Random Thoughts and Hints on Software Development : C#/dotNet fun

A Case Against Code Reviews

EldarM — Sat, 23 Aug 2008 09:17:00 GMT

I know, it sounds odd in the modern world where code reviews are almost like one of the Sacred Commandments, that is taken religiously and you could be burned at the stake for not respecting it. So, please, hold with me for a little heresy… No, I don’t argue that code reviews are valuable. It’s just everything in this world has cons and pros, and I’d like to discuss one unusual “con” of code reviews that usually does not come to light.

Anyway, imagine a small team very busy doing the work, that is, new features for your product. I stress that: everybody is busy. No kidding, real busy. And, surprise!, just like every other product, yours has bugs. And bugs are to be fixed, right? Right.

Now, how you’d fix a bug? There are generally, two philosophies about fixing the bugs. Well, may be more, and of course, there is that stupid “just fix the bug”, which completely ignores metaphysical side of the things we are discussing right now, but let me ignore this one for a while. So, these two approaches are patching vs. refactoring.

Now, what would you think is the right way to fix bugs? Admittedly, there are cases when patching is acceptable Examples? Quick Fix Engineering patches. Products, which are really done, and the less you touch them the better. Fixing embedded code of a space station passing a Jupiter, where every byte of the fix increases the chance of the whole fix to be corrupted and disable a multi-million irreplaceable spacecraft.

However, in most cases and in what’s considered “good engineering”, I strongly believe that refactoring is far superior to patching. It does not mean that every small bug requires complete rewrite of the product, not at all. But it means that you have to consider a bigger frame and not be afraid to change quite a bit, if necessary.

I know, I know, it sounds theoretical and questionable, so let me give you an example. Considering short size of an article, I’ll have to give a very simplified example, but quite a valid one nevertheless. Suppose, you have a method called DownloadCompletedInstant(), which is a callback at the moment, when some download is completed. In fact, all it does is to allow you to start downloading the next file. You find a bug, when one of our colleagues added to it something really really stupid, because he was confused with “Download completed” part of the name. In fact, it would not be stupid, if it would be in DownloadCompleted() callback instead of DownloadCompletedInstant() one. So, now you have two options:

1. Just move your colleague’s code from DownloadCompletedInstant() to DownloadCompleted()

2. Same as (1) plus renaming DownloadCompletedInstant() into ScheduleNextDownload(), hence avoiding a chance of future confusion.

So, what would you do? (2), clearly, right? However, there is a little problem. The renamed call is used in ten other files. So, although the change is microscopic, it affects much more files than a simple patch.

Now, your team is doing code reviews, so what’s the higher chance of getting it fast – posting a change with just a few lines of changes in a single file, or a changes with several dozen lines changed in a dozen or so files? And don’t forget, you want it fast. In part, because you want to fix the bug and get to the next, in part, because you don’t want the fix sitting on our computer and not being checked in. But! Everybody else is busy too. Everybody else has their own bugs. So, naturally, you would rather get a change with minimum affected lines just to get your colleagues do code review faster.

The result? The product gets a patch, not refactoring, and in a couple of months somebody will again misuse DownloadCompletedInstant() for something else, as bad as this time or even worse.

So, does it look right? Is it just me or is there a real problem somewhere here?

How to call C++ DLL from ASP.NET (C#) code?

EldarM — Fri, 22 Sep 2006 23:07:00 GMT

The problem: normally, you use DLLImport and P/Invoke. However, it only works if DLL is loaded. For normal program you can put it into the same folder as managed executable, and everything will be just fine. Not for ASP.NET, which is compiled into an obscure location, which you would not want to mess up with. Other places like System32 folder are also not a good choice. So, what can you do?

The solution: Actually, people already thought about this problem and found some solutions. See, for example, here. Some people even suggest to create the class dynamically, putting the correct DLLImport attribute value using the reflections. (See. here). However, the reality is much simpler. The only real problem is to ensure that DLL is loaded. One way to do that, is to create a special folder and put it into the PATH environment variable. If you don't like that, you can use the same solution, I did lately, simply load DLL ahead using LoadLibrary. Once it's in memory, the system will not look around on disk and will simply use it.

Code fragments (C#):

Declaration of LoadLibrary:

[DllImport("kernel32.dll")]
public static extern IntPtr LoadLibrary(string lpFileName);

[DllImport("kernel32.dll")]
public static extern IntPtr FreeLibrary(IntPtr library);

Declaration of your functions from C++ DLL:

[DllImport("SampleLib.dll", PreserveSig = true, CharSet = CharSet.Unicode)]
public static extern UInt32 DoStuff(...parameters...);

Loading DLL:

String DLLPath;
DLLPath = ... full path to your DLL...
IntPtr lib = LoadLibrary(DLLPath);
... now, if lib is equal zero, you failed...

Now you can call it:

UInt32 res = DoStuff(...);

And after you did what you wanted, don't forget to free it:

FreeLibrary(lib); // check HRESULT, if that bothers you

-----

Added 3/8/07: Thanks to PSP (see his comment below), an additional important point is uncovered: DLLImport seems to increase refcount on the library just like LoadLibrary() does. Hence, it looks like you will need to call FreeLibrary() twice. Very odd, but looks real. I wonder, who calls FreeLibrary() when LoadLibrary() is not used?

From the mail: how can I access database from C#

EldarM — Fri, 11 Aug 2006 22:32:00 GMT

_______________________________________
From: sandusergiu1984@....com [mailto:sandusergiu1984@....com]
Sent: Fri 8/11/2006 9:20 AM
To: Eldar Musayev
Subject: (Random Thoughts and Hints on Software Development) : C# Code
I thought how can I write a program in C# that searches a SQL Server database and outputs the results to the user? and couldn't give me please some ideas, or a fragment of code? Thanks a lot.
----------------------------------
This message was generated from a contact form at: http://blogs.msdn.com/eldar/default.aspx

Here it is. First, file Class1.cs (that’s a test driver):

using System;

namespace GetData
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Class1
{
  /// <summary>
  /// The main entry point for the application.
  /// </summary>
  [STAThread]
  static void Main(string[] args)
  {
   Console.WriteLine("Starting...");
   MyDataReader.InsertRow(73,"Гпфгпф");
   Console.WriteLine("Insert is done.");
   MyDataReader.ReadMyData();
   Console.WriteLine("Press any key to continiue...");
   Console.ReadLine();
   Console.WriteLine("... done.");
  }
}
}

Now the actual class that gets to the database:

using System;
using System.Data.SqlClient;

namespace GetData
{
/// <summary>
///
/// </summary>
public class MyDataReader
{
  public MyDataReader()
  {
  }

// SQLEXPRESS is used for
// the free SQL Express edition of SQL Server
  private static String myConnectionString = "Database=sample;Server=MyMachine\\SQLEXPRESS;Integrated Security=SSPI;";

  public static void InsertRow(int id, string str)
  {
   try
   {
    SqlConnection myConnection = new SqlConnection(myConnectionString);
    string myInsertQuery = "INSERT INTO SampleTable (id, str) Values('"+id.ToString()+"', '"+str+"')";
    SqlCommand myCommand = new SqlCommand(myInsertQuery);
    myCommand.Connection = myConnection;
    myConnection.Open();
    myCommand.ExecuteNonQuery();
    myCommand.Connection.Close();
   }
   catch (Exception e)
   {
    Console.WriteLine(e.ToString());
   }
  }

public static void ReadMyData()
  {
   string mySelectQuery = "SELECT id, str FROM SampleTable";
   SqlConnection myConnection = new SqlConnection(myConnectionString);
   SqlCommand myCommand = new SqlCommand(mySelectQuery,myConnection);
   myConnection.Open();
   SqlDataReader myReader = myCommand.ExecuteReader();
   try
   {
    while (myReader.Read())
    {
     Console.WriteLine(myReader.GetInt32(0) + ", " + myReader.GetString(1));
    }
   }
   finally
   {
    // always call Close when done reading.
    myReader.Close();
    // always call Close when done reading.
    myConnection.Close();
   }
  }
}
}

What you want is ReadMyData() method. Drop both files into the command-line C# program project in Visual Studio (Class1.cs instead of Class1.cs generated by Visual Studio), put the name of you machine into the connect string (and name of SQL Server instance too), compile, run. You are done. Of course, you need SQL Server installed, database sample, and table SampleTable with two fields – “id” and “str” in it.. You can use SQL Server on another machine, but see that it is configured to accept connections from non-local machine and use Windows authentications (that’s what SSPI stands fro in the connection string).

Good luck!

Impersonation and authentication with ASP.Net

EldarM — Mon, 12 Jun 2006 22:34:00 GMT

The task: make a web user authenticated (either with him directly providing user ID or password or through domain, if he is already logged in) and run ASP.Net code under his/her ID.

Frankly, that’s very easy, but I noticed that sometimes even very good developers don’t know how to do that. In short, impersonation element in web.config does the trick. If you know the rest, that’s it, you don't need the rest of this post.

Otherwise, let’s just go through the process. First, go to your IIS folder, usually C:\Inetpub\wwwroot, and create a folder for your application/webservice, say C:\Inetpub\wwwroot\Hello. You can do that in Windows Explorer. I will show an example with webservice,

In this folder you will need two files: web.config and Hello.asmx (assuming you want to call your webservice Hello).

Simple web.config looks like that:

<?xml version="1.0"?>

<system.web>

</system.web>

</configuration>

I have added debugging and set default language to C#, but that’s optional. Hello.asmx file is very simple:

<%@ WebService Language="C#" CodeBehind="~/App_Code/Hello.cs" Class="Hello" %>

Now, create a folder App_Code (C:\Inetpub\wwwroot\Hello\App_Code), that’s where the actual code traditionally lives, and create Hello.cs file, already referenced in Hello.asmx:

using System;

using System.Web;

using System.Web.Services;

using System.Web.Services.Protocols;

[WebService(Namespace = "http://hellomedear.org/test/namespace/")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

public class Hello : System.Web.Services.WebService

{

public Hello () {

}

[WebMethod]

public string HelloMeDear()

{

return "Hello, " + System.Security.Principal.WindowsIdentity.GetCurrent().Name.ToString() + "!";

}

This way it will return back the name of the current user, so we can track our progress. So, are we ready? Let’s try. Enter address http://yourmachine/hellome/hello.asmx in the browser. Oops... Error:

Server Error in '/' Application.

Parser Error

Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.

Parser Error Message: Could not create type 'Hello'.

Source Error:

Line 1:  <%@ WebService Language="C#" CodeBehind="~/App_Code/Hello.cs" Class="Hello" %>

Source File: /hellome/hello.asmx Line: 1

Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.42

Why? You forgot to tell IIS that there will be ASP.Net code in this folder. Go to Control Panel | Administrative Tools | Internet Information Services, then select default web site, open it and you’ll see your folder shown with a folder icon. Right-click on it, select Properties, and click on “Create” button near the grayed textbox Application name. The click OK, and the icon will become something mechanical. That’s what you want.

Try again. Now you should get the list of available methods, which in our case is simply HelloMeDear. Click on it, and if you do that from the same machine, you will see a button Invoke, which let’s you try the method.

Click on it. A new windows will open with the result:

<?xml version="1.0" encoding="utf-8" ?>

<string xmlns="http://hellomedear.org/test/namespace/">Hello, NT AUTHORITY\NETWORK SERVICE!</string>

That’s nice, but NT AUTHORITY\NETWORK SERVICE is not your ID. What happened?

Go again into properties of your folder in IIS management, pick Directory Security tab, and press Edit for Authentication and access control. See “Enable anonymous access” checked? That’s the problem. Even if you’ll get impersonation, it will be that automatic user marked in the textboxes next to it. Actually, let’s try it.

Go to your folder and open web.config file. First add

into <system.web> element. Try again:

<?xml version="1.0" encoding="utf-8" ?>

<string xmlns="http://hellomedear.org/test/namespace/">Hello, YOURMACHINE\IUSR_ YOURMACHINE!</string>

You’ve got that impersonated user. To avoid that, go again into IIS configuration for your folder, Directory Security, edit Authentication and access control, and uncheck Enable anonymous access, plus check checkbox Integrated Windows authentication. Try now:

<?xml version="1.0" encoding="utf-8" ?>

<string xmlns="http://hellomedear.org/test/namespace/">Hello, YOURMACHINE\yourID!</string>

You’ve got it! Actually, it’s nice to add also:

into your web.config file along with impersonation element. That’s it.

So, all steps in a short list:

Create IIS folder
Create web.config file (see below to get important element)
Create .asmx file (see above)
Create App_Code subfolder and create there .cs file (see above)
Go to Control Panel | Administrative Tools | Internet Information Services, open, select default website, select your folder under it, right click, Properties.
Create application (button on the left of Application name:)
Go to Directory Security tab, click on Edit for Authentication and access control
Uncheck Anonymous access, check Integrated Windows authentication
You are done. To try go to http://yourserver/hellome/hello.asmx

0x800736B1: Calling C++ code from ASP.Net (from .aspx pages or .asmx webservices)

EldarM — Thu, 08 Jun 2006 06:37:00 GMT

So, you have (or have to write) ASP.Net page or webservice, which should call native C++. Generally, it’s just extra work, but sometimes there is no other way, at least, no easier way.

Overall that’s fairly easy – use COM or P/Invoce, that’s it. However, sometimes you do so, and it does not work no matter what. A pretty common case is HRESULT code 0x800736B1 with a full message like "Unable to load DLL exception. This application has failed to start because the application configuration is incorrect. Reinstalling application may fix this problem." Very often case. And very puzzling. And not very well documented.

So now a big hint: that usually does not mean that your DLL is not found (although that’s possible), it usually means that your DLL depends on other DLLs that are missing. It usually happens when you develop on one machine, and deploy/run on another, especially if it has a different version of Windows or misses Visual Studio. Just check that everything needs is on the machine or link statically (although that will increase the size of your DLL).

P.S. Oh, I was just told that this is not the only thing that could go wrong... Sorry if I was not clear enough. What I wrote above, is something happening easily and likely, while overall list of what can go wrong is HUGE:

- permissions on DLL(s)
- code security
- wrong .config file
- wrong version of .Net
- P/Invoke problems/signature matches/encoding/preserving-not preserving signature...
- actual file location
- not being in a right place or Path if DLL is specified without a full path
- more..

Favorties.html

EldarM — Thu, 02 Mar 2006 21:43:00 GMT

Long long ago, when IE was still in version 1.0, most people, including me, used Netscape, where favorites were not a bunch of files hidden somewhere, but rather an HTML page. Few of my friends used to make this page a browser's start page -- quite convenient thing to do. I missed it, but got to writing a simple program that would generate it. Well, now, with .Net and C# it's so-o-o-o easy! So, I don't have that excuse anymore :-)

Here is a C# console application that generates such a file out of your Favorites folder. It finds Favorites automatically and drops the result in a folder from where you called it. You may call it from the StartUp to make sure it's updated each time you reboot. Use favorites.css (see the end of this post) to control how your favorites.html page will look like.

Merely compile this C# code (command line will do, or create a simple console C# application in Visual Studio, I used .Net 2.0) and have fun!

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace GrabFavorites
{
    class Program
    {
        static StreamWriter html;

        static String FindFavorites()
        {
            String s = System.Environment.GetEnvironmentVariable("USERPROFILE");
            s += "\\Favorites\\";
            return s;
        }

        static String GenLink(FileInfo file)
        {
            String url = "";
            char[] delim = new char[]{'='};

            StreamReader f = file.OpenText();
            while (!f.EndOfStream)
            {
                String line = f.ReadLine();
                String[] parts = line.Split(delim,2);
                if (parts.Length > 1 && parts[0].Equals("URL", StringComparison.InvariantCultureIgnoreCase))
                {
                    url = parts[1];
                    break;
                }
            }
            f.Close();
            String filename = file.Name;
            filename = filename.Remove(filename.Length - 4);
            return "<a href='"+url+"'>"+filename+"</a>";
        }

        static void WalkFavorites(String path, int level)
        {
            DirectoryInfo dir = new DirectoryInfo(path);
            if (!dir.Exists)
            {
                Console.WriteLine("Problems with directory '{0}'...", dir.FullName);
                return; // Oops... should break here...
            }

            FileInfo[] files = dir.GetFiles("*.url");
            foreach (FileInfo file in files)
            {
                html.WriteLine("<p class='line{0}'>{1}</p>", level, GenLink(file));
            }
            DirectoryInfo[] dirs = dir.GetDirectories();
            foreach (DirectoryInfo dr in dirs)
            {
                html.WriteLine("<p class='dir{0}'>{1}</p>",level,dr.Name);
                WalkFavorites(dr.FullName, level+1);
            }

        }

        static void Main(string[] args)
        {
            // Find Favorites
            String FavoritesPath = FindFavorites();
            html = new StreamWriter("favorites.html");

            html.WriteLine("<head><link rel='stylesheet' type='text/css' href='favorites.css' /></head>");
            html.WriteLine("<h1>Favorites</h1>");

            WalkFavorites(FavoritesPath,0);

            // Console.ReadKey();
            html.Close();
        }
    }
}

Favorites.css (change it the way you like, and drop into the same folder, where favorites.html is generated)

h1  { color: blue; }
.dir0        { font-size: 14pt; font-family: Arial; font-weight: bold; margin-top: 6;
               margin-bottom: 1 }
.dir1        { margin-left: 0.3in; text-indent: 0; font-size: 12pt; font-family: Arial; font-weight: bold; margin-top: 6;
               margin-bottom: 1 }
.dir2        { margin-left: 0.6in; text-indent: 0; font-size: 11pt; font-family: Arial; font-weight: bold; margin-top: 3;
               margin-bottom: 1 }
.dir3        { margin-left: 0.9in; text-indent: 0; font-size: 10pt; font-family: Arial; font-weight: bold; margin-top: 1;
               margin-bottom: 1 }
.dir4        { margin-left: 1.2in; text-indent: 0; font-size: 10pt; font-family: Arial; font-weight: bold; margin-top: 1;
               margin-bottom: 1 }
.dir5        { margin-left: 1.5in; text-indent: 0; font-size: 10pt; font-family: Arial; font-weight: bold; margin-top: 1;
               margin-bottom: 1 }
.dir6        { margin-left: 1.8in; text-indent: 0; font-size: 10pt; font-family: Arial; font-weight: bold; margin-top: 1;
               margin-bottom: 1 }
.dir7        { margin-left: 2.1in; text-indent: 0; font-size: 10pt; font-family: Arial; font-weight: bold; margin-top: 1;
               margin-bottom: 1 }
.line0        { margin-left: 0.3in; margin-top: 0; margin-bottom: 1 }
.line1        { margin-left: 0.6in; margin-top: 0; margin-bottom: 1 }
.line2        { margin-left: 0.9in; margin-top: 0; margin-bottom: 1 }
.line3        { margin-left: 1.2in; margin-top: 0; margin-bottom: 1 }
.line4        { margin-left: 1.5in; margin-top: 0; margin-bottom: 1 }
.line5        { margin-left: 1.8in; margin-top: 0; margin-bottom: 1 }
.line6        { margin-left: 2.1in; margin-top: 0; margin-bottom: 1 }
.line7        { margin-left: 2.4in; margin-top: 0; margin-bottom: 1 }