Cannot pass array to next task in AWS StepFunction - amazon-web-services

Question

Working on an AWS StepFunction that gets an array of dates from a Lambda call, then passes to a Task that should take that array as a parameter to pass into a lambda.
The Get Date Range task works fine and outputs the date array:
{
"rng": [
"2019-05-07",
"2019-05-09"
]
}
...and the array gets passed into the ProcessDateRange task, but I cannot assign the array the range Parameter.
It literally tries to pass this: "$.rng" instead of this:
[
"2019-05-07",
"2019-05-09"
]
Here's the StateMachine:
{
"StartAt": "Try",
"States": {
"Try": {
"Type": "Parallel",
"Branches": [{
"StartAt": "Get Date Range",
"States": {
"Get Date Range": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789:function:get-date-range",
"Parameters": {
"name": "thename",
"date_query": "SELECT date from sch.tbl_dates;",
"database": "the_db"
}
,
"ResultPath": "$.rng",
"TimeoutSeconds": 900,
"Next": "ProcessDateRange"
},
"ProcessDateRange": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789:function:process-date-range",
"Parameters": {
"range": "$.rng"
},
"ResultPath": "$",
"Next": "Exit"
},
"Exit": {
"Type": "Succeed"
}
}
}],
"Catch": [{
"ErrorEquals": ["States.ALL"],
"ResultPath": "$.Error",
"Next": "Failed"
}],
"Next": "Succeeded"
},
"Failed": {
"Type": "Fail",
"Cause": "There was an error. Please review the logs.",
"Error": "error"
},
"Succeeded": {
"Type": "Succeed"
}
}
}

Answer 1

This is because you are using the wrong syntax for Lambda tasks. To specify the input you need to set the InputPath key, for example:
"ProcessDateRange": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789:function:process-date-range",
"InputPath": "$.rng",
"ResultPath": "$",
"Next": "Exit"
},

Answer 2

If you want a parameter to be interpreted as a JSON path instead of a literal string, add ".$" to the end of the parameter name. To modify your example:
"ProcessDateRange": {
"Type": "Task",
"Resource": "arn:aws:lambda:us-east-1:123456789:function:process-date-range",
"Parameters": {
"range.$": "$.rng"
},
"ResultPath": "$",
"Next": "Exit"
},
Relevant docs here: https://docs.aws.amazon.com/step-functions/latest/dg/connectors-parameters.html#connectors-parameters-path