Node:S3 policy generator

s3.node.js

//Code adapted from https://gist.github.com/2163005

var s3 = {
  access_key_id: "<Access Key>"
  , secret_key: "<Secret Key>"
  , bucket: "<bucket name>"
  , acl: "public-read"
  , https: "false"
  , error_message: ""
  , pad: function(n) {
    if ((n+"").length == 1) {
      return "0" + n;
    }
    return ""+n;
  }, expiration_date: function() {
    var now = new Date();
    var date = new Date( now.getTime() + (3600 * 1000) );
    var ed = date.getFullYear() + "-" + this.pad(date.getMonth()+1) + "-" + this.pad(date.getDate());
      ed += "T" + this.pad(date.getHours()) + ":" + this.pad(date.getMinutes()) + ":" + this.pad(date.getSeconds()) + ".000Z";
    return ed;
  }
};

app.get('/upload', function(req, res) {
  if(req.query.username == null) {
    res.send(400, "Username not provided");
    return;
  }
  // THIS YOU CHANGE
  aws_access_key = s3.access_key; // your acces key to Amazon services (get if from https://portal.aws.amazon.com/gp/aws/securityCredentials)
  aws_secret_key = s3.secret_key; // secret access key (get it from https://portal.aws.amazon.com/gp/aws/securityCredentials)

  bucket = s3.bucket; // the name you've chosen for the bucket
  key = '/${filename}'; // the folder and adress where the file will be uploaded; ${filename} will be replaced by original file name (the folder needs to be public on S3!)
  success_action_redirect = 'http://localhost:3000/upload/success'; // URL that you will be redirected to when the file will be successfully uploaded
  content_type = 'image/'; // limit accepted content types; empty will disable the filter; for example: 'image/', 'image/png'
  acl = s3.acl; // private or public-read

  // THIS YOU DON'T
  var policy = { "expiration": s3.expiration_date(),
    "conditions": [
      {"bucket": bucket},
      ["starts-with", "$key", str_replace('${filename}', '', key)],
      {"acl": acl},
      {"success_action_redirect": success_action_redirect},
      ["starts-with", "$Content-Type", content_type],
      {"x-amz-meta-uuid": "14365123651275"},
      ["starts-with", "$x-amz-meta-tag", ""]
    ]
  };
  policy = new Buffer(JSON.stringify(policy)).toString('base64').replace(/\n|\r/, '');
  var hmac = crypto.createHmac("sha1", s3.secret_key);
  var hash2 = hmac.update(policy);
  var signature = hmac.digest(encoding="base64");

  res.json(200,{
    bucket: bucket,
    aws_key: aws_access_key,
    acl: acl,
    key: key,
    redirect: success_action_redirect,
    content_type: content_type,
    policy: policy,
    signature: signature
  });
});

//From php.js

function str_replace (search, replace, subject, count) {
  // http://kevin.vanzonneveld.net
  // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   improved by: Gabriel Paderni
  // +   improved by: Philip Peterson
  // +   improved by: Simon Willison (http://simonwillison.net)
  // +    revised by: Jonas Raoni Soares Silva (http://www.jsfromhell.com)
  // +   bugfixed by: Anton Ongson
  // +      input by: Onno Marsman
  // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +    tweaked by: Onno Marsman
  // +      input by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   input by: Oleg Eremeev
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Oleg Eremeev
  // %          note 1: The count parameter must be passed as a string in order
  // %          note 1:  to find a global variable in which the result will be given
  // *     example 1: str_replace(' ', '.', 'Kevin van Zonneveld');
  // *     returns 1: 'Kevin.van.Zonneveld'
  // *     example 2: str_replace(['{name}', 'l'], ['hello', 'm'], '{name}, lars');
  // *     returns 2: 'hemmo, mars'
  var i = 0,
    j = 0,
    temp = '',
    repl = '',
    sl = 0,
    fl = 0,
    f = [].concat(search),
    r = [].concat(replace),
    s = subject,
    ra = Object.prototype.toString.call(r) === '[object Array]',
    sa = Object.prototype.toString.call(s) === '[object Array]';
  s = [].concat(s);
  if (count) {
    this.window[count] = 0;
  }

  for (i = 0, sl = s.length; i < sl; i++) {
    if (s[i] === '') {
      continue;
    }
    for (j = 0, fl = f.length; j < fl; j++) {
      temp = s[i] + '';
      repl = ra ? (r[j] !== undefined ? r[j] : '') : r[0];
      s[i] = (temp).split(f[j]).join(repl);
      if (count && s[i] !== temp) {
        this.window[count] += (temp.length - s[i].length) / f[j].length;
      }
    }
  }
  return sa ? s : s[0];
}

Similar, in repo form: https://github.com/jbuck/s3-post-policy