When adding a middleware to a S3Client instance, commands intercepted by the middleware are instances of object, instead of being instances of the original command

[PChol22]

Checkboxes for prior research

• [X] I've gone through Developer Guide and API reference
• [X] I've checked AWS Forums and StackOverflow.
• [X] I've searched for previous similar issues and didn't find any solution.

Describe the bug

When adding a "initialize" middleware to a S3Client instance, commands intercepted by the middleware are instances of object, instead of being instances of the original command.

This is problematic when implementing a cache middleware: 2 different commands (ex: GetPublicAccessBlockCommand and GetBucketLifecycleConfigurationCommand) with the same input (ex: { BucketName: 'abc' }) will be interpreted as the same command when hashed, and one of them will return incoherent data.

This problem doesn't happen in other clients like LambdaClient for example.

SDK version number

@aws-sdk/client-s3@3.474.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

v18.16.1

Reproduction Steps

import {
  GetBucketLifecycleConfigurationCommand,
  S3Client,
} from '@aws-sdk/client-s3';

const s3Client = new S3Client({});
s3Client.middlewareStack.use({
  applyToStack: stack => {
    stack.add(
      next => async args => {
        console.log(args instanceof GetBucketLifecycleConfigurationCommand);

        return next(args);
      },
      { step: 'initialize' },
    );
  },
});

await s3Client.send(
  new GetBucketLifecycleConfigurationCommand({
    Bucket: 'test',
  }),
);
// Will log false <-- This is the problem

Observed Behavior

In the middleware, args is an instance of object, instead of being an instance of GetBucketLifecycleConfigurationCommand.

This broken behaviour happens with every S3Client command I tried, but doesn't happen for any other client (Lambda, EventBridge...)

Expected Behavior

Existing behaviour with clients like LambdaClient:

import {
  GetFunctionConfigurationCommand,
  LambdaClient,
} from '@aws-sdk/client-lambda';

const lambdaClient = new LambdaClient({});
lambdaClient.middlewareStack.use({
  applyToStack: stack => {
    stack.add(
      next => async args => {
        console.log(args instanceof GetFunctionConfigurationCommand);

        return next(args);
      },
      { step: 'initialize' },
    );
  },
});

await lambdaClient.send(
  new GetFunctionConfigurationCommand({
    FunctionName: 'test',
  }),
);
// Will log true

Args of the middleware are an instance of the command that was intercepted

Possible Solution

Dirty temporary workaround for those who are stuck:

Add an extra commandName parameter to the input of commands sent to the S3Client, that helps the middleware know what command it is intercepting

Additional Information/Context

No response

[PChol22]

After some investigation, seems like the usage of next({ ...args }) might be the reason of the issue in files packages/middleware-sdk-s3/src/check-content-length-header.ts and packages/middleware-sdk-s3/src/validate-bucket-name.ts

[kuhe]

The async args => {} part of the middleware has type HandlerArguments e.g. https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/Package/-smithy-types/Interface/InitializeHandlerArguments/.

It does not say args is the type of the input command, only that args.input is the type of the Command's input.

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