text: var fs = require("fs");
  var path = require("path");
  
  try {
      fs.mkdirSync("./tmp");
  } catch (e) {
      if (e.code != "EEXIST") throw e;
  }
  
  function local(url) {
      return path.join("./tmp", encodeURIComponent(url));
  }
  
  function read(url) {
      return fs.createReadStream(local(url));
  }
  
  module.exports = function(url, callback) {
      var result = read(url);
      result.on("error", function(e) {
          if (e.code != "ENOENT") return callback(e);
          require(url.slice(0, url.indexOf(":"))).get(url, function(res) {
              if (res.statusCode !== 200) return callback(res);
              res.pipe(fs.createWriteStream(local(url)).on("close", function() {
                  callback(null, read(url));
              }));
          });
      }).on("open", function() {
          callback(null, result);
      });
  };
  