C# Web Page Capture Library: HtmlAgilityPack Tutorial

HtmlAgilityPack + Proxy IP double sword when crawler meets anti-climbing?

What is the biggest headache for the old iron people to do web crawling? Nine times out of ten, the IP is blocked! Today, let's talk about how to use C's HtmlAgilityPack with theipipgo proxy ip service, creating a crawler system that is both stable as an old dog and resistant to blocking.

HtmlAgilityPack First Experience

This thing is equivalent to C installed a web page parsing plug-ins, use than regular expressions to save a lot of heart. For example, you want to catch the price of an e-commerce site:

var web = new HtmlWeb(); var doc = web.
var doc = web.Load("https://目标网站"); var priceNode = doc.
var priceNode = doc.DocumentNode.SelectSingleNode("//span[@class='price']");
Console.WriteLine(priceNode.InnerText);

But so straight ball operation, not out of three days is absolutely blocked IP!Armor - ipipgo proxy ipThe

The right way to open a proxy IP

To HtmlWeb set of proxy is actually very simple, the focus is to use a reliable proxy pool. Take ipipgo for example, their API looks like this:

var proxy = new WebProxy("gateway.ipipgo.com:8000", true) {
    Credentials = new NetworkCredential("Your account", "Password")
};

var web = new HtmlWeb();
web.PreRequest = request => {
    request.Proxy = proxy; }; var web = new HtmlWeb()
    request.Proxy = proxy; return true; }; var web = new HtmlWeb(); web.
}; }

Delineate the focus:Remember to whitelist IPs in the ipipgo backendOtherwise the authentication will fail. The actual test with their dynamic residential agent, caught for 2 weeks in a row did not trigger the anti-climbing mechanism.

Agent Parameter Tuning Tips

Here's a parameter cross-reference table that works in person:

Remember to put random delays in the code, don't be on time like a robot:

var rand = new Random();
Thread.Sleep(rand.Next(1000, 5000)); // randomly sleep for 1-5 seconds

A practical guide to avoiding the pit

Pothole 1: SSL Certificate Error Reporting
Remember to add this when using ipipgo's HTTPS proxy:

ServicePointManager.ServerCertificateValidationCallback = (s, cert, chain, errors) => true;

Pitfall 2: Sudden failure of the proxy
It is recommended to have a proxy health check, and switch immediately when it is found to be unavailable. ipipgo's API supports getting a list of available IPs in real time, which is a very useful feature.

Frequently Asked Questions

Q: Why is it still blocked after using a proxy?
A: Check if you are using a transparent proxy, choose ipipgo's high stash of proxies, the request header will not expose the proxy information

Q: Does changing IPs for each request affect speed?
A: ipipgo's response time is basically within 200ms, measured millions of data collection, with their dynamic agent than not using the agent is also faster than 30% (because of the reduction of the blocking retry)

Q: Do free proxies work?
A: Brother, free is the most expensive! Previously tested, the free agent's availability is less than 5%, ipipgo enterprise package's availability can reach 99.8%, the key is to save ah!

Finally, a word from the heart: the web crawler thing.Seven points are based on skill, three points on agencyThe best way to use HtmlAgilityPack is to use it. Using a good HtmlAgilityPack is the foundation, pairing it with a professional proxy service like ipipgo is the way to go. Their proxy pool is updated frequently, especially thatDynamic Residential IPThe simulation of real user access to the effect of the thief, who uses who knows!