How to convert a JSON object to a base64 string?

Question

I am trying to run an Amazon example of downloading browser-based files on S3 using POST.

An example shows this JSON policy ...

{ "expiration": "2013-08-06T12:00:00.000Z",
  "conditions": [
    {"bucket": "examplebucket"},
    ["starts-with", "$key", "user/user1/"],
    {"acl": "public-read"},
    {"success_action_redirect": "http://acl6.s3.amazonaws.com/successful_upload.html"},
    ["starts-with", "$Content-Type", "image/"],
    {"x-amz-meta-uuid": "14365123651274"},
    ["starts-with", "$x-amz-meta-tag", ""],

    {"x-amz-credential": "AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
    {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
    {"x-amz-date": "20130806T000000Z" }
  ]
}

... and says that this is a base64 based encoded version:

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

However, when I do this from Node.js REPL ...

var policy = {
  "expiration": "2013-08-06T12:00:00.000Z",
  "conditions": [
    {"bucket": "examplebucket"},
    ["starts-with", "$key", "user/user1/"],
    {"acl": "public-read"},
    {"success_action_redirect": "http://acl6.s3.amazonaws.com/successful_upload.html"},
    ["starts-with", "$Content-Type", "image/"],
    {"x-amz-meta-uuid": "14365123651274"},
    ["starts-with", "$x-amz-meta-tag", ""],

    {"x-amz-credential": "AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
    {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
    {"x-amz-date": "20130806T000000Z" }
  ]
};

console.log(new Buffer(JSON.stringify(policy)).toString('base64'));

... I get another base64 string:

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

Am I doing something wrong, or is there an error in the Amazon example?

Answer 1

The difference is obvious if you just canceled base64 encoding on both results.

( atob()decodes base64, btoa()encodes it)

Amazon example:

atob('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')
"{ "expiration": "2013-08-07T12:00:00.000Z",
  "conditions": [
    {"bucket": "examplebucket"},
    ["starts-with", "$key", "user/user1/"],
    {"acl": "public-read"},
    {"success_action_redirect": "http://examplebucket.s3.amazonaws.com/successful_upload.html"},
    ["starts-with", "$Content-Type", "image/"],
    {"x-amz-meta-uuid": "14365123651274"},
    ["starts-with", "$x-amz-meta-tag", ""],

    {"x-amz-credential": "AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},
    {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
    {"x-amz-date": "20130806T000000Z" }
  ]
}"

Your result:

atob('eyJleHBpcmF0aW9uIjoiMjAxMy0wOC0wNlQxMjowMDowMC4wMDBaIiwiY29uZGl0aW9ucyI6W3siYnVja2V0IjoiZXhhbXBsZWJ1Y2tldCJ9LFsic3RhcnRzLXdpdGgiLCIka2V5IiwidXNlci91c2VyMS8iXSx7ImFjbCI6InB1YmxpYy1yZWFkIn0seyJzdWNjZXNzX2FjdGlvbl9yZWRpcmVjdCI6Imh0dHA6Ly9hY2w2LnMzLmFtYXpvbmF3cy5jb20vc3VjY2Vzc2Z1bF91cGxvYWQuaHRtbCJ9LFsic3RhcnRzLXdpdGgiLCIkQ29udGVudC1UeXBlIiwiaW1hZ2UvIl0seyJ4LWFtei1tZXRhLXV1aWQiOiIxNDM2NTEyMzY1MTI3NCJ9LFsic3RhcnRzLXdpdGgiLCIkeC1hbXotbWV0YS10YWciLCIiXSx7IngtYW16LWNyZWRlbnRpYWwiOiJBS0lBSU9TRk9ETk43RVhBTVBMRS8yMDEzMDgwNi91cy1lYXN0LTEvczMvYXdzNF9yZXF1ZXN0In0seyJ4LWFtei1hbGdvcml0aG0iOiJBV1M0LUhNQUMtU0hBMjU2In0seyJ4LWFtei1kYXRlIjoiMjAxMzA4MDZUMDAwMDAwWiJ9XX0=')
"{"expiration":"2013-08-06T12:00:00.000Z","conditions":[{"bucket":"examplebucket"},["starts-with","$key","user/user1/"],{"acl":"public-read"},{"success_action_redirect":"http://acl6.s3.amazonaws.com/successful_upload.html"},["starts-with","$Content-Type","image/"],{"x-amz-meta-uuid":"14365123651274"},["starts-with","$x-amz-meta-tag",""],{"x-amz-credential":"AKIAIOSFODNN7EXAMPLE/20130806/us-east-1/s3/aws4_request"},{"x-amz-algorithm":"AWS4-HMAC-SHA256"},{"x-amz-date":"20130806T000000Z"}]}"

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