support unmarshall to convert binary attributes

[zshzbh]

Describe the feature

It was first introduced here: #2634 (comment)

unmarshall will also not convert binary attributes properly. The DynamoDB stream will provide a base64 encoded presentation of the binary attribute and unmarshall does not base64-decode the value.

But it would be good to add this feature to support unmarshall to convert binary attributes

Reproduction steps:

1. Put the JS file in lambda.

import { unmarshall } from "@aws-sdk/util-dynamodb"

export const handler =  async (event) => {
  for (const record of event.Records) {
    if (record.dynamodb?.NewImage) {
      const streamItem = record.dynamodb?.NewImage
      const item = unmarshall(streamItem)
      console.log(item)
    }
  }
}

2: Create a test on lambda, put the following json into test -> test event -> event json and test

{
  "Records": [
    {
      "eventID": "1",
      "eventName": "INSERT",
      "eventVersion": "1.0",
      "eventSource": "aws:dynamodb",
      "awsRegion": "us-west-2",
      "dynamodb": {
        "Keys": {
          "Id": {
            "N": "101"
          }
        },
        "NewImage": {
          "Id": {
            "N": "101"
          },
          "Name": {
            "S": "John Doe"
          },
          "BinaryData": {
            "B": "SGVsbG8gV29ybGQ="
          }
        },
        "SequenceNumber": "111",
        "SizeBytes": 26,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
      },
      "eventSourceARN": "arn:aws:dynamodb:us-west-2:123456789012:table/YourTableName/stream/2023-05-11T00:00:00.000"
    },
    {
      "eventID": "2",
      "eventName": "MODIFY",
      "eventVersion": "1.0",
      "eventSource": "aws:dynamodb",
      "awsRegion": "us-west-2",
      "dynamodb": {
        "Keys": {
          "Id": {
            "N": "102"
          }
        },
        "NewImage": {
          "Id": {
            "N": "102"
          },
          "Name": {
            "S": "Jane Smith"
          },
          "BinaryData": {
            "B": "SGVsbG8gQWdhaW4="
          }
        },
        "SequenceNumber": "222",
        "SizeBytes": 28,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
      },
      "eventSourceARN": "arn:aws:dynamodb:us-west-2:123456789012:table/YourTableName/stream/2023-05-11T00:00:00.000"
    }
  ]
}

Use Case

unmarshall will also not convert binary attributes properly. The DynamoDB stream will provide a base64 encoded presentation of the binary attribute and unmarshall does not base64-decode the value.

Proposed Solution

I have provided the workaround

import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { unmarshall } from "@aws-sdk/util-dynamodb";

const dynamoClient = new DynamoDBClient({ region: "us-west-2" });

function customUnmarshall(item) {
  const unmarshalled = unmarshall(item);
  
  for (const [key, value] of Object.entries(unmarshalled)) {
    if (item[key] && item[key].B) {
      // Decode the base64 string to a UTF-8 string
      unmarshalled[key] = Buffer.from(item[key].B, 'base64').toString('utf-8');
    }
  }
  
  return unmarshalled;
}

export const handler = async (event) => {
  for (const record of event.Records) {
    if (record.dynamodb?.NewImage) {
      const streamItem = record.dynamodb.NewImage;
      const item = customUnmarshall(streamItem);
      console.log("Unmarshalled item (including decoded binary attributes):", item);
      
      for (const [key, value] of Object.entries(item)) {
        if (typeof value === 'string' && item[key] && item[key].B) {
          console.log(`Decoded binary attribute ${key}:`, value);
        }
      }
    }
  }
};

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

SDK version used

latest

Environment details (OS name and version, etc.)

lambda prod

[zshzbh]

test case with binary attribute

{
  "Records": [
    {
      "eventID": "1",
      "eventName": "INSERT",
      "eventVersion": "1.0",
      "eventSource": "aws:dynamodb",
      "awsRegion": "us-west-2",
      "dynamodb": {
        "Keys": {
          "Id": {
            "N": "101"
          }
        },
        "NewImage": {
          "Id": {
            "N": "101"
          },
          "Name": {
            "S": "John Doe"
          },
          "BinaryData": {
            "B": "SGVsbG8gV29ybGQ="
          }
        },
        "SequenceNumber": "111",
        "SizeBytes": 26,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
      },
      "eventSourceARN": "arn:aws:dynamodb:us-west-2:123456789012:table/YourTableName/stream/2023-05-11T00:00:00.000"
    },
    {
      "eventID": "2",
      "eventName": "MODIFY",
      "eventVersion": "1.0",
      "eventSource": "aws:dynamodb",
      "awsRegion": "us-west-2",
      "dynamodb": {
        "Keys": {
          "Id": {
            "N": "102"
          }
        },
        "NewImage": {
          "Id": {
            "N": "102"
          },
          "Name": {
            "S": "Jane Smith"
          },
          "BinaryData": {
            "B": "SGVsbG8gQWdhaW4="
          }
        },
        "SequenceNumber": "222",
        "SizeBytes": 28,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
      },
      "eventSourceARN": "arn:aws:dynamodb:us-west-2:123456789012:table/YourTableName/stream/2023-05-11T00:00:00.000"
    }
  ]
}