Add API Gateway Accept header customization

codegen/aws/core/src/main/java/software/amazon/smithy/python/aws/codegen/customizations/apigateway/ApiGatewayIntegration.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package software.amazon.smithy.python.aws.codegen.customizations.apigateway;
+
+import java.util.List;
+import software.amazon.smithy.codegen.core.Symbol;
+import software.amazon.smithy.codegen.core.SymbolReference;
+import software.amazon.smithy.model.shapes.ShapeId;
+import software.amazon.smithy.python.codegen.CodegenUtils;
+import software.amazon.smithy.python.codegen.GenerationContext;
+import software.amazon.smithy.python.codegen.integrations.PythonIntegration;
+import software.amazon.smithy.python.codegen.integrations.RuntimeClientPlugin;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Adds a runtime plugin that sets the {@code Accept: application/json} header on
+ * Amazon API Gateway requests.
+ */
+@SmithyInternalApi
+public class ApiGatewayIntegration implements PythonIntegration {
+
+    private static final ShapeId API_GATEWAY_SERVICE_ID =
+            ShapeId.from("com.amazonaws.apigateway#BackplaneControlService");
+
+    public static final String ACCEPT_HEADER_PLUGIN = """
+            def accept_header_plugin(config: $1T):
+                config.interceptors.append($2T())
+            """;
+
+    @Override
+    public List<RuntimeClientPlugin> getClientPlugins(GenerationContext context) {
+        if (!context.applicationProtocol().isHttpProtocol()) {
+            return List.of();
+        }
+
+        final String pluginFile = "accept_header";
+        final String moduleName = context.settings().moduleName();
+
+        final SymbolReference acceptHeaderPlugin = SymbolReference.builder()
+                .symbol(Symbol.builder()
+                        .namespace(String.format("%s.%s", moduleName, pluginFile), ".")
+                        .definitionFile(String.format("./src/%s/%s.py", moduleName, pluginFile))
+                        .name("accept_header_plugin")
+                        .build())
+                .build();
+        final SymbolReference acceptHeaderInterceptor = SymbolReference.builder()
+                .symbol(Symbol.builder()
+                        .namespace("smithy_aws_core.interceptors.api_gateway", ".")
+                        .name("ApiGatewayAcceptHeaderInterceptor")
+                        .build())
+                .build();
+
+        return List.of(
+                RuntimeClientPlugin.builder()
+                        .servicePredicate((model, service) -> service.getId().equals(API_GATEWAY_SERVICE_ID))
+                        .pythonPlugin(acceptHeaderPlugin)
+                        .writeAdditionalFiles((c) -> {
+                            String filename = "src/%s/%s.py".formatted(moduleName, pluginFile);
+                            c.writerDelegator()
+                                    .useFileWriter(
+                                            filename,
+                                            moduleName + ".",
+                                            writer -> writer.write(ACCEPT_HEADER_PLUGIN,
+                                                    CodegenUtils.getConfigSymbol(c.settings()),
+                                                    acceptHeaderInterceptor));
+                            return List.of(filename);
+                        })
+                        .build());
+    }
+}

codegen/aws/core/src/main/resources/META-INF/services/software.amazon.smithy.python.codegen.integrations.PythonIntegration

@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0
 #
 
+software.amazon.smithy.python.aws.codegen.customizations.apigateway.ApiGatewayIntegration
 software.amazon.smithy.python.aws.codegen.AwsAuthIntegration
 software.amazon.smithy.python.aws.codegen.AwsProtocolsIntegration
 software.amazon.smithy.python.aws.codegen.AwsServiceIdIntegration

packages/smithy-aws-core/.changes/next-release/smithy-aws-core-feature-148458776e344af993a25112d28b8342.json

@@ -0,0 +1,4 @@
+{
+  "type": "feature",
+  "description": "Add an Amazon API Gateway customization that sets the `Accept: application/json` request header."
+}

packages/smithy-aws-core/src/smithy_aws_core/interceptors/api_gateway.py

@@ -0,0 +1,18 @@
+#  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#  SPDX-License-Identifier: Apache-2.0
+from typing import Any
+
+from smithy_core.interceptors import Interceptor, RequestContext
+from smithy_http import Field
+from smithy_http.aio.interfaces import HTTPRequest
+
+
+class ApiGatewayAcceptHeaderInterceptor(Interceptor[Any, Any, HTTPRequest, None]):
+    """Sets the Accept header to application/json on API Gateway requests."""
+
+    def modify_before_signing(
+        self, context: RequestContext[Any, HTTPRequest]
+    ) -> HTTPRequest:
+        request = context.transport_request
+        request.fields.set_field(Field(name="Accept", values=["application/json"]))
+        return request

packages/smithy-aws-core/tests/unit/interceptors/test_api_gateway.py

@@ -0,0 +1,41 @@
+#  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#  SPDX-License-Identifier: Apache-2.0
+
+from unittest.mock import Mock
+
+from smithy_aws_core.interceptors.api_gateway import ApiGatewayAcceptHeaderInterceptor
+from smithy_core import URI
+from smithy_core.interceptors import RequestContext
+from smithy_core.types import TypedProperties
+from smithy_http import Field, Fields
+from smithy_http.aio import HTTPRequest
+
+
+def _request(fields: Fields) -> HTTPRequest:
+    destination = URI(host="apigateway.us-east-1.amazonaws.com", path="/restapis")
+    return HTTPRequest(destination=destination, method="GET", fields=fields)
+
+
+def test_sets_accept_header() -> None:
+    interceptor = ApiGatewayAcceptHeaderInterceptor()
+    request = _request(Fields())
+    context = RequestContext(
+        request=Mock(), properties=TypedProperties(), transport_request=request
+    )
+
+    result = interceptor.modify_before_signing(context)
+
+    assert result.fields["Accept"].values == ["application/json"]
+
+
+def test_overwrites_existing_accept_header() -> None:
+    interceptor = ApiGatewayAcceptHeaderInterceptor()
+    fields = Fields([Field(name="Accept", values=["application/hal+json"])])
+    request = _request(fields)
+    context = RequestContext(
+        request=Mock(), properties=TypedProperties(), transport_request=request
+    )
+
+    result = interceptor.modify_before_signing(context)
+
+    assert result.fields["Accept"].values == ["application/json"]