Error on S3 Policy with FineUploader in Rails - ruby-on-rails

Question

I have been trying to implement direct upload to S3 using the FineUploader JS library. I have a post action in Rails that builds and returns a S3 policy and signature, I have tried many different options but I keep getting an error with the policy in FineUploader.
Here is the FineUploader JS I am using:
<script>
$('#fine-uploader-s3').fineUploaderS3({
template: 'qq-template-s3',
request: {
endpoint: "https://mybucket.s3.amazonaws.com/",
accessKey: MY_ACCESS_KEY
},
signature: {
endpoint: "/generatesignature"
},
uploadSuccess: {
endpoint: "/success",
params: {
isBrowserPreviewCapable: qq.supportedFeatures.imagePreviews
}
},
iframeSupport: {
localBlankPagePath: "/server/success.html"
},
cors: {
expected: true
},
chunking: {
enabled: true
},
resume: {
enabled: true
},
deleteFile: {
enabled: true,
method: "POST",
endpoint: "http://s3-demo.fineuploader.com/s3demo-thumbnails-cors.php"
},
validation: {
itemLimit: 5,
sizeLimit: 15000000
},
thumbnails: {
placeholders: {
notAvailablePath: "/plugins/fineuploader/placeholders/not_available-generic.png",
waitingPath: "/plugins/fineuploader/placeholders/waiting-generic.png"
}
},
callbacks: {
onComplete: function(id, name, response) {
var previewLink = qq(this.getItemByFileId(id)).getByClass('preview-link')[0];
if (response.success) {
previewLink.setAttribute("href", response.tempLink)
}
}
}
});
</script>
Here is the generatesignature action serverside in Ruby
def generatesignature
bucket = MY_BUCKET
access_key = MY_ACCESS_KEY
secret = MY_SECRET_KEY
key = "test.txt/"
expiration = 5.minutes.from_now.utc.strftime('%Y-%m-%dT%H:%M:%S.000Z')
max_filesize = 2.megabytes
acl = 'public-read'
sas = '200' # Tells amazon to redirect after success instead of returning xml
policy = Base64.encode64(
"{'expiration': '#{expiration}',
'conditions': [
{'bucket': '#{bucket}'},
{'acl': '#{acl}'},
{'Cache-Control': 'max-age=31536000'},
['starts-with', '$key', '#{key}'],
['content-length-range', 1, #{max_filesize}]
]}
").gsub(/\n|\r/, '')
signature = Base64.encode64(OpenSSL::HMAC.digest(OpenSSL::Digest::Digest.new('sha1'), secret, policy)).gsub(/\n| |\r/, '')
{:access_key => access_key, :key => key, :policy => policy, :signature => signature, :sas => sas, :bucket => bucket, :acl => acl, :expiration => expiration}
params[:signature]= signature
params[:policy] = policy
render :json => params, :status => 200 and return
end
The error that I am receiving when trying to upload to S3 is:
"Invalid according to Policy: Policy Condition failed: ["eq", "$acl", "public-read"]"

Answer 1

It appears as if you are generating a signature using an ACL value of "public-read", but the policy sent to S3 by Fine Uploader, by default, uses an ACL of "private". If you really want to use a "public-read" ACL, you will need to update the objectProperties.acl Fine Uploader S3 configuration value. For example:
$('#fine-uploader-s3').fineUploaderS3({
objectProperties: {
acl: 'public-read'
},
...
})