Error in AWS lambda with python when testing through API Gateway

Question

I have a basic lambda function which accepts a JSON, and transforms to XML and uploads the same to s3 bucket. I am running the test through the lambda console and the xml is getting generated and uploaded to s3 as well. Issue happens when I run the test through API Gateway, and there I get the error:

"message": "Internal server error" and Status: 502. The error also points out where is the code issue:
{"errorMessage": "'header'", "errorType": "KeyError", "stackTrace": ["  File \"/var/task/sample.py\", line 21, in printMessage\n    b1.text = event['header']['echoToken']\n"]}

The same code is working when running through lambda console. Below is the code snippet with the line that throws the error:

def printMessage(event, context):
    print(event)
    #event = json.loads(event['header'])
    root = ET.Element("Reservation")
    m1 = ET.Element("header")
    root.append(m1)
    b1 = ET.SubElement(m1, "echoToken")
    b1.text = event['header']['echoToken'] #this line throws error

I got a similar question here: AWS Lambda-API gateway "message": "Internal server error" (502 Bad Gateway). Below is the print of event object.

{'header': {'echoToken': '907f44fc-6b51-4237-8018-8a840fd87f04', 'timestamp': '2018-03-07 20:59:575Z'}, 'reservation': {'hotel': {'uuid': '3_c5f3c903-c43d-4967-88d1-79ae81d00fcb', 'code': 'TASK1', 'offset': '+06:00'}, 'reservationId': 12345, 'confirmationNumbers': [{'confirmationNumber': '12345', 'source': 'ENCORA', 'guest': 'Arturo Vargas'}, {'confirmationNumber': '67890', 'source': 'NEARSOFT', 'guest': 'Carlos Hernández'}], 'lastUpdateTimestamp': '2018-03-07 20:59:541Z', 'lastUpdateOperatorId': 'task.user'}}

As per the solution in the link, if I try to do : header = json.loads(event['header']) I get the below error:

"errorMessage": "the JSON object must be str, bytes or bytearray, not dict",

This is a task that I need to complete, and I have tried few things, but is always failing when tested through API Gateway and POSTMAN. So, my question is: I don't want to change my complete code for XML transformation, and is there any way that I load the complete event object in python, so that it works both through lambda console and API gateway?

Thanks in Advance!!

that event object looks doctored, it should be headers not header — anthony sottile
– anthony sottile, Commented May 1, 2021 at 3:38
the JSON that is given to me to work with, has it as header. — Abhinash Jha
– Abhinash Jha, Commented May 1, 2021 at 4:32

dossani · Accepted Answer · 2021-05-01 03:41:52Z

2

The problem is similar to the one discussed here

Below code will fix the line causing the issue.

eventDict = json.loads(event)
b1Text = json.dumps(eventDict['header']['echoToken'])

print(b1Text)

answered May 1, 2021 at 3:41

dossani

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4 Comments

Abhinash Jha Over a year ago

I did try the above options but it gives sn error when i run in lambda console. Below is teh error: "errorMessage": "the JSON object must be str, bytes or bytearray, not dict",

Abhinash Jha Over a year ago

I checked the shared url, and made the changes accordingly. Below is the change I did: eventDict = json.dumps(event) event = json.loads(eventDict) I am using the using the event again , so that I can use it as a dictionary to get the values that I need to create the XML. Again, in AWS lambda the XML is generated fine, and the same is uploaded to S3 bucket, But when I test through API Gateway, it causes the same error :"errorType": "KeyError", "stackTrace": [" File \"/var/task/sample.py\", line 26, in printMessage\n b1.text = event['header']['echoToken']

Abhinash Jha Over a year ago

I am passing my JSON in the request body section in AWS Gateway.

Abhinash Jha Over a year ago

the answer put me in right direction. marking as right. thanks

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