I have been given a task to crawl / parse and index available books on many library web page. I usually use HTML Agility Pack and C# to parse web site content. One of them is the following:
http://bibliotek.kristianstad.se/pls/bookit/pkg_www_misc.print_index?in_language_id=en_GB
If you search for a * (all books) it will return many lists of books, paginated by 10 books per page.
Typical web crawlers that I have found fail on this website. I have also tried to write my own crawler, which would go through all links on the page and generate post/get variables to dynamically generate results. I havent been able to do this as well, mostly due to some 404 errors that I get (although I am certain that the links generated are correct).
The site relies on javascript to generate content, and uses a mixed mode of GET and POST variable submission.
I'm going out on a limb, but try observing the JavaScript GETs and POSTs with Fiddler and then you can base your crawling off of those requests. Fiddler has FiddlerCore, which you can put in your own C# project. Using this, you could monitor requests made in the WebBrowser control and then save them for crawling or whatever, later.
Going down the C# JavaScript interpreter route sounds like the 'more correct' way of doing this, but I wager it will be much harder and frought with errors and bugs unless you have the simplest of cases.
Good luck.
FWIW, the C# WebBrowser control is very, very slow. It also doesn't support more than two simultaneous requests.
Using SHDocVw is faster, but is also semaphore limited.
Faster still is using MSHTML. Working code here: https://svn.arachnode.net/svn/arachnodenet/trunk/Renderer/HtmlRenderer.cs Username/Password: Public (doesn't have the request/rendering limitations that the other two have when run out of process...)
This is headless, so none of the controls are rendered. (Faster).
Thanks,
Mike
If you use the WebBrowser control in a Windows Forms application to open the page then you should be able to access the DOM through the HtmlDocument. That would work for the HTML links.
As for the links that are generated through Javascript, you might look at the ObjectForScripting property which should allow you to interface with the HTML page through Javascript. The rest then becomes a Javascript problem, but it should (in theory) be solvable. I haven't tried this so I can't say.
If the site generates content with JavaScript, then you are out of luck. You need a full JavaScript engine usable in C# so that you can actually execute the scripts and capture the output they generate.
Take a look at this question: Embedding JavaScript engine into .NET -- but know that it will take "serious" effort to do what you need.
AbotX does javascript rendering for you. Its not free though.
Related
So I am just beginning to learn C#, and one of my main goals is to be able to 'navigate' a website. I have done minimal research and have found that the two primary was to do this would be HTTPClient and Requests, and I would like to learn this through HTTPClient.
Now what I mean by navigate is to essentially bot a website for practice. This is like clicking buttons, putting text into fields, etc.
If anyone can give me an idea on where to start with this it would be much appreciated! Not looking for code specifically, just looking for what I should learn in HTTPClient to make this happen. Thanks!
I think that you are a little confused about the concepts. HTTPClient send requests to some site, but you cannot click buttons or "navigate" inside the site.
If youre looking for a way to test some site, i recommend you learn about cypress.io. You can add text to your textboxes, click buttons or navigate in any site. All of this with a few lines of code with Javascript. Its free.
Otherwise, if you need to save values on a database depending of your "navigation", you have to research about scraping tools. I recommend you Selenium or any other scraping tool.
Usually HTTPClient is used when you have to consume a REST API.
Basically you have to think about how a program could ‘see’ a website. You cannot expect to say to the HTTPClient: ‘Open page www.google.com and search for something.’ If you want to do this programmatically you have to exactly specify what your program should do.
For your purpose I recommend the HTML Agility Pack. This one can be used to get the navigation elements of a HTML document. This way you can parse a HTML delivered from a website into your program and do further stuff with it.
Kind regards :)
I'm trying to scrape a particular webpage which works as follows.
First the page loads, then it runs some sort of javascript to fetch the data it needs to populate the page. I'm interested in that data.
If I Get the page with HtmlAgilityPack - the script doesn't run so I get what it essentially a mostly-blank page.
Is there a way to force it to run a script, so I can get the data?
You are getting what the server is returning - the same as a web browser. A web browser, of course, then runs the scripts. Html Agility Pack is an HTML parser only - it has no way to interpret the javascript or bind it to its internal representation of the document. If you wanted to run the script you would need a web browser. The perfect answer to your problem would be a complete "headless" web browser. That is something that incorporates an HTML parser, a javascript interpreter, and a model that simulates the browser DOM, all working together. Basically, that's a web browser, except without the rendering part of it. At this time there isn't such a thing that works entirely within the .NET environment.
Your best bet is to use a WebBrowser control and actually load and run the page in Internet Explorer under programmatic control. This won't be fast or pretty, but it will do what you need to do.
Also see my answer to a similar question: Load a DOM and Execute javascript, server side, with .Net which discusses the available technology in .NET to do this. Most of the pieces exist right now but just aren't quite there yet or haven't been integrated in the right way, unfortunately.
You can use Awesomium for this, http://www.awesomium.com/. It works fairly well but has no support for x64 and is not thread safe. I'm using it to scan some web sites 24x7 and it's running fine for at least a couple of days in a row but then it usually crashes.
There several websites that use AJAX to update the contents periodically and I would like to monitor them. That's why it is necessary to keep multiple webpage windows always open and to grab page sources periodically.
I am searching for an approach for getting HTML sources from these webpages! Could you recommend something? I need it for statistical analysis.
Here are my thoughts so far:
approach. Opening separate Chrome windows manually. Using Handles to find the window. The problem is that it is nearly impossible to grab the HTML of the webpage.. (except the rich text)
Approach. writing an extension for Chrome/Firefox and a C# program. Program will send requests to extension and the extension will return HTML contents of the webpage. That's the theory. Google didn't put my hopes high so I am not sure if that is possible...
Approach. The most realistic one. Using the embed browser such as CefSharp, Awesomium, etc.. But as I mentioned - they have to support multiple opened windows! Any problems here?
So, these are my thought after hours of study..
Personally I would love to implement approach 2 because it is the most awesome.. but others will do too. What would be the easiest and most bulletproof?
Additionaly I would love a feature to do some input operations in these windows. ex: Login/navigate.
If IE browser is an option, look at implementing a managed add-on that will allow you to hook into notifications when document is loaded, access to live DOM of the document, possibly notifications when DOM changes, and so on. The same can be done in FF/Chrome. With IE, look into IObjectWithSite COM interface. This article seems to be a decent tutorial, though I'm not vouching for its accuracy.
I'd like to create a web page where you can enter your domain name and have it fetch it and show you all the resources, their download times, etc -- similar to FireFox's NET tab.
Here's the page which I'd like emulate: http://tools.pingdom.com/
Now, I know this is a complex feature, but I'd like to hear general ideas. I know I could easily fetch the HTML via a WebClient, but that's the easy part. I need to fetch and time all the resources too, and not all at the same time. I want to mimic a browser. So, I thought about using something like System.Windows.Forms.WebBrowser, but that will only really give me the page load time.
Anyone have any thoughts / tips?
Using the Html Agility Pack you can easily find which external resources are referenced from an HTML page.
This won't tell you exactly when they would be loaded by the browser, and also won't help you with dynamically loaded resources, but is a good start.
I'm afraid the only way to be sure is to instantiate an entire browser. You could use a plug in for the Fiddler HTTP debugging proxy to intercept requests from the WebBrowser control to determine which resources are actually loaded in this case.
I have a webcrawler application. It successfully crawled most common and simple sites. Now i ran into some types of websites wherein HTML documents are dynamically generated through FORMS or javascripts. I believe they can be crawled and I just don't know how. Now, these websites do not show the actual HTML page. I mean if I browse that page in IE or firefox, the HTML code does not match what's actually in the IE or firefox. These sites contain textboxes, checkboxes, etc... so I believe they are what they call "Web Forms". Actually I am not much familiar with web development so correct me if I'm wrong.
My question is, does anyone in similar situation as I am now and have successfully solved these types of "challenges"? Does anyone know of a certain book or article regarding web crawling? Those that pertains to these advanced type of websites?
Thanks.
There are two separate issues here.
Forms
As a rule of thumb, crawlers do not touch forms.
It might be appropriate to write something for a specific website, that submits predetermined (or semi-random) data (particularly when writing automated tests for your own web applications), but generic crawlers should leave them well alone.
The spec describing how to submit form data is available at http://www.w3.org/TR/html4/interact/forms.html#h-17.13, there may be a library for C# that will help.
JavaScript
JavaScript is a rather complicated beast.
There are three common ways you can deal with it:
Write your crawler so it duplicates the JS functionality of specific websites that you care about.
Automate a web browser
Use something like Rhino with env.js
I found an article which tackles deep web and its very interesting and I think this answers my questions above.
http://www.trycatchfail.com/2008/11/10/creating-a-deep-web-crawler-with-net-background/
Gotta love this.
AbotX handles javascript out of the box. Its not free though.