s3-presigned-url | PreSigned URL for the Amazon S3 via plain HTTP | Cloud Storage library

I would not perform an active lookup in a virtual field. I think it's more conventional to only use it for simple things, with data already present.

I think a model (or table-like object) is a more suitable location for code like this.
You might find this question useful for this point: Cakephp 3 - How to integrate external sources in table?

You can make your own finders (neatly tucked inside Behaviors to group your logic) that combine your AWS data with your database data in this order:

1. Collect database data, produce an array of lookup keys
2. Use the array of keys to perform a single remote lookup
3. Combine the remote data with database data.

You need the s3:GetObject permission to invoke the HeadObject API, which is what the PHP SDK invokes when your code calls doesObjectExist().

If the object you request does not exist, the error Amazon S3 returns depends on whether you also have the s3:ListBucket permission.

• If you have the s3:ListBucket permission on the bucket, Amazon S3 returns an HTTP status code 404 ("no such key") error.
• If you don’t have the s3:ListBucket permission, Amazon S3 returns an HTTP status code 403 ("access denied") error.

So, you probably have s3:ListBucket but not s3:GetObject.

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

You should be able to use the put_object method here. It is a pure client object, rather than a meta client object like upload_file. That is the reason that upload_file is not appearing in client._PY_TO_OP_NAME. The two functions do take different inputs, which may necessitate a slight refactor in your code.

put_object: https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/s3.html#S3.Client.put_object

You can use a similar approach in boto3 with botocore events. The events of interest are "provide-client-params.s3.GetObject" and "before-sign.s3.GetObject". The provide-client-params handler can modify API parameters and context, and before-sign receives among other things the AWSRequest to sign, so we can inject parameters to the URL.

Alright for whoever comes to that issue, here is how I fixed it. In our app logic we now pre signed the url with a given content type of type application/octet-stream (I don't think it does really matter, what matters is to overwrites the "text/plain" that is automatically added by the postman desktop app ) and we send the specified content-type with the postman request.

You can set the endpoint to your bucket domain name:

The solution is to NOT add the header in Postman. Leaving it in the ruby code and removing 'x-amz-acl' parameter from Postman fixed the problem.

When uploading the file, S3 Client will try to determine the correct content type if one hasn't been set . If no content type is provided and cannot be determined by the filename, the default content type, "application/octet-stream", will be used, thus the browser promts you to download the file.

have a look at http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPUT.html