[aws-custom-resource] response body is unusable

[ashald]

Summary: AWS SDK returns API response body as a buffer that requires special handling. Without it, it's unusable as flatten function decomposes into a group of fields such as Body.0, Body.1, Body.2 etc, byte by byte.

Reproduction Steps

Example in Java:

AwsCustomResource.Builder.create(scope, id)
    .policy(
        AwsCustomResourcePolicy.fromSdkCalls(
            SdkCallsPolicyOptions.builder()
                .resources(ImmutableList.of(keyArn))
                .build()
        )
    )
    .onUpdate(
        AwsSdkCall.builder()
            .service("S3")
            .action("getObject")
            .parameters(ImmutableMap.of(
                "Bucket", bucket,
                "Key", key
            ))
            .physicalResourceId(PhysicalResourceId.of(key + "@" + Clock.systemUTC().millis()))
            .build()
    )
    .build()

CloudWatch logs show following:

{
    "Status": "SUCCESS",
    "Reason": "OK",
    "PhysicalResourceId": "<REDACTED>/vpc-id@1598324720636",
    "StackId": "<REDACTED>",
    "RequestId": "<REDACTED>",
    "LogicalResourceId": "GetVpcId1BE10C8B",
    "NoEcho": false,
    "Data": {
        "apiVersion": null,
        "region": "us-east-1",
        "AcceptRanges": "bytes",
        "ContentLength": 21,
        "ETag": "\"44b69b6234412df3a8fe5e4e7e8b917a\"",
        "ContentType": "application/octet-stream",
        "ServerSideEncryption": "AES256",
        "Body.0": 118,
        "Body.1": 112,
        "Body.2": 99,
        "Body.3": 45,
        "Body.4": 48,
        "Body.5": 49,
        "Body.6": 101,
        "Body.7": 55,
        "Body.8": 102,
        "Body.9": 48,
        "Body.10": 50,
        "Body.11": 57,
        "Body.12": 48,
        "Body.13": 98,
        "Body.14": 49,
        "Body.15": 48,
        "Body.16": 52,
        "Body.17": 48,
        "Body.18": 56,
        "Body.19": 101,
        "Body.20": 99
    }
}

What did you expect to happen?

At the very least, I expected Data object to have a key Body with content being a raw string.
Ideally, it'd be nice if we could attempt JSON-decode it in case response content type is application/json.

What actually happened?

Please see example above where response body is decomposed into a set of fields such as Body.0, Body.1, Body.2 etc, byte by byte.

Environment

• CLI Version : 1.39
• Framework Version: 1.39
• Node.js Version: v12.18.0
• OS : macOS
• Language (Version): Java (8)

Other

While I'm not using the latest version of CDK, the latest source code indicates that the issues is still present: https://github.com/aws/aws-cdk/blob/master/packages/%40aws-cdk/custom-resources/lib/aws-custom-resource/runtime/index.ts#L118-L122

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