected_http_method='GET',
-            expected_content_length=0,
+            expected_missing_headers=['Content-Length'],
         )
         self._assert_subscribers_called(future)
         with open(self.filename, 'rb') as f:
@@ -1134,7 +1134,7 @@ def test_download_to_nonseekable_stream(self):
         self._assert_expected_crt_http_request(
             callargs_kwargs["request"],
             expected_http_method='GET',
-            expected_content_length=0,
+            expected_missing_headers=['Content-Length'],
         )
         self._assert_subscribers_called(future)
         self.assertEqual(
@@ -1363,6 +1363,8 @@ def test_within_threshold_downloads_in_single_request(
         request_args = download(size, MULTIPART_THRESHOLD)
         assert request_args['type'] == awscrt.s3.S3RequestType.DEFAULT
         assert request_args['operation_name'] == 'GetObject'
+        assert request_args['request'].headers.get('Content-Length') is None
+        assert request_args['request'].body_stream is None
 
     def test_above_threshold_splits_download(self, download):
         request_args = download(MULTIPART_THRESHOLD + 1, MULTIPART_THRESHOLD)

tests/unit/s3transfer/test_crt.py

@@ -154,6 +154,10 @@ def test_download_request(self):
         self.assertEqual(self.expected_path, crt_request.path)
         self.assertEqual(self.expected_host, crt_request.headers.get("host"))
         self.assertIsNone(crt_request.headers.get("Authorization"))
+        # A GET has no body, so it is sent without a Content-Length header,
+        # just as botocore sends it.
+        self.assertIsNone(crt_request.headers.get("Content-Length"))
+        self.assertIsNone(crt_request.body_stream)
 
     def test_delete_request(self):
         callargs = CallArgs(
@@ -170,6 +174,9 @@ def test_delete_request(self):
         self.assertEqual(self.expected_path, crt_request.path)
         self.assertEqual(self.expected_host, crt_request.headers.get("host"))
         self.assertIsNone(crt_request.headers.get("Authorization"))
+        # Botocore sets a zero Content-Length on bodyless non-GET requests.
+        self.assertEqual("0", crt_request.headers.get("Content-Length"))
+        self.assertIsNone(crt_request.body_stream)
 
     def _create_crt_response_error(
         self, status_code, body, operation_name=None, headers=None