AWS Lambda Function is misinterpreting event dictionary in python?
Solution 1
- The request is fully packaged and sent as a single string in the
'body'
key of theevent
dict. - This behaviour is different from the test console or invoking from CLI which has only the payload in the
event
dict meaningevent.get('type')
works directly.
Example code showing how to access the value of "type"
key in payload:
import json
def lambda_handler(event, context):
body_str = event.get("body", "{}")
body_str = body_str if body_str else "{}"
body_obj = json.loads(body_str)
a = body_obj.get("type", "")
Solution 2
When you invoke the lambda locally or through the Lambda console, you are invoking that lambda directly and so your lambda receives exactly what you're sending.
When you invoke it through API Gateway, API Gateway creates the event
object for you based on your HTTP request. It adds the HTTP headers, path, query strings, payload, etc.
Here's a summary of what you're getting as an event
from an API Gateway invocation:
{
"resource": "Resource path",
"path": "Path parameter",
"httpMethod": "Incoming request's method name"
"headers": {Incoming request headers}
"queryStringParameters": {query string parameters }
"pathParameters": {path parameters}
"stageVariables": {Applicable stage variables}
"requestContext": {Request context, including authorizer-returned key-value pairs}
"body": "A JSON string of the request payload."
"isBase64Encoded": "A boolean flag to indicate if the applicable request payload is Base64-encode"
}
As you can see, the body
will be sent to you as a string
which you can parse using json.loads()
.
Solution 3
I have a better suggestion to test.
Just return the event that you are receiving in the lambda_handler.
kmcodes
By Day: Running a startup helping make the dream of Digital India a reality. Wear many hats, primarily skilled at creating processes and then seeing how technology can be used to automate/simplify them. At night: Learning how to code, primarily python. Training: Non-practising Electrical Engineer (Power systems) with an MBA in Marketing.
Updated on June 16, 2022Comments
-
kmcodes almost 2 years
I am trying to deploy a google calendar api to AWS Lambda. Since I was facing a problem in extracting the value from the event dictionary (created by lambda from the JSON payload of a POST request), i created a toy function to test
def handler(event,context): a=event.get("type") if a=='create': return { "statusCode": 200, "headers": { "Content-Type": "text/plain"}, #"body": "Event_id"+ str(event_identifier) + " Event Link: " +str(links) "body" : str(a) } else: return { "statusCode": 200, "headers": { "Content-Type": "text/plain"}, #"body": "Event_id"+ str(event_identifier) + " Event Link: " +str(links) "body" : "nope" }
While testing on the Lambda console with the following JSON, I get the correct response.
Test Payload: { "start_time" : "2018-01-24T09:00:00", "end_time" : "2018-01-24T13:00:00", "type": "create", "event_identifier": "pvno", "summary": "Company", "booking-email": "[email protected]" }
Response:
{ "body": "create", "headers": { "Content-Type": "text/plain" }, "statusCode": 200 }
When I send the same payload from postman(binary or body POST) (or test on API gateway console), I get "None" when I return the value from event.get("type").
To explain further, if I try and get the event.get('body') and return it all as a string I get the below, which is incorrect according to how the lambda event should work:
{ "start_time" : "2018-01-24T09:00:00", "end_time" : "2018-01-24T13:00:00", "type": "create", "event_identifier": "pvnoc", "summary": "Company", "booking-email": "[email protected]" }
My questions:
- What am I doing wrong?
- How can I get the correct value from the event dictionary?