Check Headers of S3 Response and Error

[shirady]

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

How can I check the headers of the response - in case of regular response and error response?
In the AWS CLI tool I can see all the response headers using the --debug flag (regardless if it throws and error).

Regression Issue

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

SDK version number

aws-sdk/client-s3: 3.637.0

Which JavaScript Runtime is this issue in?

Node.js

Details of the browser/Node.js/ReactNative version

v20.11.0

Reproduction Steps

An example of error check headers:

1. Create S3 bucket with versioning.
2. Put object.
3. Delete the object.
4. Head/Get the object with version-id (from step 3, which is the delete marker)
   How can we save the headers for validation later?

Note: this is an example, but the question is general.

Observed Behavior

Can't see all the headers on the thrown error.

Expected Behavior

To have the ability to see all the headers as we can in AWS CLI with the debug flag.

Possible Solution

No response

Additional Information/Context

From the docs AWS docs:
If the specified version in the request is a delete marker, the response returns a 405 Method Not Allowed error and the Last-Modified: timestamp response header.

[kuhe]

For a non-error response, to check the headers, use a custom middleware function. One example is here: https://github.com/aws/aws-sdk-js-v3/blob/main/supplemental-docs/CLIENTS.md#logger-logger, and I give an example below.

import { S3 } from "@aws-sdk/client-s3";

const s3 = new S3();

s3.middlewareStack.add(
  (next) => async (args) => {
    const result = await next(args);
    result.output.$metadata.headers = result.response.headers;
    return result;
  }
);

const buckets = await s3.listBuckets();

console.log(buckets.$metadata.headers);

Do you actually need header data that isn't on the mapped response object? The HeadObject operation's response object contains data mapped from the response headers to begin with.

For a server error response, refer to https://github.com/aws/aws-sdk-js-v3/blob/main/supplemental-docs/ERROR_HANDLING.md#handling-service-returned-errors.

[shirady]

@kuhe thank you.

I want to make sure I understand - in case of an error, we can check err.$response.headers, right? (no need for middlewareStack).

I find writing the middlewareStack hard, can you add more explanations or links? (how can I know the structure to refer to? for example: result.output.$metadata.headers = result.response.headers)

[aBurmeseDev]

I want to make sure I understand - in case of an error, we can check err.$response.headers, right? (no need for middlewareStack).

You're correct. For error responses, you can directly access err.$response.headers without needing to use the middlewareStack.

Regarding your question about understanding the structure to refer to when writing middleware, here's link to middleware session in README which provides a clear example and explanation of how to write middleware and access different parts of the request or response data, including headers.

Hope it helps,
John

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