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 :)
Related
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 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.
I need to write a C# code for grabbing contents of a web page. Steps looks like following
Browse to login page
I have user name and a password, provide it programatically and login
Then you are in detail page
You have to get some information there, like (prodcut Id, Des, etc.)
Then need to click(by code) on Detail View
Then you can get the price for that product from there.
Now it is done, so we can write detail line into text file like this...
ABC Printer::225519::285.00
Please help me on this, (Even VB.Net Code is ok, I can convert it to C#)
The WatiN library is probably what you want, then. Basically, it controls a web browser (native support for IE and Firefox, I believe, though they may have added more since I last used it) and provides an easy syntax for programmatically interacting with page elements within that browser. All you'll need are the names and/or IDs of those elements, or some unique way to identify them on the page.
You should be able to achieve this using the WebRequest class to retrieve pages, and the HTML Agility Pack to extract elements from HTML source.
yea I downloaded that library. Nice one.
Thanks for sharing it with me. But I have a issue with that library. The site I want to get data is having a "captcha" on the login page.
I can enter that value if this can show image and wait for my input.
Can we achive that from this library, if you can like to have a sample.
You should be able to achieve this by using two classes in C#, HttpWebRequest (to request the web pages) and perhaps XmlTextReader (to parse the HTML/XML response).
If you do not wish to use XmlTextReader, then I'd advise looking into Regular Expressions, as they are fantastically useful for extracting information from large bodies of text where-in patterns exist.
How to: Send Data Using the WebRequest Class
I'm currently using the HTML Agility Pack in C# for a web crawler. I've managed to avoid many issues so far (Invalid URIs, such as "/extra/url/to/base.html" and "#" links), but I also need to process PHP, Javascript, etc. Like for some sites, the links are in PHP, and when my web crawler tries to navigate to these, it fails. One example is a PHP/Javascript accordion link page. How would I go about navigating/parsing these links?
Lets see if I understood your question correctly. I'm aware that this answer is probably inadequate but if you need a more specific answer I'd need more details.
You're trying to program a web crawler but it cannot crawl URLs that end with .php?
If that's the case you need to take a step back and think about why that is. It could be because the crawler chooses which URLs to crawl using a regex based on an URI scheme.
In most cases these URLs are just normal HTML but they could also be a generated image (like a captcha) or a download link for a 700mb iso file - and there's no way to know be certain without checking out the header of the HTTP response from that URL.
Note: If you're writing your own crawler from scratch you're going to need good understanding of HTTP.
The first thing your crawler is going to see when gets an URL is the header, which contains a MIME content-type - it tells a browser/crawler how to process and open the data (is it HTML, normal text, .exe, etc). You'll probably want to download pages based on the MIME type instead of an URL scheme. The MIME type for HTML is text/html and you should check for that using the HTTP library you're using before downloading the rest of the content of an URL.
The Javascript problem
Same as above except that running javascript in the crawler/parser is pretty uncommon for simple projects and might create more problems than it solves. Why do you need Javascript?
A different solution
If you're willing to learn Python (or already know it) I suggest you look at Scrapy. It's a web crawling framework built similarly to the Django web framework. It's really easy to use and a lot of problems have already been solved so it could be a good starting point if you're trying to learn more about the technology.
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.