fix(middleware-apply-body-checksum): fix request copying with clone

.changeset/thick-hats-explode.md

@@ -0,0 +1,5 @@
+---
+"@smithy/middleware-apply-body-checksum": patch
+---
+
+Fix request copying with `HttpRequest.clone()`.

packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.spec.ts

@@ -73,6 +73,27 @@ describe("applyMd5BodyChecksumMiddleware", () => {
       expect(mockHashDigest.mock.calls.length).toBe(0);
       expect(mockEncoder.mock.calls.length).toBe(0);
     });
+
+    it("should clone the request when applying the checksum", async () => {
+      const handler = applyMd5BodyChecksumMiddleware({
+        md5: MockHash,
+        base64Encoder: mockEncoder,
+        // eslint-disable-next-line @typescript-eslint/no-unused-vars
+        streamHasher: async (stream: ExoticStream) => new Uint8Array(5),
+      })(next, {} as any);
+
+      await handler({
+        input: {},
+        request: new HttpRequest({
+          body: body,
+        }),
+      });
+
+      expect(next.mock.calls.length).toBe(1);
+      const { request } = next.mock.calls[0][0];
+      // Assert that non-enumerable properties like the method `clone()` are preserved.
+      expect(request.clone).toBeDefined();
+    });
   }
 
   it("should use the supplied stream hasher to calculate the hash of a streaming body", async () => {

packages/middleware-apply-body-checksum/src/applyMd5BodyChecksumMiddleware.ts

@@ -17,7 +17,7 @@ export const applyMd5BodyChecksumMiddleware =
   (options: Md5BodyChecksumResolvedConfig): BuildMiddleware<any, any> =>
   <Output extends MetadataBearer>(next: BuildHandler<any, Output>): BuildHandler<any, Output> =>
   async (args: BuildHandlerArguments<any>): Promise<BuildHandlerOutput<Output>> => {
-    let { request } = args;
+    const { request } = args;
     if (HttpRequest.isInstance(request)) {
       const { body, headers } = request;
       if (!hasHeader("content-md5", headers)) {
@@ -30,19 +30,18 @@ export const applyMd5BodyChecksumMiddleware =
           digest = options.streamHasher(options.md5, body);
         }
 
-        request = {
-          ...request,
-          headers: {
-            ...headers,
-            "content-md5": options.base64Encoder(await digest),
-          },
+        const cloned = HttpRequest.clone(request);
+        cloned.headers = {
+          ...headers,
+          "content-md5": options.base64Encoder(await digest),
         };
+        return next({
+          ...args,
+          request: cloned,
+        });
       }
     }
-    return next({
-      ...args,
-      request,
-    });
+    return next(args);
   };
 
 export const applyMd5BodyChecksumMiddlewareOptions: BuildHandlerOptions = {