DEMO ALTERNATIVE: use cfg.endpoint_resolver to resolve config.endpoint

gems/aws-sdk-core/lib/aws-sdk-core/plugins/regional_endpoint.rb

@@ -79,6 +79,17 @@ class RegionalEndpoint < Seahorse::Client::Plugin
         resolve_endpoint(cfg)
       end
 
+      DefaultEndpointParameters = Struct.new(
+        :region,
+        :use_dual_stack,
+        :use_fips,
+        :endpoint
+        ) do
+        def method_missing(method_name, *_args)
+          nil
+        end
+      end
+
       def after_initialize(client)
         region = client.config.region
         raise Errors::MissingRegionError if region.nil? || region == ''
@@ -150,16 +161,20 @@ def resolve_endpoint(cfg)
           # that a custom endpoint has NOT been configured by the user
           cfg.override_config(:regional_endpoint, true)
 
-          # preserve legacy (pre EP2) client.config.endpoint still resolves a value
-          # when needed.
-          struct = cfg.instance_variable_get(:@struct)
-          if struct
-            # need a separate proc to get namespace/private access to resolve_legacy_endpoint
-            b = proc { resolve_legacy_endpoint(struct) }
-            struct.define_singleton_method(:endpoint) { @endpoint ||= b.call }
-            nil
+          # preserve legacy (pre EP2) client.config.endpoint
+          if cfg.respond_to?(:endpoint_provider) && (endpoint_provider = cfg.endpoint_provider)
+            params = DefaultEndpointParameters.new
+            params.region = cfg.region
+            params.use_dual_stack = cfg.use_dualstack_endpoint
+            params.use_fips = cfg.use_fips_endpoint
+            begin
+              endpoint = endpoint_provider.resolve_endpoint(params)
+              endpoint.url
+            rescue ArgumentError
+              # fallback to legacy
+              resolve_legacy_endpoint(cfg)
+            end
           else
-            # backup in case internal details of config resolver change
             resolve_legacy_endpoint(cfg)
           end
         end

gems/aws-sdk-core/lib/seahorse/client/plugins/endpoint.rb

@@ -24,10 +24,12 @@ def add_handlers(handlers, config)
         end
 
         def after_initialize(client)
-          # validate endpoint only if user set a custom endpoint
-          return if client.config.respond_to?(:regional_endpoint) && client.config.regional_endpoint
-
           endpoint = client.config.endpoint
+          if endpoint.nil?
+            msg = "missing required option `:endpoint'"
+            raise ArgumentError, msg
+          end
+
           endpoint = URI.parse(endpoint.to_s)
           if URI::HTTPS === endpoint or URI::HTTP === endpoint
             client.config.endpoint = endpoint
@@ -40,11 +42,7 @@ def after_initialize(client)
         class Handler < Client::Handler
 
           def call(context)
-            if !context.config.respond_to?(:regional_endpoint) || # generic
-               !context.config.regional_endpoint || # custom endpoint
-               !context.config.respond_to?(:endpoint_provider) # legacy/pre-ep2/no rules
-              context.http_request.endpoint = URI.parse(context.config.endpoint.to_s)
-            end
+            context.http_request.endpoint = URI.parse(context.config.endpoint.to_s)
             @handler.call(context)
           end
 

gems/aws-sdk-s3/lib/aws-sdk-s3/endpoint_provider.rb

@@ -27,6 +27,9 @@ def resolve_endpoint(parameters)
       use_arn_region = parameters.use_arn_region
       use_s3_express_control_endpoint = parameters.use_s3_express_control_endpoint
       disable_s3_express_session_auth = parameters.disable_s3_express_session_auth
+      require 'byebug'
+      byebug
+
       if Aws::Endpoints::Matchers.set?(region)
         if Aws::Endpoints::Matchers.boolean_equals?(accelerate, true) && Aws::Endpoints::Matchers.boolean_equals?(use_fips, true)
           raise ArgumentError, "Accelerate cannot be used with FIPS"