Quotation marks syntax for Elastic search multiline script in Appsync resolver - elasticsearch

Question

In elastic search, you can update data in an index using a script in the post request. And you can write multiline script using triple quotation marks like this (in the open search dev console):
POST /item/_update/123
{
"script" : {
"source":
"""
ctx._source.a = params.a;
ctx._source.b = params.b;
ctx._source.c = params.c;
""",
"lang": "painless",
"params" : {
"a" : 3,
"b" : 3,
"c" : 3
}
}
}
However, I want to write the multiline script in the appsync resolver. I am not able to get it to work cos it keeps giving me syntax error. Below is the mapping template example that fails with error.
{
"version":"2017-03-18",
"operation":"POST",
"path":"/item/_update/123
"params":{
"body": {
"script" :
"source": """
ctx._source.a = params.a;
ctx._source.b = params.b;
ctx._source.c = params.c;
""",
"lang": "painless",
"params" : {
"a": $context.arguments.a,
"b": $context.arguments.b,
"c": $context.arguments.c
}
}
}
}
}
The typical error is like this:
{
"data": {
"updateItem": null
},
"errors": [
{
"path": [
"updateItem"
],
"data": null,
"errorType": "MappingTemplate",
"errorInfo": null,
"locations": [
{
"line": 2,
"column": 3,
"sourceName": null
}
],
"message": "Unexpected character (':' (code 58)): was expecting comma to separate Object entries....\n
The problem is mainly about the quotation mark and how to properly write triple quotation mark in appsync resolver such that it translates to the correct format for elastic search API request.
How can we do this?