fix(lib-dynamodb): remove unnecessary copying

Author: kuhe

lib/lib-dynamodb/src/baseCommand/DynamoDBDocumentClientCommand.ts

@@ -43,32 +43,25 @@ export abstract class DynamoDBDocumentClientCommand<
     marshallOptions.convertTopLevelContainer = marshallOptions.convertTopLevelContainer ?? true;
     unmarshallOptions.convertWithoutMapWrapper = unmarshallOptions.convertWithoutMapWrapper ?? true;
 
-    this.clientCommand.middlewareStack.add(
+    this.clientCommand.middlewareStack.addRelativeTo(
       (next: InitializeHandler<Input | BaseInput, Output | BaseOutput>, context: HandlerExecutionContext) =>
         async (
           args: InitializeHandlerArguments<Input | BaseInput>
         ): Promise<InitializeHandlerOutput<Output | BaseOutput>> => {
+          setFeature(context, "DDB_MAPPER", "d");
           return next({
             ...args,
-            input: this.getCommandInput(),
+            /**
+             * We overwrite `args.input` at this middleware, but do not
+             * mutate the args object itself, which is initially the Command instance.
+             *
+             * The reason for this is to prevent mutations to the Command instance's inputs
+             * from being carried over if the Command instance is reused in a new
+             * request.
+             */
+            input: marshallInput(args.input, this.inputKeyNodes, marshallOptions),
           });
         },
-      {
-        name: "DocumentInitCopyInput",
-        step: "initialize",
-        priority: "high",
-        override: true,
-      }
-    );
-    this.clientCommand.middlewareStack.addRelativeTo(
-      (next: InitializeHandler<Input | BaseInput, Output | BaseOutput>, context: HandlerExecutionContext) =>
-        async (
-          args: InitializeHandlerArguments<Input | BaseInput>
-        ): Promise<InitializeHandlerOutput<Output | BaseOutput>> => {
-          setFeature(context, "DDB_MAPPER", "d");
-          args.input = marshallInput(args.input, this.inputKeyNodes, marshallOptions);
-          return next(args);
-        },
       {
         name: "DocumentMarshall",
         relation: "before",
@@ -93,46 +86,4 @@ export abstract class DynamoDBDocumentClientCommand<
       }
     );
   }
-
-  /**
-   * For snapshotting the user input as the request starts.
-   * The reason for this is to prevent mutations to the Command instance's inputs
-   * from being carried over if the Command instance is reused in a new
-   * request.
-   */
-  private getCommandInput(): Input | BaseInput {
-    return this.documentClone(this.input);
-  }
-
-  /**
-   * Recursive clone of types applicable to DynamoDBDocument.
-   */
-  private documentClone(it: any): any {
-    if (it === null || it === undefined) {
-      return it;
-    }
-    if (it instanceof Set) {
-      return new Set(it.values());
-    }
-    if (it instanceof Map) {
-      return new Map(it.entries());
-    }
-    if (typeof it === "object") {
-      if (it instanceof NumberValue) {
-        return new NumberValue(it.value);
-      }
-      if (it instanceof Uint8Array) {
-        return new Uint8Array(it);
-      }
-      if (Array.isArray(it)) {
-        return it.map((i) => this.documentClone(i));
-      }
-      const out = {} as any;
-      for (const [key, value] of Object.entries(it)) {
-        out[key] = this.documentClone(value);
-      }
-      return out;
-    }
-    return it;
-  }
 }

lib/lib-dynamodb/src/test/mutability.integ.spec.ts

@@ -88,10 +88,9 @@ describe("DynamoDBDocument command mutability", () => {
     await doc.send(command);
 
     // params should remain what it was set to by the caller,
-    // disregarding middleware modifications and mutations
-    // applied by the marshaller.
+    // disregarding mutations applied by the AttributeValue marshaller.
     expect(params).toEqual({
-      TableName: "test",
+      TableName: "modified-by-middleware",
       FilterExpression: "id = :id",
       ExpressionAttributeValues: {
         ":id": "1",
@@ -184,7 +183,7 @@ describe("DynamoDBDocument command mutability", () => {
     await ddb.send(command);
 
     // for regular clients, middleware modifications to the
-    // args.input object persist beyond the request.
+    // args.input object also persist beyond the request.
     expect(params).toEqual({
       TableName: "modified-by-middleware",
       FilterExpression: "id = :id",
@@ -250,8 +249,6 @@ describe("DynamoDBDocument command mutability", () => {
     params.Bucket = `bucket4`;
     await s3.send(command);
 
-    // for regular clients, middleware modifications to the
-    // args.input object persist beyond the request.
     expect(params).toEqual({
       Bucket: "bucket4",
       ExpectedBucketOwner: "me",