deserialization no longer provides deserialized response

[bizob2828]

Checkboxes for prior research

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

Describe the bug

It looks like in 3.929.0 there was a large refactor(#7485). Registering a middleware in the deserialization step doesn't return the deserialized data any longer.

Regression Issue

• Select this option if this issue appears to be a regression.

SDK version number

@aws-sdk/client-bedrock-runtime@3.929.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

n/a

Reproduction Steps

Register a middleware with step of deserialize with priority of low. Make an InvokeModelCommand of ConverseConverse command call with @aws-sdk/client-bedrock-runtime'.

Observed Behavior

I see the result as the ClientHttp2Stream, not deserialized.

Expected Behavior

In the middleware I expect to see the deserialize body

Possible Solution

No response

Additional Information/Context

It seems like this middleware is getting called after that actually does the deserialization. The priority isn't documented but it seems like if I change my middleware to priority high the result of my middleware and the chain is properly serialized. But it feels like it's defeating the purpose of defining a middleware with a step of deserializeif the deserialization happens in a middleware as well now

[kuhe]

Our deserialization process has always been in a middleware placed in the deserialize step of the middleware stack. The deserialize step is the step in which deserialization happens, not a step purely for post-deserialization effects.

From our readme:

By default, each middleware in the same step has undifferentiated order

This means middleware do not have a guaranteed order when placed in the same step without other ordering controls.

There are three ordering controls for middlewares A and B:

• place A and B in different steps. If one of the steps is at the end of the stack, you can operate on the return side (i.e. after the call to next)
• use the relative middleware option object to declare that A is directly ordered in relation to B.
• use the priority configuration. Relative config is more explicit than priority level, so I recommend relation configuration over priority.

I will add code examples in a follow up comment.

[kuhe]

Code examples for inspecting and emplacing middleware in ordered fashion:

Inspecting middleware (log to console)

import { DynamoDB } from "@aws-sdk/client-dynamodb";

const client = new DynamoDB({});

client.middlewareStack.identifyOnResolve(true);

await client.listTables({});

This console.logs the middleware by name resolved during the request in order, with additional information
containing the middlewares' step, aliases, and/or relations.

[
  'loggerMiddleware - initialize',
  'httpAuthSchemeMiddleware - serialize',
  'endpointV2Middleware - serialize',
  'serializerMiddleware - serialize',
  'contentLengthMiddleware - build',
  'getUserAgentMiddleware - build',
  'hostHeaderMiddleware - build',
  'recursionDetectionMiddleware - build',
  'retryMiddleware - finalizeRequest',
  'httpSigningMiddleware (a.k.a. apiKeyMiddleware,tokenMiddleware,awsAuthMiddleware) - finalizeRequest',
  'deserializerMiddleware - deserialize'
]

Using the inverted order to access deserialization from an "earlier" step

In each middleware, because there is a point at which next(args) is called, anything prior to that is in the request phase and anything after that only happens in the response phase.

This means you can access deserialized data from a step other than serialize, if you do so in the response phase.

import { DynamoDB } from "@aws-sdk/client-dynamodb";

const client = new DynamoDB({});

client.middlewareStack.identifyOnResolve(true);

client.middlewareStack.add(
  (next) => async (args) => {
    // outgoing request phase here - no response available yet.
    const result = await next(args);
    // returning response phase here: deserialized output is accessible.
    console.log(result.output.$metadata.httpStatusCode);
    return result;
  },
  {
    step: "build",
  }
);

await client.listTables({});

Output shows the anonymous middleware was added to the build step:

[
  'loggerMiddleware - initialize',
  'httpAuthSchemeMiddleware - serialize',
  'endpointV2Middleware - serialize',
  'serializerMiddleware - serialize',
  'contentLengthMiddleware - build',
  'anonymous - build',
  'getUserAgentMiddleware - build',
  'hostHeaderMiddleware - build',
  'recursionDetectionMiddleware - build',
  'retryMiddleware - finalizeRequest',
  'httpSigningMiddleware (a.k.a. apiKeyMiddleware,tokenMiddleware,awsAuthMiddleware) - finalizeRequest',
  'deserializerMiddleware - deserialize'
]
200

Configuring explicit relative order (recommended)

For explicit relative ordering, use middlewareStack.addRelativeTo.

import { DynamoDB } from "@aws-sdk/client-dynamodb";

const client = new DynamoDB({});

client.middlewareStack.identifyOnResolve(true);

client.middlewareStack.addRelativeTo(
  (next) => async (args) => {
    const result = await next(args);
    console.log("deserialized output is available:", result.output.$metadata.httpStatusCode);
    return result;
  },
  {
    name: "my-custom-middleware",
    toMiddleware: "deserializerMiddleware",
    relation: "before",
  }
);

await client.listTables({});

Because deserialization is in the response phase, the ordering is inverted from what you may find intuitive.

The output shows that the custom middleware is positioned relatively, and relative middleware are always in the same step as their anchor middleware.

[
  'loggerMiddleware - initialize',
  'httpAuthSchemeMiddleware - serialize',
  'endpointV2Middleware - serialize',
  'serializerMiddleware - serialize',
  'contentLengthMiddleware - build',
  'getUserAgentMiddleware - build',
  'hostHeaderMiddleware - build',
  'recursionDetectionMiddleware - build',
  'retryMiddleware - finalizeRequest',
  'httpSigningMiddleware (a.k.a. apiKeyMiddleware,tokenMiddleware,awsAuthMiddleware) - finalizeRequest',
  'my-custom-middleware - before deserializerMiddleware',
  'deserializerMiddleware - deserialize'
]