node.js -文件系统缓存图像和响应管道图像

Question

我的目标是构建一个简单的文件系统缓存系统，以减少我们需要对缩略图进行API调用的次数。这个过程是检查映像是否已经存在于文件系统fs.stat上，如果不是request，则检查来自API端点的映像，同时将映像写入文件系统。我希望能够同时将请求传递到文件系统和响应，但我认为这是不可能的，所以我首先将响应流流到文件系统，然后创建一个流，将图像从文件系统传输到response对象。

它运行得很好，但我必须相信这是在node.js中完成此任务的一种更有效/优化的方法。有什么想法吗？

    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);
            }
        })
    }

Answer 1

您可以使用ThroughStream来完成这一任务，而不必等待整个文件被写入文件系统。这是因为ThroughStream会在内部缓冲被管道传输到它的数据。

var stream = require('stream')
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 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
            req.pipe(
              new stream.PassThrough().pipe(
                fs.createWriteStream(pathToFile)
              )
            )

            // pipe to the response at the same time
            req.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);
        }
    })
}