Emit handlers before endpoint resolution

Emit `provide-client-params.*` and
`before-parameter-build.*` before endpoint
resolution.

This ports the following botocore pull request:

boto/botocore#2920

One update to the endpoint name in the
test_signers.py unit test was applied to use the
region name in the s3 endpoint, consistent with
existing CLI v2 tests.

.changes/next-release/bugfix-endpoints-90314.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "endpoints",
+  "description": "\"Include params set in provide-client-param event handlers in dynamic context params for endpoint resolution.\""
+}

awscli/botocore/client.py

@@ -602,7 +602,6 @@ def _resolve_signature_version(self, service_name, resolved):
 
 
 class BaseClient(object):
-
     # This is actually reassigned with the py->op_name mapping
     # when the client creator creates the subclass.  This value is used
     # because calls such as client.get_paginator('list_objects') use the
@@ -682,6 +681,12 @@ def _make_api_call(self, operation_name, api_params):
             'auth_type': operation_model.auth_type,
         }
 
+        api_params = self._emit_api_params(
+            api_params=api_params,
+            operation_model=operation_model,
+            context=request_context,
+        )
+
         (
             endpoint_url,
             additional_headers,
@@ -756,8 +761,6 @@ def _convert_to_request_dict(
             headers=None,
             set_user_agent_header=True,
     ):
-        api_params = self._emit_api_params(
-            api_params, operation_model, context)
         request_dict = self._serializer.serialize_to_request(
             api_params, operation_model)
         if not self._client_config.inject_host_prefix:

awscli/botocore/signers.py

@@ -614,6 +614,11 @@ def generate_presigned_url(self, ClientMethod, Params=None, ExpiresIn=3600,
 
     operation_model = self.meta.service_model.operation_model(
         operation_name)
+    params = self._emit_api_params(
+        api_params=params,
+        operation_model=operation_model,
+        context=context,
+    )
     bucket_is_arn = ArnParser.is_arn(params.get('Bucket', ''))
     (
         endpoint_url,
@@ -738,7 +743,11 @@ def generate_presigned_post(self, Bucket, Key, Fields=None, Conditions=None,
     # serialized to what a presign post requires.
     operation_model = self.meta.service_model.operation_model(
         'CreateBucket')
-    params = {'Bucket': bucket}
+    params = self._emit_api_params(
+        api_params={'Bucket': bucket},
+        operation_model=operation_model,
+        context=context,
+    )
     bucket_is_arn = ArnParser.is_arn(params.get('Bucket', ''))
     (
         endpoint_url,

tests/functional/botocore/test_context_params.py

@@ -330,7 +330,7 @@ def test_client_context_param_sent_to_endpoint_resolver(
         ),
     )
 
-    # Stub client to prevent a request from getting sent and asceertain that
+    # Stub client to prevent a request from getting sent and ascertain that
     # only a single request would get sent. Wrap the EndpointProvider's
     # resolve_endpoint method for inspecting the arguments it gets called with.
     with ClientHTTPStubber(client, strict=True) as http_stubber:
@@ -475,3 +475,37 @@ def test_dynamic_context_param_sent_to_endpoint_resolver(
         )
     else:
         mock_resolve_endpoint.assert_called_once_with(Region='us-east-1')
+
+def test_dynamic_context_param_from_event_handler_sent_to_endpoint_resolver(
+    monkeypatch,
+    patched_session,
+):
+    # patch loader to return fake service model and fake endpoint ruleset
+    patch_load_service_model(
+        patched_session,
+        monkeypatch,
+        FAKE_MODEL_WITH_DYNAMIC_CONTEXT_PARAM,
+        FAKE_RULESET_WITH_DYNAMIC_CONTEXT_PARAM,
+    )
+    # event handler for provide-client-params that modifies the value of the
+    # MockOpParam parameter
+    def change_param(params, **kwargs):
+        params['MockOpParam'] = 'mock-op-param-value-2'
+    client = patched_session.create_client(
+        'otherservice', region_name='us-east-1'
+    )
+    client.meta.events.register_last(
+        'provide-client-params.other-service.*', change_param
+    )
+    with ClientHTTPStubber(client, strict=True) as http_stubber:
+        http_stubber.add_response(status=200)
+        with mock.patch.object(
+            client._ruleset_resolver._provider,
+            'resolve_endpoint',
+            wraps=client._ruleset_resolver._provider.resolve_endpoint,
+        ) as mock_resolve_endpoint:
+            client.mock_operation(MockOpParam='mock-op-param-value-1')
+    mock_resolve_endpoint.assert_called_once_with(
+        Region='us-east-1',
+        FooDynamicContextParamName='mock-op-param-value-2',
+    )

tests/unit/botocore/test_signers.py

@@ -868,6 +868,33 @@ def test_generate_presign_url_emits_is_presign_in_context(self):
                 'the following kwargs emitted: %s' % kwargs
             )
 
+    def test_context_param_from_event_handler_sent_to_endpoint_resolver(self):
+        def change_bucket_param(params, **kwargs):
+            params['Bucket'] = 'mybucket-bar'
+        self.client.meta.events.register_last(
+            'provide-client-params.s3.*', change_bucket_param
+        )
+        self.client.generate_presigned_url(
+            'get_object', Params={'Bucket': 'mybucket-foo', 'Key': self.key}
+        )
+        ref_request_dict = {
+            'body': b'',
+            # If the bucket name set in the provide-client-params event handler
+            # was correctly passed to the endpoint provider as a dynamic context
+            # parameter, it will appear in the URL and the auth_path:
+            'url': 'https://mybucket-bar.s3.us-east-1.amazonaws.com/mykey',
+            'headers': {},
+            'auth_path': '/mybucket-bar/mykey',
+            'query_string': {},
+            'url_path': '/mykey',
+            'method': 'GET',
+            'context': mock.ANY,
+        }
+        self.generate_url_mock.assert_called_with(
+            request_dict=ref_request_dict,
+            expires_in=3600,
+            operation_name='GetObject',
+        )
 
 class TestGeneratePresignedPost(unittest.TestCase):
     def setUp(self):