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现状: 冗余

\r\n
在web开发中，我们是否常常会使用不同的编程语言实现相同的功能？\r\n
\r\n
如一个文件上传功能，需要对上传文件进行文件格式限制。我们通常会使用后缀名做限制。\r\n

前端

\r\n
为了用户体验，会在页面对用户选择的文件进行判断，合法才让用户可以上传。\r\n

function is_filetype(filename, types) {\r\n
    types = types.split(',');\r\n
    var pattern = '\\.(';\r\n
    for(var i=0; i        if(0 != i) {\r\n
            pattern += '|';\r\n
        }\r\n
        pattern += types[i].trim();\r\n
    }\r\n
    pattern += ')$';\r\n
    return new RegExp(pattern, 'i').test(filename);\r\n
};\r\n
\r\n
// 此处省略N行代码\r\n
if(!is_filetype($('#uploadfile').val(), 'doc,pdf,txt,wps,odf,md,png,gif,jpg')){\r\n
    can_submit = false; // 不允许上传\r\n
    $('#uploadfile').val('');\r\n
    alert('只允许上传: ' + constant.RESUME_FILETYPES);\r\n
}\r\n
// 此处省略N行代码

\r\n

后端

\r\n
由于担心恶意上传，无法避免地需要重新对用户上传的文件进行判断。\r\n
于是我又用python写了一个判断文件后缀的逻辑\r\n

import re\r\n
\r\n
def is_filetype(filename, types):\r\n
    types = types.split(',')\r\n
    pattern = '\\.(' + '|'.join([t.strip() for t in types]) + ')$';\r\n
    return re.search(pattern, filename, re.I) != None\r\n
\r\n
# web request handler\r\n
# 此处省略N行代码

\r\n

导致这样重复工作的原因是为什么？

\r\n

前端永远不可信；

前端和后端使用不同的编程语言；

\r\n

这样的冗余会带来什么代价？

\r\n

修改业务逻辑，需要重复做2次：如突然发现少支持了 docx 文件类型，需要同时修改javascript代码和python代码

增加确保javascript代码和python代码业务逻辑一致的代价。需要分别写2种测试，unit test跑多一倍。

\r\n

nodejs时代：DRY

\r\n
Use nodejs no more DRY !\r\n

一份代码，前端后端同时运行

\r\n

// constant.js\r\n
(function(exports){\r\n
\r\n
exports.RESUME_FILETYPES = 'doc,docx,pdf,txt,wps,odf,md,png,gif,jpg';\r\n
\r\n
})( (function(){\r\n
    if(typeof exports === 'undefined') {\r\n
        window.constant = {};\r\n
        return window.constant;\r\n
    } else {\r\n
        return exports;\r\n
    }\r\n
})() );\r\n
\r\n
// util.js\r\n
(function(exports){\r\n
\r\n
/**\r\n
 * 移除字符串两端的空白字符\r\n
 *\r\n
 * [@return](/user/return) {String}\r\n
 * [@api](/user/api) public\r\n
 */\r\n
String.prototype.trim = function(){ \r\n
    return this.replace(/(^\\s*)|(\\s*$)/g, \"\"); \r\n
};\r\n
\r\n
/**\r\n
 * 判断是否自定类型的文件\r\n
 * \r\n
 * [@param](/user/param) {String}filename\r\n
 * [@param](/user/param) {String}types, 多个类型使用,号分隔，如 doc,docx,txt\r\n
 * [@return](/user/return) {Boolean} true or false\r\n
 * [@api](/user/api) public\r\n
 */\r\n
var is_filetype = exports.is_filetype = function(filename, types) {\r\n
    types = types.split(',');\r\n
    var pattern = '\\.(';\r\n
    for(var i=0; i        if(0 != i) {\r\n
            pattern += '|';\r\n
        }\r\n
        pattern += types[i].trim();\r\n
    }\r\n
    pattern += ')$';\r\n
    return new RegExp(pattern, 'i').test(filename);\r\n
};\r\n
\r\n
})( (function(){\r\n
    if(typeof exports === 'undefined') {\r\n
        window.util = {};\r\n
        return window.util;\r\n
    } else {\r\n
        return exports;\r\n
    }\r\n
})() );

\r\n

前端

\r\n

\r\n
\r\n
\r\n
// 此处省略N行代码\r\n
if(!util.is_filetype($('#uploadfile').val(), constant.RESUME_FILETYPES)){\r\n
    can_submit = false; // 不允许上传\r\n
    $('#uploadfile').val('');\r\n
    alert('只允许上传: ' + constant.RESUME_FILETYPES);\r\n
}\r\n
// 此处省略N行代码

\r\n

后端

\r\n

var util = require('./public/js/util.js'),\r\n
    constant = require('./public/js/constant.js');\r\n
app.post('/resume/upload/:job_id', function(req, res, next){\r\n
    req.form.complete(function(err, fields, files){\r\n
        if(!util.is_filetype(filepath, constant.RESUME_FILETYPES)) {\r\n
            // 由于客户端已做判断，所以这样的情况都是恶意上传的，直接提示\r\n
            res.send('文件格式错误: ' + filepath \r\n
                + ' , 请上传' + constant.RESUME_FILETYPES + '格式的文件');\r\n
            return;\r\n
        }\r\n
        // save file ... \r\n
        // 此处省略N行代码\r\n
    });\r\n
});

\r\n
wow，没冗余了吧！done\r\n

其他常用场景

\r\n

常量定义

各种有用的工具模块，如字符串操作

\r\n

有爱

\r\n
^_^ 希望本文对你有帮助","title","nodejs: 真正的一份代码，到处运行","last_reply_at","2013-01-21 08:34:03.027","good","top",22,"visit_count",15621,"2011-03-30 04:04:39","author",{"_13":54,"_22":55},"fengmk2","https://avatars.githubusercontent.com/u/156269?v=4"]