CODEWITHSUNDEEP
javascriptpostaws-lambdahttp-postaxios
Zachary Ferretti
Zachary Ferretti

Reputation: 85

POST Request Not Recognizing Headers

I am trying to make a POST request to an AWS Lambda Python Script I have set up.

I have already heard about solving the issue of Access-Control-Allow-Origin by adding a header to the Response from AWS lambda, that looks like Access-Control-Allow-Origin:*, and I implemented this in the code I was working on for the get request. Then when I begun creating a POST request, I did the same thing, so that the new POST request originally looked like this: 

def post(event, context):
    try:
        return dict(
            statusCode=200,
            headers= {'Access-Control-Allow-Origin': "*"},
            body="test"
        )
    except Exception as ex:
        return dict(
            statusCode=500,
            body=str(ex)
        )

And this works, in Chrome's Network-Tab I see that we pass a post request and there is no issue, and the header is recognized properly, allowing Cross-Origin calls. But this is pretty much just the GET request I have which is already set up and working. So when I update it to be more similar to a POST METHOD and do what I want the problems begin.

So my code, that I want to be performed in the POST request is simple, I should be able to make the request like such, 

def post(event, context):
    try:
        result=str(event.get("inputOne") + event.get("inputTwo"))
        return dict(
            statusCode=200,
            headers= {'Access-Control-Allow-Origin': "*"},
            body=result
        )
    except Exception as ex:
        return dict(
            statusCode=500,
            body=str(ex)
        )

When I test this in the AWS Lambda Management console, my code works, and I get the expected response back in the body.

But then when I try and call the POST endpoint from my React Site, I once again am getting the error: 

Access to XMLHttpRequest at 'THE_POST_URL' from origin     
'http://localhost:XXX' has been blocked by CORS policy: No 'Access-   
Control-Allow-Origin' header is present on the requested resource.

So for some reason, when the body variable is not just a simple string in quotes like "this" <- it fails. I believe this has to do with the Content-Type in the request being of the form application/json;charset=UTF-8 while my request only accepts (as it says in dev-tools) application/json however even when trying to add the headers to accept this format for content-type, I am still getting the same issues.

I am not entirely sure why the header worked on the GET request, but not the POST request, and would appreciate anyone being able to help teach me, thank you!

EDIT: I have also tried adding 'Access-Control-Allow-Methods': "OPTIONS,GET,POST" to the headers of the post response, but this did not work either.

Upvotes: 4

Views: 1243

Answers (1)

Zachary Ferretti
Zachary Ferretti

Reputation: 85

So after reading through the comments on my question, I decided it was worth going and taking a harder look at the way I had my API Gateway, and Lambda service set up on AWS.

I began using the curl utility in order to try and test my post-call from a terminal utility and found that there it was also failing, but I was able to use CloudWatch to debug, the issue and finally get it working.

The problem that I was facing with my curl Request was that I was not properly formatting the JSON input, but even when I was the Lambda was transforming the event improperly, not resulting in a Dict, as expected.

The curl call I was using can be seen:

curl -X POST  https://myURL.execute-api.myREGION.amazonaws.com/stage/yourPOST \
-d '{"inputOne":80000,"inputTwo":85}'

But in order to read that input properly, and then work with it, I had to update my code in the Lambda to reflect parsing the input properly, this updated lambda code can be found here. The event object that you are passing to this lambda is a DICT object, so on the first line, we use JSON.loads to decode the "body" value of the event, into a dict that we store as body. Then to get the value of the two attributes, we use the command body.get("yourKey").

def yourPOST(event, context):

    body=json.loads(event["body"])
    a=body.get("inputOne")
    c=body.get("inputTwo")

After making these changes the call from my React site works without error! If anyone has any questions feel free to comment, I hope this helped!

Upvotes: 1

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