What's the principle of web scanning softwares? [closed]

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How can it scan all available pages automatically?

One way I can think of is to scan it recursively from the home page.

But it won't be able to scan out the back end CMS .

So开发者_如何学Go how do those scanning tools work?

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Stupid web crawler:

Start by creating an array to store links, and putting one URL in there yourself. Create a second empty array to store visited URLs. Now start a program which does the following.

1. Read and remove first item in the link array
2. Download webpage at that URL
3. Parse HTML for link tags, add all links found to the link array
4. Add the webpage URL to the visited URL array
5. Goto 1

If you assume that every page on the web is reachable by following some number of random links (possibly billions), then simply repeating steps 1 through 4 will eventually result in downloading the entire web. Since the web is not actually a fully connected graph, you have to start the process from different points to eventually reach every page.