Read form-data with AWS python lambda

Question

I want to read the "key" parameter of a http post request but it is not working.

def my_handler(event, context):
    print(event)
    print(event['body'])
    print("key: " + event['key'])

    key = event['query']['key']

    encoded_string = str(key).encode("utf-8")
    # Create the file named for example "42.json" containing the appropriate data
    s3_path =  str(key) + '.json'
    s3 = boto3.resource("s3")
    s3.Bucket(BUCKET_NAME).put_object(Key=s3_path, Body=encoded_string)

    message = {
       'message': 'Created {}!'.format(key)  
    }
    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps(message)
    }

Update: If I use the code below, I can read JSON data in an http post but I still cannot read form-data.

def my_handler(event, context):
    print(event)
    print(event['body'])
   # print("key: " + event['key'])
    print("key  " + json.loads(event['body'])["key"])

    key = json.loads(event['body'])["key"]

    encoded_string = str(key).encode("utf-8")
    # Create the file named for example "42.json" containing the appropriate data
    s3_path =  str(key) + '.json'
    s3 = boto3.resource("s3")
    s3.Bucket(BUCKET_NAME).put_object(Key=s3_path, Body=encoded_string)

    message = {
       'message': 'Created {}!'.format(key)  
    }
    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps(message)
    }

bonafidejed · Accepted Answer · 2020-05-07 13:25:54Z

11

I had trouble with this too. I'm specifically working on an AWS Lambda using python3.7. Took a day, but I figured it out.

This code parses the "multipart/form-data" body into a dict called form_data. There are two notes: (a) This code makes an assumption that the post body and headers are utf-8 encoded; that seems to be particular to the AWS API Gateway, but I didn't do any due diligence to test that this holds for all cases. (b) Because the form could have multiple values for any field, the value for any key is a list. You were asking about retrieving "key" from the form data. If there's a single value for "key" then you'd reference form_data['key'][0].

import cgi
import io

def handler(event, context):
    print(event)
    print(event['body'])

    fp = io.BytesIO(event['body'].encode('utf-8'))
    pdict = cgi.parse_header(event['headers']['Content-Type'])[1]
    if 'boundary' in pdict:
        pdict['boundary'] = pdict['boundary'].encode('utf-8')
    pdict['CONTENT-LENGTH'] = len(event['body'])
    form_data = cgi.parse_multipart(fp, pdict)
    print('form_data=', form_data)

edited May 7, 2020 at 13:25

answered Dec 25, 2019 at 19:42

bonafidejed

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9 Comments

rcx935 Over a year ago

This works, thank you, but you forgot to 'import io'

Lonyui Over a year ago

direct useful !

KnowledgeGainer Over a year ago

It is very useful !

Mohsin Saeed Over a year ago

@bonafidejed how can I read file from form_data variable. open() does not work

bonafidejed Over a year ago

@MohsinSaeed that’s a different question altogether. I recommend posting that separately with the code and the error. If you mention me in a comment on that post I’ll take a look.

|

amittn · Accepted Answer · 2018-09-07 10:28:43Z

0

1. I presume that you are using API Gateway then its worth using Lambda proxy integration which is under your Integration requests on your API Gateway. aws docs

IF you use this setting you don't need any mappings to be done.

edited Sep 7, 2018 at 10:28

answered Sep 7, 2018 at 10:05

amittn

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