How to add metadata while using boto3 create_presigned_post?

Question

Want to add custom metadata to a file that I upload using create_presigned_post from boto3. I am running the following code but am getting 403 response. The code below is borrowed from here. Am I doing something wrong?

def create_presigned_post(bucket_name, object_name,
                          fields=None, conditions=None, expiration=3600):

    # Generate a presigned S3 POST URL
    s3_client = boto3.client('s3')
    try:
        response = s3_client.generate_presigned_post(bucket_name,
                                                     object_name,
                                                     Fields=fields,
                                                     Conditions=conditions,
                                                     ExpiresIn=expiration)
    except ClientError as e:
        print(e)
        return None

    # The response contains the presigned URL and required fields
    return response

# Generate a presigned S3 POST URL
object_name = 'test-file.txt'
response = create_presigned_post('temp', object_name, fields={'x-amz-meta-test_key': 'test_val'})

# Demonstrate how another Python program can use the presigned URL to upload a file
with open('test-file.txt', 'rb') as f:
    files = {'file': (object_name, f)}
    http_response = requests.post(response['url'], data=response['fields'], files=files)
# If successful, returns HTTP status code 204
print(f'File upload HTTP status code: {http_response.status_code}')

Answer 1

As per document, fields dictionary will not be automatically added to the conditions list. You must specify a condition for the element as well.

response = create_presigned_post(bucket_name, object_name, fields={'x-amz-meta-test_key': 'test-val'}, conditions=[{'x-amz-meta-test_key': 'test-val'}])

It should work :)