How to generate AWS S3 pre-signed URL request without knowing Content-Type?

Question

I am generating in server side a pre-signed URL request with the following parameters for GeneratePresignedUrlRequest : bucket, key, expiration = in 1 hour and method = PUT.

In my Angular app, I am uploading the file using ng-file-upload

Upload.http({
    url: $scope.signedUrl,
    method: "PUT",
    headers : {
        'Content-Type': $scope.file.type
    },
    data: $scope.file
});

The problem is that I always have a 403 response unless I set the type of the file in GeneratePresignedUrlRequest.contentType.

The problem is that I can't predict in advance what type of file the user will choose (image/png, image/jpeg, text/plain...).

How can I generate a pre-signed url that accept all kinds of content-type ? I tried setting it to null, it keeps sending 403 errors.

Thanks.

Solution 1

I just ran into this problem, and just got it working. Replace your Upload.http code with the following:

var reader = new FileReader();
var xhr = new XMLHttpRequest();

xhr.open("PUT", $scope.signedUrl);
reader.onload = function(evt) {
  xhr.send(evt.target.result);
};
reader.readAsArrayBuffer($scope.file);

The problem ends up being that S3 is looking for a specific Content-Type (binary/octet-stream), which it infers when you omit the Content-Type header.

Solution 2

The value from the Content-Type header is a mandatory component of the signature. It isn't possible to pre-sign a PUT URL without knowing the value that will be sent.

A POST upload is more flexible, since you can allow any Content-Type in the signed policy.

Comments

[c4k]

What do you mean by POST upload ? Get the pre-signed URL with POST, no content-type and POST instead of PUT in my Angular app ?

[Michael - sqlbot]

It doesn't particularly matter how you get the authorization from your back-end, but S3 has a very different interface for form-based uploads using a POST from the browser that seems to be a better match for what you are doing, at least in this one sense: docs.aws.amazon.com/AmazonS3/latest/API/sigv4-post-example.h‌​tml

[Michael - sqlbot]

Actually, you might start here: docs.aws.amazon.com/AmazonS3/latest/API/…

[c4k]

Thanks but I can't use HTML POST form. The form needs to be independant.

[Michael - sqlbot]

You technicallyvdon't have to "use" (build, render, or display) a form, you only have to submit the structure of a form back to S3.

[okigan]

This does not address core part of the question: cannot predict file type in advance