fix(middleware-flexible-checksums): skip checksum computation if provided

[trivikr]

Issue

Fixes #6744

Description

Skips checksum computation if user provided one in the call

Testing

Test code for printing headers

import { S3 } from "../aws-sdk-js-v3/clients/client-s3/dist-cjs/index.js";
import { NodeHttpHandler } from "../aws-sdk-js-v3/node_modules/@smithy/node-http-handler/dist-cjs/index.js";

// Prints checksum headers for request and response.
class CustomHandler extends NodeHttpHandler {
  constructor() {
    super();
  }

  printChecksumHeaders(prefix, headers) {
    for (const [header, value] of Object.entries(headers)) {
      if (
        header.startsWith("x-amz-checksum-") ||
        header.startsWith("x-amz-sdk-checksum-")
      ) {
        console.log(`${prefix}['${header}']: '${value}'`);
      }
    }
  }

  async handle(request, options) {
    this.printChecksumHeaders("request", request.headers);
    const response = await super.handle(request, options);
    this.printChecksumHeaders("response", response.response.headers);
    return response;
  }
}

const client = new S3({ requestHandler: new CustomHandler() });

Passes user provided checksum value in header

const Bucket = "test-flexible-checksums"; // Replace with your test bucket name.
const Body = "Hello world";
const Key = "helloworld.txt";
const ChecksumCRC32 = "i9aeUg==";

await client.putObject({ Bucket, Key, Body, ChecksumCRC32 });

request['x-amz-checksum-crc32']: 'i9aeUg=='
response['x-amz-checksum-crc32']: 'i9aeUg=='
response['x-amz-checksum-type']: 'FULL_OBJECT'

Passes user provided checksum in header

const Bucket = "test-flexible-checksums"; // Replace with your test bucket name.
const Body = "Hello world";
const Key = "helloworld.txt";
const ChecksumAlgorithm = "CRC32";
const ChecksumCRC32 = "i9aeUg==";

await client.putObject({ Bucket, Key, Body, ChecksumAlgorithm, ChecksumCRC32 });

request['x-amz-sdk-checksum-algorithm']: 'CRC32'
request['x-amz-checksum-crc32']: 'i9aeUg=='
response['x-amz-checksum-crc32']: 'i9aeUg=='
response['x-amz-checksum-type']: 'FULL_OBJECT'

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