I'm using a C# WebClient to post login details to a page and read the all the results.
The page I am trying to load includes flash (which, in the browser, translates into HTML). I'm guessing it's flash to avoid being picked up by search engines???
The flash I am interested in is just text (not an image/video) etc and when I "View Selection Source" in firefox I do actually see the text, within HTML, that I want to see.
(Interestingly when I view the source for the whole page I do not see the text, within HTML, that I want to see. Could this be related?)
Currently after I have posted my login details, and loaded the HTML back, I see the page which does NOT show the flash HTML (as if I had viewed source for the whole page).
Thanks in advance,
Jim
PS: I should point out that the POST is actually working, my log in is successful.
Fiddler (or similar tool) is invaluable to track down screen-scraping problems like this. Using a normal browser and with fiddler active, look at all the requests being made as you go through the login and navigation process to get to the data you want. In between, you will likely see one or more things that your code is doing differently which the server is responding to and hence showing you different HTML than a real client.
The list of stuff below (think of it as "scraping 101") is what you want to look for. Most of the stuff below is probably stuff you're already doing, but I included everything for completeness.
In order to scrape effectively, you may need to deal with one or more of the following:
cookies and/or hidden fields. when you show up at any page on a site, you'll typically get a session cookie and/or hidden form field which (in a normal browser) would be propagated back to the server on all subsequent requests. You will likely also get a persistent cookie. On many sites, if a requests shows up without a proper cookie (or form field for sites using "cookieless sessions"), the site will redirect the user to a "no cookies" UI, a login page, or another undesirable location (from the scraper app's perspective). always make sure you capture the cookies set on the initial request and faithfully send them back to the server on subsequent requests, except if one of those subsequent requests changes a cookie (in which case propagate that new cookie instead).
authentication tokens a special case of above is forms-authentication cookies or hidden fields. make sure you're capturing the login token (usually a cookie) and sending it back.
POST vs. GET this is obvious, but make sure you're using the same HTTP method that a real browser does.
form fields (esp. hidden ones!) I'm sure you're doing this already, but make sure to send all form fields that a real browser does, not just the visible fields. make sure fields are HTML-encoded properly.
HTTP headers. you already checked this, but it may make sense to check again just to make sure the (non-cookie) headers are identical. I always start with the exact same headers and then start pulling out headers one by one, and only keep the ones that cause the request to fail or return bogus data. this approach simplifies your scraping code.
redirects. These can either come from the server, or from client script (e.g. "if user doesn't have flash plug-in loaded, redirect to a non-flash page"). See WebRequest: How to find a postal code using a WebRequest against this ContentType="application/xhtml+xml, text/xml, text/html; charset=utf-8"? for a crazy example of how redirection can trip up a screen-scraper. Note that if you're using .NET for scraping, you'll need to use HttpWebRequest (not WebClient) for redirect-dependent scraping, because by default WebClient doesn't provide a way for your code to attach cookies and headers to the second (post-redirect) request. See the thread above for more details.
sub-requests (frames, ajax, flash, etc.) - often, page elements (not the main HTTP requests) will end up fetching the data you want to scrape. you'll be able to figure this out by looking which HTTP response contains the text you want, and then working backwards until you find what on the page is actually making the request for that content. A few sites do really crazy things in sub-requests, like requesting compressed or encrypted text via ajax, and then using client-side script to decrypt it. if this is the case, you'll need to do a bit more work like reverse-engineering what the client script is doing.
ordering - this one is obvious: make HTTP requests in the same order that a browser client does. that doesn't mean you need to make every request (e.g. images). Typically you only need to make the requests which return text/html content type, unless the data you want is not in the HTML and is in an ajax/flash/etc. request.
(Interestingly when I view the source for the whole page I do not see the text, within HTML, that I want to see. Could this be related?)
This usually means that the discrepancy is caused by some DOM manipulations via javascript after the page has loaded. Try turning off javascript and see what it looks like.
Related
I'm trying to query a delivery companies consignment status page, though it uses ASP.NET viewstate which when not supplied as parameters it does not return a result.
How can I reliably either:
Not submit the values, or submit blank values
Submit a constant value that is reliable.
The resource in question is http:// 61.9.216.242 /xlcoads/contrack.aspx
I've tried using cURL and been successful but I don't know if I need to change viewstate etc.
I've also contacted the company without luck in having a more ReSTful version of the site available.
First of all you are trying to do something which doesn't support it, therefore there will not be any standard method for doing it.
__VIEWSTATE and __EVENTVALIDATION is used by .net to provide a sense of statefulness over stateless protocol(Tcp/ip), but it is easy to fool it.
Your friends will be Firefox and firebug, Submit 4-5 different request and see the sent data in firebug, you will be able to figure out which datas are constant and which changes. When figured out, use webrequest to get the url data, then extract view state and other datas as needed make another webrequest to submit the modified data with the search string.
and yes I use this method for a site with the same problem.
I am attempting to scrape a website which has some kind of flash plugin which is loading data after i retrieve the html. The following object is received in the page
<OBJECT classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0" WIDTH="250" HEIGHT="20" id="Preloader"><PARAM NAME="movie" VALUE="/images/preloader.swf">
<PARAM NAME="quality" VALUE="high">
<PARAM NAME**strong text**="bgcolor" VALUE="#FFFFFF"><EMBED src="/images/preloader.swf" quality="high" bgcolor="#FFFFFF" WIDTH="250" HEIGHT="20" NAME="Preloader" ALIGN="" TYPE="application/x-shockwave-flash" PLUGINSPAGE="http://www.macromedia.com/go/getflashplayer"></EMBED></OBJECT>
Ive attempted to locate the data being received on wireshark but no luck. My knowledge of this flash plugin or how it works is nil. Im guessing the worst case scenario that I will not be able to do this.
HttpWebRequest mainRequest = (HttpWebRequest)(WebRequest.Create(URL));
mainRequest.Method = "GET";
mainRequest.Proxy = null;
WebResponse mainResponse = mainRequest.GetResponse();
StreamReader dataReader = new StreamReader(mainResponse.GetResponseStream(), System.Text.Encoding.UTF8);
string data = dataReader.ReadToEnd();
dataReader.Close();
mainResponse.Close();
return data;
Does anyone know a way I can receive this data or make the webresponse wait for the data to be injected to the html before it is received. Any help would be greatly appreciated.
UPDATE:
It seems I may have jumped the gun a little with the flash object. I think this is just a loading animation while the table populates. I've been using fiddler to see what is going on. The page is returned after a request with a loading div and the flash object contained inside. A few seconds later when the data is ready another page is returned with the data. From what I can rememebr (im not at home so cannot confirm right now) the new page has the same request header as the original. Theres no json or ajax data in fiddler. Theres no script on the client to cause a refresh that I can see. I do not understand what is causing this to update.
Ive briefly looked at the web browser object but I imagine this will be quite a performance hit when im scraping about 200 pages, currently taking a minute or so. I will try the amf viewer later to confirm that the flash object is not the source of the update.
Im guessing that the server is causing this page to be resent when it has the table ready.
If the server is finding the loading div and replacing this with the table of data, would this cause the whole page to be resent? Or wouldnt this show up in ajax/json data? If it is the server resending the data, how can I keep the response open until it is ready to send the new page?
Thanks. JM.
If the content is being loaded dynamically into the Flash movie it's very likely occurring over a standard HTTP request. Wire Shark may be a little overkill for detecting something like this. I'd recommend using a utility that will capture HTTP, such as Charles, HttpFox, or screen-scraper. Using one of those tools, watch the HTTP requests that occur while the content is loading. Once you determine which request it is it's likely you can just replicate it in your code.
That said, I've also seen cases (though not very common) where the data loaded into the Flash movie is done with a binary protocol, which makes things a little more difficult. AMF is often the protocol used in these cases. Charles proxy will detect this protocol, so that may be the tool to use in this case. A while back I wrote a blog post on extracting data that's delivered via AMF. It deals with a Java library, but you may be able to find something equivalent in .NET.
You won't be able to do that with a plain HttpWebRequest because the Flash content isn't running. The response you get back is just the HTML. It requires a browser (or a browser-like object) to actually execute, load that object, and pull down the content. I know there are libraries for executing Javascript, but I don't know of anything that will let you run a Flash plugin outside of a browser.
You might be better off using a WebBrowser object. But even if it will execute the Flash content (I honestly don't know if it will), you might not be able to access it. You'll have to look at the DOM and see.
Use Firebug and / or TamperData, load your page with flash as usual, and wait until Flash makes the HTTP POST/GET for getting the data.
Flash has three options to get data:
Sockets
HTTP GET
HTTP POST
You can fool this thing any day. Just have to make sure your request contains all this little things:
Method (GET or POST)
Cookies
Form Values (why? session state, for example)
URL Referrer
User Agent
Custom HTTP-Headers? (some guys might put this in the HTTP request so no one can "fool" the server)
This could make difference of having a response with data a default html error page.
One last thing:
If the content is delivered via HTTPS, then, don't worry, it's just an extra layer somewhere but still possible.
If the content is delivered via sockets, then forget it.
Similar questions have been asked about the nature of when to use POST and when to use GET in an AJAX request
Here:
What are the advantages of using a GET request over a POST request?
and here: GET vs. POST ajax requests: When and how to use either?
However, I want to make it clear that that is not exactly what I am asking. I get idempotence, sensitive data, the ability for browsers to be able to try again in the event of an error, and the ability for the browser to be able to cache query string data.
My real scenario is such that I want to prevent my users from being able to simply enter in the URL to my "Compute.cshtml" file (i.e. the file on the server that my jQuery $.ajax function posts to).
I am in a WebMatrix C#.net web-pages environment and I have tried to precede the file name with an underscore (_), but apparently an AJAX request falls under the same criteria that this underscore was designed to prevent the display of and it, of course, breaks the request.
So if I use POST I can simply use this logic:
if (!IsPost) //if this is not a post...
{
Response.Redirect("~/") //...redirect back to home page.
}
If I use GET, I suppose I can send additional data like a string containing the value "AccessGranted" and check it on the other side to see if it equals this value and redirect if not, but this could be easily duplicated through typing in the address bar (not that the data is sensitive on the other side, but...).
Anyway, I suppose I am asking if it is okay to always use POST to handle this logic or what the appropriate way to handle my situation is in regards to using GET or POST with AJAX in a WebMatrix C#.net web-pages environment.
My advice is, don't try to stop them. It's harmless.
You won't have direct links to it, so it won't really come up. (You might want your robots.txt to exclude the whole /api directory, for Google's sake).
It is data they have access to anyway (otherwise you need server-side trimming), so you can't be exposing anything dangerous or sensitive.
The advantages in using GETs for GET-like requests are many, as you linked to (caching, semantics, etc)
So what's the harm in having that url be accessible via direct browser entry? They can POST directly too, if they're crafty enough, using Fiddler "compose" for example. And having the GETs be accessible via url is useful for debugging.
EDIT: See sites like http://www.robotstxt.org/orig.html for lots of details, but a robots.txt that excluded search engines from your web services directory called /api would look like this:
User-agent: *
Disallow: /api/
Similar to IsPost, you can use IsAjax to determine whether the request was initiated by the XmlHttpRequest object in most browsers.
if(!IsAjax){
Response.Redirect("~/WhatDoYouThinkYoureDoing.cshtml");
}
It checks the request to see if it has an X-Requested-With header with the value of XmlHttpRequest, or if there is an item in the Request object with the key X-Requested-With that has a value of XmlHttpRequest.
One way to detect a direct AJAX call is to check for the presence of the http_referer header. Directly typed URLs won't generate a referrer, but you still won't be able to differentiate the call from a simple anchor link.
(Just keep in mind that some browsers don't generate the header for XHR requests.)
I've come across an issue while I was writing a utility to scrape a web page.
I'm sending POST requests to retrieve data, I mimic the behavior of the web I'm scrapping (According to info collected with fiddler).
I've been able to automatically replace all params on my POST except VIEWSTATE.
my guess is that the web is performing some logic according to the given VIEWSTATE, and that's why I'm not getting the expected result (I tried entering the value fiddler gives inside VIEWSTATE and then I do get the expected results, however I want to automate this process)
Is there a way I can edit a VIEWSTATE string without damaging it?
I tried decoding & encoding back using base64 (and finally URLEncode before POST action), couldn't keep it valid.
The viewstate is probably encrypted.
http://msdn.microsoft.com/en-us/library/aa479501.aspx
The viewstate should be encrypted, anyway. It's a protection aganst XSRF attacks of the type you seem to be trying to do :-)
The bottom line is the ViewState you send back must be the same as the viewstate the server sent to you. That's pretty much what it is for. In other words, to do what you are trying to do you have to keep a copy of the viewstate the server sent you, and send the same viewstate back. The server will then send you a new viewstate, which you must submit with your next request, and so on.
You can use the same serializator asp.net uses. I think it is a class named HiddenFieldPageStatePersister.
http://msdn.microsoft.com/en-us/library/system.web.ui.hiddenfieldpagestatepersister.aspx
Hope it helps
I have an idea for an App that would really help me out in work but I'm not sure if it's possible.
I want to run a C# desktop application that will ask for a value. When a value is supplied, the application will open a browswer, go to a webpage and add the value into a form on an online website. The form is then submitted and a new page is loaded that contains a table of results. I then want to extract the table of results from the page source and write code to parse the result values.
It is not important that the user see's this happen in an actual browser. In other words if there's a way to do it by reading HTTP requests then thats great.
The biggest problem I have is getting the values into the form and then retrieving the page source after the form is submitted and the next page loads.
Any help really appreciated.
Thanks
Provided that you're only using this in a legal context:
Usually, web forms are sent via POST request to the web server, specifically some script that handles it. You can look at the HTML code for the form's page and find out the destination for the form (form's action).
You can then use a HttpWebRequest in C# to "pretend you are the form", sending a POST request with all the required parameters (adding them to the HTTP header).
As a result you will get the source code of the destination page as it would be sent to the browser. You can parse this.
This is definitely possible and you don't need to use an actual web browser for this. You can simply use a System.Net.WebClient to send your HTTP request and get an HTTP response.
I suggest to use wireshark (or you can use Firefox + Firebug) it allows you to see HTTP requests and responses. By looking at the HTTP traffic you can see exactly how you should pass your HTTP request and which parameters you should be setting.
You don't need to involve the browser with this. WebClient should do all that you require. You'll need to see what's actually being posted when you submit the form with the browser, and then you should be able to make a POST request using the WebClient and retrieve the resulting page as a string.
The docs for the WebClient constructor have a nice example.
See e.g. this question for some pointers on at least the data retrieval side. You're going to know a lot more about the http protocol before you're done with this...
Why would you do this through web pages if you don't even want the user to do anything?
Web pages are purely for interaction with users, if you simply want data transfer, use WCF.
#Brian using Wireshark will result in a very angry network manager, make sure you are actually allowed to use it.