ssbbvt - 2017-06-30

Hi, I am trying to modify my bucket policy, so that any object in it are by default publicly readable by http Get. I am trying to use the command: s3cmd setpolicy "policyfile" "s3://bucket".
Could you give me an example of a simple policyfile?
Note that, my hostbase is not amazon.
I tried this policyfile,

{
"Statement": [{
"Sid": "MakeItPublic",
"Effect": "Allow",
"Principal": "",
"Action": "s3:GetObject",
"Resource": "
"
}]

}

But, it failed with the error: S3 error: 400 (InvalidArgument).