Getting json body in aws Lambda via API gateway

There are two different Lambda integrations you can configure in API Gateway:

Lambda non-proxy integration (docs), also called Lambda custom integration Lambda proxy integration (docs)

For Lambda non-proxy integration, you can customise what you are going to pass to Lambda in the payload that you don't need to parse the body, but when you are using Lambda Proxy integration in API Gateway, API Gateway will proxy everything to Lambda in payload like this:

{
    "message": "Hello me!",
    "input": {
        "path": "/test/hello",
        "headers": {
            "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
            "Accept-Encoding": "gzip, deflate, lzma, sdch, br",
            "Accept-Language": "en-US,en;q=0.8",
            "CloudFront-Forwarded-Proto": "https",
            "CloudFront-Is-Desktop-Viewer": "true",
            "CloudFront-Is-Mobile-Viewer": "false",
            "CloudFront-Is-SmartTV-Viewer": "false",
            "CloudFront-Is-Tablet-Viewer": "false",
            "CloudFront-Viewer-Country": "US",
            "Host": "wt6mne2s9k.execute-api.us-west-2.amazonaws.com",
            "Upgrade-Insecure-Requests": "1",
            "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36 OPR/39.0.2256.48",
            "Via": "1.1 fb7cca60f0ecd82ce07790c9c5eef16c.cloudfront.net (CloudFront)",
            "X-Amz-Cf-Id": "nBsWBOrSHMgnaROZJK1wGCZ9PcRcSpq_oSXZNQwQ10OTZL4cimZo3g==",
            "X-Forwarded-For": "192.168.100.1, 192.168.1.1",
            "X-Forwarded-Port": "443",
            "X-Forwarded-Proto": "https"
        },
        "pathParameters": {"proxy": "hello"},
        "requestContext": {
            "accountId": "123456789012",
            "resourceId": "us4z18",
            "stage": "test",
            "requestId": "41b45ea3-70b5-11e6-b7bd-69b5aaebc7d9",
            "identity": {
                "cognitoIdentityPoolId": "",
                "accountId": "",
                "cognitoIdentityId": "",
                "caller": "",
                "apiKey": "",
                "sourceIp": "192.168.100.1",
                "cognitoAuthenticationType": "",
                "cognitoAuthenticationProvider": "",
                "userArn": "",
                "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36 OPR/39.0.2256.48",
                "user": ""
            },
            "resourcePath": "/{proxy+}",
            "httpMethod": "GET",
            "apiId": "wt6mne2s9k"
        },
        "resource": "/{proxy+}",
        "httpMethod": "GET",
        "queryStringParameters": {"name": "me"},
        "stageVariables": {"stageVarName": "stageVarValue"},
        "body": "{\"foo\":\"bar\"}",
        "isBase64Encoded": false
    }
}

For the example you are referencing, it is not getting the body from the original request. It is constructing the response body back to API Gateway. It should be in this format:

{
    "statusCode": httpStatusCode,
    "headers": { "headerName": "headerValue", ... },
    "body": "...",
    "isBase64Encoded": false
}

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I think there are a few things to understand when working with API Gateway integration with Lambda.

Lambda Integration vs Lambda Proxy Integration

There used to be only Lambda Integration which requires mapping templates. I suppose this is why still seeing many examples using it.

How to pass a querystring or route parameter to AWS Lambda from Amazon API Gateway

As of September 2017, you no longer have to configure mappings to access the request body.

Serverless Architecture on AWS

Lambda Proxy Integration, If you enable it, API Gateway will map every request to JSON and pass it to Lambda as the event object. In the Lambda function you’ll be able to retrieve query string parameters, headers, stage variables, path parameters, request context, and the body from it. Without enabling Lambda Proxy Integration, you’ll have to create a mapping template in the Integration Request section of API Gateway and decide how to map the HTTP request to JSON yourself. And you’d likely have to create an Integration Response mapping if you were to pass information back to the client. Before Lambda Proxy Integration was added, users were forced to map requests and responses manually, which was a source of consternation, especially with more complex mappings.

Words need to navigate the thinking. To get the terminologies straight.

Lambda Proxy Integration = Pass through Simply pass the HTTP request through to lambda.

Lambda Integration = Template transformation Go through a transformation process using the Apache Velocity template and you need to write the template by yourself.

body is escaped string, not JSON

Using Lambda Proxy Integration, the body in the event of lambda is a string escaped with backslash, not a JSON.

"body": "{\"foo\":\"bar\"}" 

If tested in a JSON formatter.

Parse error on line 1:
{\"foo\":\"bar\"}
-^
Expecting 'STRING', '}', got 'undefined'

The document below is about response but it should apply to request.

I received a "malformed Lambda proxy response" error or a 502 status code with Amazon API Gateway. How do I resolve this?

The body field, if you are returning JSON, must be converted to a string or it will cause further problems with the response. You can use JSON.stringify to handle this in Node.js functions; other runtimes will require different solutions, but the concept is the same.

For JavaScript to access it as a JSON object, need to convert it back into JSON object with json.parse in JapaScript, json.dumps in Python.

How To Work with JSON in JavaScript

Strings are useful for transporting but you’ll want to be able to convert them back to a JSON object on the client and/or the server side.

The AWS documentation shows what to do.

if (event.body !== null && event.body !== undefined) {
    let body = JSON.parse(event.body)
    if (body.time) 
        time = body.time;
}
...
var response = {
    statusCode: responseCode,
    headers: {
        "x-custom-header" : "my custom header value"
    },
    body: JSON.stringify(responseBody)
};
console.log("response: " + JSON.stringify(response))
callback(null, response);

---

If you are using a Lambda Proxy Integration, you need to use JSON.parse(event.body) for JavaScript or json.loads(event["body"]) for Python.

The other examples you are looking at are for an AWS Service Lambda Integration (which is different from a Lambda Proxy Integration), where they have constructed the event template themselves.

See https://stackoverflow.com/a/41656022/2800876 for more detail on the structure of the Lambda Proxy Integration

---

I am using lambda with Zappa; I am sending data with POST in json format:

My code for basic_lambda_pure.py is:

import time
import requests
import json
def my_handler(event, context):
    print("Received event: " + json.dumps(event, indent=2))
    print("Log stream name:", context.log_stream_name)
    print("Log group name:",  context.log_group_name)
    print("Request ID:", context.aws_request_id)
    print("Mem. limits(MB):", context.memory_limit_in_mb)
    # Code will execute quickly, so we add a 1 second intentional delay so you can see that in time remaining value.
    print("Time remaining (MS):", context.get_remaining_time_in_millis())

    if event["httpMethod"] == "GET":
        hub_mode = event["queryStringParameters"]["hub.mode"]
        hub_challenge = event["queryStringParameters"]["hub.challenge"]
        hub_verify_token = event["queryStringParameters"]["hub.verify_token"]
        return {'statusCode': '200', 'body': hub_challenge, 'headers': 'Content-Type': 'application/json'}}

    if event["httpMethod"] == "post":
        token = "xxxx"
    params = {
        "access_token": token
    }
    headers = {
        "Content-Type": "application/json"
    }
        _data = {"recipient": {"id": 1459299024159359}}
        _data.update({"message": {"text": "text"}})
        data = json.dumps(_data)
        r = requests.post("https://graph.facebook.com/v2.9/me/messages",params=params, headers=headers, data=data, timeout=2)
        return {'statusCode': '200', 'body': "ok", 'headers': {'Content-Type': 'application/json'}}

I got the next json response:

{
"resource": "/",
"path": "/",
"httpMethod": "POST",
"headers": {
"Accept": "*/*",
"Accept-Encoding": "deflate, gzip",
"CloudFront-Forwarded-Proto": "https",
"CloudFront-Is-Desktop-Viewer": "true",
"CloudFront-Is-Mobile-Viewer": "false",
"CloudFront-Is-SmartTV-Viewer": "false",
"CloudFront-Is-Tablet-Viewer": "false",
"CloudFront-Viewer-Country": "US",
"Content-Type": "application/json",
"Host": "ox53v9d8ug.execute-api.us-east-1.amazonaws.com",
"Via": "1.1 f1836a6a7245cc3f6e190d259a0d9273.cloudfront.net (CloudFront)",
"X-Amz-Cf-Id": "LVcBZU-YqklHty7Ii3NRFOqVXJJEr7xXQdxAtFP46tMewFpJsQlD2Q==",
"X-Amzn-Trace-Id": "Root=1-59ec25c6-1018575e4483a16666d6f5c5",
"X-Forwarded-For": "69.171.225.87, 52.46.17.84",
"X-Forwarded-Port": "443",
"X-Forwarded-Proto": "https",
"X-Hub-Signature": "sha1=10504e2878e56ea6776dfbeae807de263772e9f2"
},
"queryStringParameters": null,
"pathParameters": null,
"stageVariables": null,
"requestContext": {
"path": "/dev",
"accountId": "001513791584",
"resourceId": "i6d2tyihx7",
"stage": "dev",
"requestId": "d58c5804-b6e5-11e7-8761-a9efcf8a8121",
"identity": {
"cognitoIdentityPoolId": null,
"accountId": null,
"cognitoIdentityId": null,
"caller": null,
"apiKey": "",
"sourceIp": "69.171.225.87",
"accessKey": null,
"cognitoAuthenticationType": null,
"cognitoAuthenticationProvider": null,
"userArn": null,
"userAgent": null,
"user": null
},
"resourcePath": "/",
"httpMethod": "POST",
"apiId": "ox53v9d8ug"
},
"body": "eyJvYmplY3QiOiJwYWdlIiwiZW50cnkiOlt7ImlkIjoiMTA3OTk2NDk2NTUxMDM1IiwidGltZSI6MTUwODY0ODM5MDE5NCwibWVzc2FnaW5nIjpbeyJzZW5kZXIiOnsiaWQiOiIxNDAzMDY4MDI5ODExODY1In0sInJlY2lwaWVudCI6eyJpZCI6IjEwNzk5NjQ5NjU1MTAzNSJ9LCJ0aW1lc3RhbXAiOjE1MDg2NDgzODk1NTUsIm1lc3NhZ2UiOnsibWlkIjoibWlkLiRjQUFBNHo5RmFDckJsYzdqVHMxZlFuT1daNXFaQyIsInNlcSI6MTY0MDAsInRleHQiOiJob2xhIn19XX1dfQ==",
"isBase64Encoded": true
}

my data was on body key, but is code64 encoded, How can I know this? I saw the key isBase64Encoded

I copy the value for body key and decode with This tool and "eureka", I get the values.

I hope this help you. :)

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You may have forgotten to define the Content-Type header. For example:

  return {
    statusCode: 200,
    headers: {
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ items }),
  }

---