August 28, 2013

Sql Server allows for both Windows and Sql authentication, however, the Sql login is not enabled by default. The Sql login should be enabled if connection is needed to the database from outside a domain. A perfect scenario is when a database is in DMZ environment and connection is needed to it from web sites / services.

August 26, 2013

I worked on multi-site login solution where basically a user logs in first site - say site1.example.com - and then when the user browses to site2.example.com - the user is already logged in there. The way I initially dealt with it was to create a cookie in site1 that will be accessible in site2. Since, both site1 and site2 are sub-domains of the main domain, so, that sounded like a possible solution as long as we don't restrict the cookie by application or path.

August 25, 2013

Sometimes, when we connect to web services from within Visual Studio, I have noticed the error - 407 Error: Proxy Authentication Required while running webservice. This error is not anything to do code but basically that the system cannot connect to the remote WCF web service. To debug this issue, I usually try to navigate to the web service in the web browser - Internet Explorer. If the service is available then metadata page for the web service will appear. If not, the system cannot access the service. If it can connect via Internet Explorer, then add the following section in the web.config file. This setting allows Visual Studio to use the proxy setting from Internet Explorer to make any internet connection including connecting to the service.

August 22, 2013

How to get Client IP Address using Asp.Net

Client IP address might be sometimes useful depending on the use case. In different projects, the company might decide to release products based on IP address range, etc and it will be useful in those scenarios to get the ip address. However, if the product is a web application and it needs to get location of the user - then, HTML5's geolocation might be a better solution provided. I will discuss about HTML5 geolocation in a different post.

In asp.net, the Request object has access to various server variables including HTTP_X_FORWARDED_FOR and REMOTE_ADDR which are two important ones for retrieving client IP address. There is a method in the Request object as well - Request.UserHostAddress() - that can return the client IP. 

The problem with Request.UserHostAddress() is that this method only works if the user is not behind a proxy server. If the user is behind a proxy server, this method returns the IP address of the proxy server. In this situation, the IP address is stored in the server variable - HTTP_X_FORWARDED_FOR. This variable contains a list of comma separated IP addresses in the format client IP, proxy1 IP, proxy2 IP, ... It is important to note that if the original client IP is needed, then we need to get first IP address returned.

If the above variable - HTTP_X_FORWARDED_FOR - returns null, then a different server variable - REMOTE_ADDR - needs to be used to get the IP address. There is no difference between using the method - Request.UserHostAddress() - and the variable - REMOTE_ADDR. Here is a code snippet on how to get the IP address of the client.

Code Snippet
  1. public string GetUserIPAddress()
  2. {
  3.     string ip = null;
  4.  
  5.     //returns a comma separated IP addresses in the format client, proxy1, proxy2...
  6.     //the IP seen by system is the last proxy IP
  7.     ip = System.Web.HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
  8.  
  9.     if (ip == null)
  10.     {
  11.         ip = System.Web.HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
  12.         //or use the code below
  13.         //ip = System.Web.HttpContext.Current.Request.UserHostAddress;
  14.     }
  15.     else
  16.     {
  17.         ip = ip.Split(',')[0];
  18.     }
  19.     return ip;
  20. }

August 21, 2013

Lately I worked on a project that worked great on Visual Studio but upon deployment I kept get the error - "Operation is not valid due to the current state of the object". After doing some more tests, unfortunately, on production, I realised that the error is happening due to large data set that is returned from the database for the logged in user.

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Reference: Shahed Kazi at AspNetify.com