灾难性的回溯问题

Question

如果找不到匹配项，我遇到了正则表达式模式的问题。

我用的正则表达式是：

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

测试数据我使用的喜欢的东西：

"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“路由”参数被发现，一切运作良好。但是，如果通过排除测试数据找不到路由参数，那么正则表达式将继续搜索。我发现其他帖子发现这是由灾难性的回溯造成的，但我似乎无法找到避免它的方法。

Answer 1

缩小你的问题：

如何避免灾难性的回溯？

正则表达式的一面：要尽可能具体，如Rawing在他的评论中说，改变".*?"到"[^"]*"将大大减少所需原路返回的数量发动机。

输入站点：如果可能，将输入减少到所需的最小部分，而不会丢失信息。这里，从改变你的输入：

"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=(.*?); 

将有很大的帮助。