Acces variable in JSONPath API Gateway Body Mapping

Question

Using AWS's API Gateway I configured an api resource as an AWS proxy to Kinesis' PutRecords action. The API consumers send me a list of events I need to forward those events to a Kinesis stream.

The format in which they send the data to the API gateway look something similar to this. It contains 1 top level element that's of type Array. The object type of each array item is a JSON document:

{
    "events":[
        {
            "time":"2017-01-01T11:43:21",
            "type":"ItemSelected",
            "application":"iOS Build 3654"
        },{
            "time":"2017-01-01:11:55:32",
            "type":"ItemSelected",
            "application":"iOS Build 3654"
        }
    ]
}

What's needed is to break each separate event into a Kinesis record and send it to as a base64Encoded string to Kinesis.

Using a Body Mapping Template I've configured the following.

{
    "StreamName":"MemberApiAuditLog",
    "Records":[
        #foreach($elem in $input.path('$.events')){
        #set($countVal=$foreach.count-1)
            "Data":"$util.base64Encode($input.json('$.events[$countVal]'))",
            "PartitionKey":"$input.path('$.memberid')"
        }
        #end
    ]
}

The problem I'm having is that the Mapping Template doesn't seem to have an issue with this the $countVal variable in this code: '$.events[$countVal]'. It somehow just doesn't recognize the $countVal. If I replace $countVal with 0, it works just fine.

I need to use $input.json(x) because the mapping template doesn't provide a different way to stringify a json object.

Questions:

1. Other than $input.json(x) is there a way to stringify a json object in a Body Mapping Template?
   1. I've tried JSON.stringify(object), but that didn't work.
2. How can I get the code to recognize the value of countVal in that expression? If that can be resolved, the issue will be solved.

Answer 1

I've manage to make the template work, creating a valid json object.

{
    "streamName": "MemberApiAuditLog",
    "Records": [
        #set($inputRoot = $input.path('$.events'))
        #foreach($elem in $inputRoot) {
           #set($json = $input.json("$[$foreach.index]"))
            "Data":"$util.base64Encode($json)",
        #end
    ]
}

It works for me, hope for you too