API Gateway + Lambda download CSV file - csv

Question

I want to do a csv download link with API Gateway + Lambda.
But there is a problem that lambda always return JSON.stringify. Is there a way to resolve this?
s-function.json
"responses": {
"default": {
"statusCode": "200",
"responseParameters": {
"method.response.header.Content-disposition": "'attachment; filename=testing.csv'"
},
"responseTemplates": {
"text/csv": ""
}
}
}
handler.js
var json2csv = require('json2csv');
module.exports.handler = function(event, context, cb) {
var fields = ['car', 'price', 'color'];
var myCars = [
{
"car": "Audi",
"price": 40000,
"color": "blue"
}, {
"car": "BMW",
"price": 35000,
"color": "black"
}, {
"car": "Porsche",
"price": 60000,
"color": "green"
}
];
var csv = json2csv({ data: myCars, fields: fields });
return cb(null, csv);
};
In the downloaded csv file.
"\"car\",\"price\",\"color\"\n\"Audi\",40000,\"blue\"\n\"BMW\",35000,\"black\"\n\"Porsche\",60000,\"green\""
Updated:
I still trying but thank you at least I have direction.
By the way, I can't find API Gateway doc about $input.body.replaceAll. replaceAll is Java function?
Finally, I resolve this by below code in Api Gateway template.
$input.body.replaceAll("\\""","").replaceAll("""","").replaceAll("\\n","
")
s-function escaped double quotes.
"responseTemplates": {
"text/csv": "$input.body.replaceAll(\"\\\\\"\"\",\"\").replaceAll(\"\"\"\",\"\").replaceAll(\"\\\\n\",\"\n\")"
}
return data:
car,price,color
Audi,40000,blue
BMW,35000,black
Porsche,60000,green
The template final replaceAll is weird. CSV don't recognize \n or \r\n, but I try copy new line in IDE and pass to code. It work and it's magical.

Answer 1

Serverless has changed a bit since you asked this question but if you're using the lambda_proxy method of integration, you can use a handler like:
module.exports.handler = (event, context, callback) => {
const csvRows = [
'1,"blah",123',
'2,"qwe",456'
]
const result = csvRows.reduce((prev, curr) => {
return prev + '\n' + curr
})
callback(null, {
headers: {
'Content-Type': 'text/csv',
'Content-disposition': 'attachment; filename=testing.csv'
},
body: result,
statusCode: 200
})
}
Note: I've used ES6 features so you'll want to use Node 6 or higher to directly copy-paste this example.

Answer 2

If you can't fix it on the Lambda function, you could probably do a replaceAll() in the API Gateway mapping template. I think this could work just to replace the escaped double quotes:
$input.body.replaceAll("\\""","")
Edit: So the swagger would be (if I got the escaping right):
"responses": {
"default": {
"statusCode": "200",
"responseParameters": {
"method.response.header.Content-disposition": "'attachment; filename=testing.csv'"
},
"responseTemplates": {
"text/csv": "$input.body.replaceAll(\"\\\"\"\",\"\")"
}
}
}