使用安全json parser防止json注入

有些程序员如果没有很好的在javascript中解析json数据，往往会直接eval把json转成js对象，这时候如果json的数据中包含了被注入的恶意数据，则可能导致代码注入的问题。

正确的做法是分割出json里包含的特殊字符，然后再解析为对象
http://json.org/json2.js 中是通过正则来完成的。

// We split the second stage into 4 regexp operations in order to work around

// crippling inefficiencies in IE's and Safari's regexp engines. First we

// replace the JSON backslash pairs with '@' (a non-JSON character). Second, we

// replace all simple value tokens with ']' characters. Third, we delete all

// open brackets that follow a colon or comma or that begin the text. Finally,

// we look to see that the remaining characters are only whitespace or ']' or

// ',' or ':' or '{' or '}'. If that is so, then the text is safe for eval.

if (/^[\],:{}\s]*$/.

test(text.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@').

replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']').

replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) {

// In the third stage we use the eval function to compile the text into a

// JavaScript structure. The '{' operator is subject to a syntactic ambiguity

// in JavaScript: it can begin a block or an object literal. We wrap the text

// in parens to eliminate the ambiguity.

j = eval('(' + text + ')');

目前不少写的好的框架和js解析函数都取用了这种做法。

所以，以后千万别直接eval了。