javascript - 使用 node.js 编写用于图像上传的过滤器列表的设计模式

Question

我正在用 node.js 和 express 4 编写一个简单的图片 uploader 。当文件被发布时，包含的图片将通过一系列过滤器运行:

• 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 MB 吗？
• 文件在上传时是否被 chop 了？

我习惯于在同步语言中做这种事情，我会通过一系列 if 来运行对象，如果捕捉到某些东西则返回 false。然而，在 javascript 中，相同的方法将导致发送多个 header 。

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？

应用程序.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

好吧，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 Node OOTB 异步功能 also available as sync versions .