Unmarshalling small numbers gives unexpected errors

[leocurrie]

Describe the bug

When unmarshalling very small numbers like 0.0000001 from a DynamoDB table, an unexpected Error is thrown.

Your environment

SDK version number

@aws-sdk/util-dynamodb@3.4.0

Is the issue in the browser/Node.js/ReactNative?

Node.js

Details of the browser/Node.js/ReactNative version

Node.js version v12.20.1

Steps to reproduce

• Start with an object containing javascript Number, e.g. {score: 0.0000001}
• Marshall this object using util-dynamodb, then store in a DynamoDB table using client-dynamodb
• Retrieve the record from the table and umarshall it

Observed behavior

When attempting to unmarshall the record, an Error is thrown with the following message:
UnhandledPromiseRejectionWarning: Error: Value 0.0000001 is outside IEEE 754 Floating-Point Arithmetic. Set options.wrapNumbers to get string value.

Expected behavior

The unmarshalling should complete without error.

Sample code

Hopefully this code illustrates the issue:

import { DynamoDB } from '@aws-sdk/client-dynamodb';
import { marshall, unmarshall } from '@aws-sdk/util-dynamodb';

async function doTest(): Promise<void> {
  const tableName = 'my-table';
  const client = new DynamoDB({ region: 'eu-west-1' });
  const data = {
    Id: 'test-id',
    Timestamp: Date.now(),
    data: { score: 0.0000001 }
  };

  await client.putItem({
    TableName: tableName,
    Item: marshall(data)
  });

  const record = await client.query({
    TableName: tableName,
    KeyConditionExpression: 'Id = :id',
    ExpressionAttributeValues: marshall({
      ':id': 'test-id'
    })
  });

  unmarshall(record.Items[0]);
}

void doTest();

[trivikr]

This happens because DynamoDB stores numbers as strings, and the string numerical value of "0.0000001" is 1e-7:

$ node
Welcome to Node.js v12.20.1.
Type ".help" for more information.
> const numValue = 0.0000001;
undefined
> const strValue = numValue.toString();
undefined
> Number(strValue)
1e-7

Relevant code:

aws-sdk-js-v3/packages/util-dynamodb/src/convertToNative.ts

Lines 57 to 61 in cd50eeb

	} else if (num.toString() !== numString) {
	throw new Error(
	`Value ${numString} is outside IEEE 754 Floating-Point Arithmetic. Set options.wrapNumbers to get string value.`
	);
	}

[trivikr]

I couldn't find any other easy way to detect string values for numbers which are outside IEEE 754 Floating-Point Arithmetic.

A third-party dependency like big.js or decimal.js will increase bundle size.
We would be removing the check for num.toString() !== numString to fix this bug.

[github-actions]

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