title: node.js - Cache Image to Filesystem and Pipe Image to Response
body: <p>My goal is to construct a simple filesystem caching system for reducing the number of calls we need to make to an API for thumbnail images. The process is to check if the image already exists on the filesystem <code>fs.stat</code> and if not <code>request</code> the image from an API endpoint while at the same time writing the image to the file system. I was hoping I could pipe the request to both the file system and the response at the same time, but I don't believe that is possible so I first stream the response to the file system and then create a stream to pipe the image from the file system to the <code>response</code> object.</p>
  
  <p>It's working well, but I have to believe that is a more efficient/optimized way to do this task in node.js. Any thoughts?</p>
  
  <pre><code>    function (req, res, next) {
  
          // Check to see if the image exists on the filesystem
          // TODO - stats will provide information on file creation date for cache checking
          fs.stat(pathToFile, function (err, stats) {
              if (err) {
  
                  // If the image does not exist on the file system
                  // Pipe the image to a file and then to the response object
                  var req = request.get({
                      "uri": "http://www.example.com/image.png",
                      "headers": {
                          "Content-Type": "image/png"
                      }
                  });
  
                  // Create a write stream to the file system
                  var stream = fs.createWriteStream(pathToFile);
                  req.pipe(stream);
                  stream.on('finish', function () {
                      fs.createReadStream(pathToFile)
                          .pipe(res);
                  })
              }
              else {
  
                  // If the image does exist on the file system, then stream the image to the response object
                  fs.createReadStream(pathToFile)
                      .pipe(res);
              }
          })
      }
  </code></pre>