The program has a black list, it contains a list of sites. When the user opens the site in IE (Firefox, Opera, Chrome) he should get an error. (For example 404).
How can I do? It is advisable not writing to the file HOSTS.
Language C#.
What you are describing is a Proxy server:
http://www.squid-cache.org/
The concept behind what you're trying to do is monitoring port 80 outgoing traffic and block any requests addressed to sites/ips contained in the black list.
It's kind of complex posting for you the whole code here.
Regardless, this kind of operation is best suited to a network firewall filter than to a custom C# app that runs on the client.
Related
I serve pictures via WCF according to this tutorial:
https://delog.wordpress.com/2013/07/19/serving-static-web-content-using-wcf/
It works well on localhost but not always works on production: www.findacruise.net
Chrome shows errors like these:
http://79.143.179.248:8005/wwwservice/content/2//su52ch15.zhz.jpg Failed to load resource: net::ERR_CONNECTION_TIMED_OUT
On the same laptop it works at home but does not work at workplace. So I am guessing it does not have anything to do with WCF service itself. May be "Same origin policy" issue?
Thanks!
As discussed in comments, the issue appears to be that you whitelisted the IP address of your home browser, and your site.
However, as discussed, you also need to whitelist the internet at large (or, more sensibly, remove whitelist blocking entirely) in order to
Telnet is a useful tool for diagnosing these sorts of issues as it removes the HTTP layer entirely, and let's you focus on the underlying network issue.
Please note - I suggest you read up on the OSI Model of networking - it defines 7 layers from the physical transport layer (like a fiber optic cable) to the application layer (like HTTP) which provides a useful mental model for thinking about issues like this. Always try and isolate your problem to the lowest level at which it manifests :)
I want to check which web sites is open in browsers ( IE, Firefox, Chrome ) to write a program in C# which can block web site which is in list of forbidden web site. Is there some API of browsers?
The better solution can be to write a TCP/IP filter, like most firewalls do.
UPD: this topic can be relevant: How do I hook the TCP stack in Windows to sniff and modify packets?
There is no generic "browser API" that allows access to this kind of information across all browsers.
I'm pretty sure the idea of doing this by accessing the browsers is doomed from the start. It is going to be almost impossible to implement, require frequent updates, and always extremely easy to circumvent (there are dozens and dozens of browsers that your program will not know.).
The only reliable way is to filter traffic on network level. I would recommend looking into using an existing proxy server or TCP filtering program. There are several Open Source ones that I'm sure you can use as a basis to rewrite or hook into.
The easier solution is to write an http listener that logs the requests.
Fiddler2 is one of these, you can check it out. it logs all incomming and outcomming http content.
I have code on my server which works very well. It must crawl a few pages on remote sites to work properly. I know some users may want to abuse my site so instead of running the code which uses webclient and HttpRequest i would like it to run on client side so if it is abused the user may have his IP blacklisted instead of my server. How might i run this code client side? I am thinking silverlight may be a solution but i know nothing about it.
Yes, Silverlight is the solution that lets you run a limited subset of .NET code on client's machine. Just google for silverlight limitations to get more information about what's not available.
I don't know what is the scenario you're trying to implement, and whether you need real-time results, but I guess caching the crawl results could be a good idea?
In case you're after web scraping, you should be able to find a couple of JavaScript frameworks that for you.
I think your options here are Silverlight or somesort of desktop app
Unless maybe there is a jquery library or other client scripting language that can do same things
That's an interesting request (no pun). If you do use Silverlight then maybe instead of porting your logic to it, create a simple Proxy class in it that receives Requests from your server app and shuttles it forward for the dirty work. Same with the incoming Responses: have your Silverlight proxy send it back to the server app.
This way you have the option of running your server app through the Silverlight proxy in some instances, and on its own (with no proxy) in other scenarios. The silverlight plugin should provide a consistent API to program against no matter which browser it's running in.
If using a proxy solution in the web browser, you might even be able to skip Silverlight altogether and use JavaScript/AJAX calls. Of course this kind of thing is usually fraught with browser compatibility issues and it would be an obscure push/pull implementation for sure, but I think JavaScript can access domains and URLs and (in some cases of usage) not be restricted to the one it originated from.
If Silverlight security stands in the way you might look into other kinds of programmable (turing complete) browser plugins like Java, Flash, etc. If memory serves correct, for the Java plugin, it can only communicate over the network with the domain it originated from. This kind of security is too restrictive for your crawling needs.
On the client machine I need to be able to somehow detect which sites the current user are looking at right now.
I know the base URL of the sharepoint app, say sharepoint.thecompany.net but how the hack do I get the last requested url from the server?
I have hit a dead stop when trying to iterate the current processes and the casting the iexplorer process to something I can work with, I just don't know which kind of object to cast the process to :-(
I hope to implement this logic in a C# assembly what should run on the client box.
Any other approach that might work?
Thanks in advance
WatiN will allow you to attach to IE instances and get the current url from them. It will also allow you to do the same with Firefox instances.
It might be more efficient however to try to get requested urls at the network level using a wireshark type concept where you are just listening to http traffic on the computer and keeping track of the urls but a solution like that is a bit over my head.
EDIT: I came across this while looking for a solution: http://www.codeproject.com/KB/IP/networkmonitor.aspx
From what I can see I would think you could adapt the monitoring code to monitor and look for http request packets and parse the headers for the url information you need.
I hope someone can guide me as I'm stuck... I need to write an emergency broadcast system that notifies workstations of an emergency and pops up a little message at the bottom of the user's screen. This seems simple enough but there are about 4000 workstations over multiple subnets. The system needs to be almost realtime, lightweight and easy to deploy as a windows service.
The problem started when I discovered that the routers do not forward UDP broadcast packets x.x.x.255. Later I made a simple test hook in VB6 to catch net send messages but even those didn't pass the routers. I also wrote a simple packet sniffer to filter packets only to find that the network packets never reached the intended destination.
Then I took a look and explored using MSMQ over HTTP, but this required IIS to be installed on the target workstation. Since there are so many workstations it would be a major security concern.
Right now I've finished a web service with asynchronous callback that sends an event to subscribers. It works perfectly on a small scale but once there are more than 15 subscribers performance degrades considerably. Polling a server isn't really an option because of the load it will generate on the server (plus I've tried it too)
I need your help to guide me as to what technology to use. has anyone used the comet way with so many clients or should I look at WCF?
I'm using Visual C# 2005. Please help me out of this predicament.
Thanks
Consider using WCF callbacks mechanism and events. There is good introduction by Juval Lowy.
Another pattern is to implement blocking web-service calls. This is how GMail chat works, for example. However, you will have to deal with sessions and timeouts here. It works when clients are behind NATs and Firewalls and not reachable directly. But it may be too complicated for simple alert within intranet.
This is exactly what Multicast was designed for.
A normal network broadcast (by definition) stays on the local subnet, and will not be forwarded through routers.
Multicast transmissions on the other hand can have various scopes, ranging from subnet local, through site local, even to global. All you need is for the various routers connecting your subnets together to be multicast aware.
This problem i think is best solved with socket.
Open a connection to the server, and keep it open.
Could you have a slave server in each subnet that was responsible for distributing the messages to all the clients in the subnet?
Then you could have just the slaves attached to the central server where the messages are initiated.
I think some of you are vastly overthinking this. There is already a service built into every version of Windows that provides this exact functionality! It is called the Messenger service. All you have to do is ensure that this service is enabled and running on all clients.
(Although you didn't specify in the question, I'm assuming from your choices of technology that the client population of this network is all Windows).
You can send messages using this facility from the command line using something like this:
NET SEND computername "This is a test message"
The NET SEND command also has options to send by Windows domain, or to specific users by name regardless of where they are logged in, or to every system that is connected to a particular Windows server. Those options should let you easily avoid the subnet issue, particularly if you use domain-based security on your network. (You may need the "Alerter" service enabled on certain servers if you are sending messages through the server and not directly to the clients).
The programmatic version of this is an API called NetMessageBufferSend() which is pretty straightforward. A quick scan of P/Invoke.net finds a page for this API that supplies not only the definitions you need to call out to the API, but also a C# sample program!
You shouldn't need to write any client-side code at all. Probably the most involved thing will be figuring out the best set of calls to this API that will get complete coverage of the network in your configuration.
ETA: I just noticed that the Messenger service and this API are completely gone in Windows Vista. Very odd of Microsoft to completely remove functionality like this. It appears that this vendor has a compatible replacement for Vista.