灾难性的回溯问题

Question

当找不到匹配项时，我运行遇到了正则表达式模式的问题。

我使用的正则表达式模式是：

^(?:".*?",){4}"(?:.*?)Cookie:\s(?:.*?)Routing=(.*?);

作为测试数据，我使用了类似的东西：

"a","b","c","d","POST: /portal/start.asp HTTP/1.1\r\nHost: myhost\r\nCookie: w1n0_er=xxxx; routxing=yyyy;"x","x","x","x","x","x","x","x","x","x","x","x","x","x","x","x","x",

当找到 'routing' 参数时，一切正常。但是，当通过从测试数据中排除它找不到路由参数时，正则表达式会继续搜索。我通过其他帖子发现这是由灾难性回溯引起的，但我似乎无法找到避免它的方法。

Answer 1

将您的问题缩小到：

How to avoid catastrophic backtracking?

正则表达式方面：尽可能具体，正如 Rawing 在他的评论中所说，将 ".*?" 更改为 "[^"]*" 将大大减少引擎所需的回溯次数。

输入站点：如果可能，在不丢失信息的情况下将输入减少到您需要的最小部分。在这里，将您的输入更改为：

"a","b","c","d","POST: /portal/start.asp HTTP/1.1\r\nHost: myhost\r\nCookie: w1n0_er=xxxx; routxing=yyyy;"x","x","x","x","x","x","x","x","x","x","x","x","x","x","x","x","x",

到

"POST: /portal/start.asp HTTP/1.1\r\nHost: myhost\r\nCookie: w1n0_er=xxxx; Routing=yyyy;"

和正则表达式：

^".*?Cookie:\s.*?Routing=(.*?);

会有很大帮助。

灾难性的回溯问题

Catastrophic backtracking issue

regex

backtracking