使用 node.js 编写图像上传过滤器列表的设计模式

Question

我正在node.js写一个简单的图片上传器并表达4。当文件被发布时，附上的图片会运行通过一系列的过滤器：

这是可接受的 MIME 类型吗？ (jpg, gif, png, tiff)
这是否有相应的可接受的扩展名？
这张图片小于 2 兆字节吗？
上传的文件是否已被分类运行？

我习惯在同步语言中做这种事情，我会运行通过一系列 if 的 object ，如果捕获到 return false 。然而，在 javascript 中，相同的方法将导致发送多个 headers.

我已经通过在 else 子句中嵌套过滤器来解决这个问题，但这很快就会变得非常笨拙。这似乎是一种常见的设计模式，那么处理此类问题的最佳方法是什么？

app.js:

var express     = require('express')
 ,  fs          = require('fs')
 ,  bodyParser  = require('body-parser')
 ,  serveStatic = require('serve-static')
 ,  multer      = require('multer')
 ,  port        = 80
 ;

var app = express();
app.set('views', __dirname + '/views');
app.set('view engine', 'jade');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(multer({ dest: "./images/tmp" }))
app.use(serveStatic(__dirname + '/public'));
app.listen(port);

app.get('/', function(req, res, next) {
    console.log(req);
    res.render("uploader");
});

var uploadConfig = {
    acceptedMimeTypes : [ "image/jpeg", "image/png", "image/gif", "image/tiff" ],
    acceptedExtensions : [ "jpg", "jpeg", "png", "gif", "tiff" ],
    maxFileSize : 2000000
};

app.post('/upload', function(req, res, next) {
    var image = req.files.image;
    var removeTempImage = function() {
        fs.unlink('images/tmp/' + image.name)
    };
   // Here is where things become a mess
    if (uploadConfig.acceptedMimeTypes.indexOf(image.mimetype) == -1) {
        removeTempImage();
        res.send({success: false, message: "Incorrect MIME type"});
    } else {
        if (uploadConfig.acceptedExtensions.indexOf(image.extension) == -1) {
            removeTempImage();
            res.send({success: false, message: "Incorrect file extension"});
        } else {
            if (image.size > uploadConfig.maxFileSize) {
                removeTempImage();
                res.send({success: false, message: "File is too large"});
            } else {
                if (image.truncated) {
                    removeTempImage();
                    res.send({success: false, message: "The file was truncated"});      
                } else {
                    // it survived the gauntlet
                    fs.rename('images/tmp/' + image.name, 'public/completeImgs/' + image.name, function (err) {
                        if (err) {
                            removeTempImage;
                            res.send({success: false, message: err});
                        } else {
                            res.send({success: true, message: "Your image has been saved"});
                        }
                    })
                }
            }
        }
    }
});


console.log("uploader is listening on port " + port);

uploader.jade

doctype
html
    head
    body
        h1 Image Uploader
        form(method="post" action="/upload" enctype="multipart/form-data")
            input(type="file" name="image")
            input(type="submit")
        h1 !{test}

Answer 1

您可以使用 Promise 库，例如 BlueBird:

Promise.resolve(image)
    .then(function(image) {
        if (uploadConfig.acceptedMimeTypes.indexOf(image.mimetype) == -1) {
            throw "Incorrect MIME type";
        }
        return image;
    })
    .then(function(image) {
        if (image.size > uploadConfig.maxFileSize) {
            throw "File is too large";
        }
        return image;
    })
    .then(function(image) {
        if (image.truncated) {
            throw "The file was truncated";
        }
        return image;
    })
    .then(function(image) {
        return fs.renameAsync('images/tmp/' + image.name, 'public/completeImgs/' + image.name)
    })
    .then(function(err) {
        if (err)
            throw err;
    })
    .then(function() {
        res.send({success: true, message: "Your image has been saved"});
    })
    .catch(function(err) {
        removeTempImage();
        res.send({success: false, message: err});
    });

Answer 2

我自己还没有使用过 multer，但是如果您查看 multer 页面，它有很多选项，其中之一至少可以让您消除尺寸检查。 https://www.npmjs.com/package/multer。此外，您不必在此处执行任何异步操作。当您的 post 函数被调用时，multer 对象已经填写完毕，文件正在等待您。

但是像这样的事情呢:

var error_messages = '';
if (uploadConfig.acceptedMimeTypes.indexOf(image.mimetype) == -1) {
    error_messages = "Incorrect MIME type ";
}
if (uploadConfig.acceptedExtensions.indexOf(image.extension) == -1) {
    error_messages += "Incorrect file extension ";
}
if (image.size > uploadConfig.maxFileSize) {
    error_messages +=  "File is too large ");
}
if (image.truncated) {
    error_messages +=  "The file was truncated ";      
}

if(error_messages === ''){
    fs.rename('images/tmp/' + image.name, 'public/completeImgs/' + image.name, function (err) {
        if (err) {
            removeTempImage;
            res.send({success: false, message: err});
        }
        else {
            res.send({success: true, message: "Your image has been saved"});
        }
    });
}
else {
    res.send({success: false, message: error_messages});
}

无可否认，像那样连接错误消息是胡说八道。您可以将它们放在一个数组中并将该数组传递给视图或其他东西。

Answer 3

嗯，你所有的支票都是同步的。就这样吧：

app.post('/upload', function (req, res, next)
{
    var image = req.files.image;
    var removeTempImage = function ()
    {
        fs.unlink('images/tmp/' + image.name)
    };

    // Here is where things become a mess
    if (uploadConfig.acceptedMimeTypes.indexOf(image.mimetype) == -1)
    {
        removeTempImage();
        res.send({ success: false, message: "Incorrect MIME type" });
        return;
    }

    if (uploadConfig.acceptedExtensions.indexOf(image.extension) == -1)
    {
        removeTempImage();
        res.send({ success: false, message: "Incorrect file extension" });
        return;
    }

    if (image.size > uploadConfig.maxFileSize)
    {
        removeTempImage();
        res.send({ success: false, message: "File is too large" });
        return;
    }

    if (image.truncated)
    {
        removeTempImage();
        res.send({ success: false, message: "The file was truncated" });
        return;
    }

    // it survived the gauntlet
    fs.rename('images/tmp/' + image.name, 'public/completeImgs/' + image.name, function (err)
    {
        if (err)
        {
            removeTempImage;
            res.send({ success: false, message: err });
        } else
        {
            res.send({ success: true, message: "Your image has been saved" });
        }
    });
});

此外，大多数节点 OOTB 异步功能 also available as sync versions。

使用 node.js 编写图像上传过滤器列表的设计模式

Design pattern for writing a list of filters for image uploading using node.js

javascript

design-patterns

file-upload

node.js

express