Add event stream signing after initial http request signing

.changeset/angry-carpets-own.md

@@ -0,0 +1,5 @@
+---
+"@smithy/core": minor
+---
+
+Add event stream signing after initial http request signing if supported.

packages/core/src/middleware-http-signing/httpSigningMiddleware.ts

@@ -1,22 +1,40 @@
 import { HttpRequest } from "@smithy/protocol-http";
 import {
   ErrorHandler,
+  EventStreamPayloadHandler,
   FinalizeHandler,
   FinalizeHandlerArguments,
   FinalizeHandlerOutput,
   FinalizeRequestMiddleware,
   HandlerExecutionContext,
+  MetadataBearer,
   SelectedHttpAuthScheme,
   SMITHY_CONTEXT_KEY,
   SuccessHandler,
 } from "@smithy/types";
 import { getSmithyContext } from "@smithy/util-middleware";
 
+/**
+ * @internal
+ */
+interface HttpSigningMiddlewareConfig {
+  /**
+   * @internal
+   */
+  eventStreamPayloadHandler?: EventStreamPayloadHandler;
+}
+
 /**
  * @internal
  */
 interface HttpSigningMiddlewareSmithyContext extends Record<string, unknown> {
   selectedHttpAuthScheme?: SelectedHttpAuthScheme;
+  /**
+   * @internal
+   */
+  eventStream?: {
+    input?: boolean;
+  };
 }
 
 /**
@@ -26,20 +44,34 @@ interface HttpSigningMiddlewareHandlerExecutionContext extends HandlerExecutionC
   [SMITHY_CONTEXT_KEY]?: HttpSigningMiddlewareSmithyContext;
 }
 
+/**
+ * @internal
+ */
 const defaultErrorHandler: ErrorHandler = (signingProperties) => (error) => {
   throw error;
 };
 
+/**
+ * @internal
+ */
 const defaultSuccessHandler: SuccessHandler = (
   httpResponse: unknown,
   signingProperties: Record<string, unknown>
 ): void => {};
 
+/**
+ * @internal
+ */
+const isEventStreamInputSupported = (
+  smithyContext: HttpSigningMiddlewareSmithyContext,
+  config: HttpSigningMiddlewareConfig
+) => smithyContext?.eventStream?.input && config.eventStreamPayloadHandler;
+
 /**
  * @internal
  */
 export const httpSigningMiddleware = <Input extends object, Output extends object>(
-  config: object
+  config: HttpSigningMiddlewareConfig
 ): FinalizeRequestMiddleware<Input, Output> => (
   next: FinalizeHandler<Input, Output>,
   context: HttpSigningMiddlewareHandlerExecutionContext
@@ -60,7 +92,13 @@ export const httpSigningMiddleware = <Input extends object, Output extends objec
     identity,
     signer,
   } = scheme;
-  const output = await next({
+  // If the input is an event stream and has a handler, use the eventStreamPayloadHandler
+  // right after signing the initial request.
+  const wrappedNext: FinalizeHandler<Input, Output> = isEventStreamInputSupported(smithyContext, config)
+    ? async (args) =>
+        config.eventStreamPayloadHandler!.handle(next as FinalizeHandler<Input, Output & MetadataBearer>, args, context)
+    : next;
+  const output = await wrappedNext({
     ...args,
     request: await signer.sign(args.request, identity, signingProperties),
   }).catch((signer.errorHandler || defaultErrorHandler)(signingProperties));