Even if you have used something for over a decade, you can learn about it

I was refactoring bits of code where someone clearly didn’t understand the benefits of enumerations, similar to this very contrived example:

using System;

namespace Demo
{
    // explicit equivalence of: 
    // public enum TrafficLight { Red, Yellow, Green };
    public enum TrafficLight { Red = 0, Yellow = 1, Green = 2 };

    public class Program
    {
        public static void Main()
        {
            // old code:
            Console.WriteLine(IntIsRedTrafficLight((int)TrafficLight.Red));
            Console.WriteLine(IntIsRedTrafficLight((int)TrafficLight.Yellow));
            Console.WriteLine(IntIsRedTrafficLight((int)TrafficLight.Green));
        }

        public static bool IntIsRedTrafficLight(int trafficLight)
        {
            return (trafficLight == (int)TrafficLight.Red);
        }
    }
}

The code was using way too many casts, and my goal was something as simple as this: Read the rest of this entry »

Small but useful, especially in countries that have something else than a dot (.) as decimal digit separator (all of the green countries: probably more than you’d thought).

The C# sourcecode is really simple use a NumberFormatInfo instance (or an instance of another class implementing IFormatProvider) in a Single.ToString call:

                float number = 3.1415;
                NumberFormatInfo numberFormatInfo = new NumberFormatInfo();
                numberFormatInfo.NumberDecimalSeparator = ".";
                numberFormatInfo.NumberGroupSeparator = string.Empty;
                string numberString = number.ToString(numberFormatInfo);

The classes implementing IFormatProvider are CultureInfo, DateTimeFormatInfo and NumberFormatInfo.

–jeroen

Let me start that you should store as little sensitive information as possible. But if you do, you should store it in a secure way. That’s why the .NET 2.0 introduced the SecureString class.

I won’t go into detail here, as the links below and the demo source do that much better than I can:

• Making strings more secure
• Data Protection API (DPAPI) part 1 and part 2
• Properly converting SecureString to string
• SecureStringToStringMarshaller
• How to use SecureString
• Comparing SecureString
• Credential Management
• PrepareConstrainedRegions explained
• ConstrainedExecutionRegion, SafeHandle and native handles explained
• ConstrainedExecutionRegion example
• Using Unsafe Code and Pointers

One warning: be very cautious when you convert a SecureString in a regular unsecure array of characters, string, or compare the unsecured content. To quote Fabio Pintos, everytime you do, a little village bursts on fire. When you access it in an insecure way, make sure it is pinned, clear and release the insecure memory as soon as possible.

The problem with a garbage collected environment like .NET is that strings live on the heap, and you can’t deterministically eliminate a string from memory like you could in deterministic environment like Delphi or C/C++.

Have fun with it!

–jeroen

Somehow this landed on my research list: TypedReference Structure (System) (together with __arglist, __makeref, __reftype and __refvalue)

Probably because of two reasons:

• it is the .NET equivalent of C-style varargs  (for instance also supported by Java, C++, python and other languags)  for variadic functions
• it can do fast things with value references without first boxing/unboxing them

–jeroen

More than a year ago, I wrote about .NET/C# – TEE filter that also runs on Windows (XP) Embedded.

Since then, I have made two changes to the code (which is below and in this CodePlex changeset):

1. using file modes FileAccess.Write and FileShare.Read, which allows you to load the output files with tools opening them in a read-only, deny none mode
2. optional flush of the files every CRLF pair, or every 4096 bytes

Read the rest of this entry »

MijnAlbum.nl is a popular site for storing and printing photos.

The UX of the site is far below what I’d like so I searched around for some scripts and wrote a bit of code for my own to make it easier.

First a few URL tricks for mijnalbum.nl (with the free demo album with Album ID TYEGMIMD):

1. Album URLs follow this pattern:
   http://www.mijnalbum.nl/Album=TYEGMIMD
   where the letters after Album= contain the Album ID.
2. When you click on a photo a new window opens with a URL like
   http://www.mijnalbum.nl/GroteFoto-3ANGJPWW.jpg
   where the letters after GroteFoto- contain the Photo ID and the .jpg extension.
   You don’t need to be logged in to download these photos.
3. The album page includes a frame with thumbnails that has a URL like
   http://www.mijnalbum.nl/index.php?m=albumview&a=2&key=TYEGMIMD&selectedfoto=3ANGJPWW
   but a bit of experimentation reveals it can be condensed into
   http://www.mijnalbum.nl/?m=albumview&a=2&key=TYEGMIMD
   where the letters after key= contain the Album ID.
4. The thumbnail frame contains photo’s that link to URLs like
   http://www.mijnalbum.nl/index.php?m=albumview&a=1&key=3ANGJPWW&album=TYEGMIMD
   that can be condensed into
   http://www.mijnalbum.nl/?m=albumview&a=1&key=3ANGJPWW&album=TYEGMIMD
   where you both need the Photo ID as key value, and Album ID as album value.
   The thumbnails are tiny, so not very convenient to browse.
5. Download URLs look like this
   http://www.mijnalbum.nl/index.php?m=download&a=10&key=TYEGMIMD
   which can be condensed into
   http://www.mijnalbum.nl/?m=download&a=10&key=TYEGMIMD
   but you need to be logged in to download other albums than the demo album.

The thumbnails frame contains two lists of the photos in the album. Given the demo album, it first contains a this section inside a bunch of JavaScript code:

thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-3ANGJPWW.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-6OKRE67M.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-4OSAXTJM.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-7MFJVO4F.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-YQ4BZ4AD.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-3LKQD6AG.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-O8RUL378.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-7TTFUUCG.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-L6SLLZHO.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-YLSWWFJI.jpg"));
thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-CFWOY8KK.jpg"));

and further in the page source a HTML table with HTML fragements like these:

        <a onclick="resetScrollNextImg();" onfocus="this.blur();" href="index.php?m=albumview&a=1&key=3ANGJPWW&album=TYEGMIMD" target="fotoframe">
 <img id="thumb-3ANGJPWW" style="margin-bottom: -3px;" title="Eendjes in de wei" src="http://www.mijnalbum.nl/MiniFoto-3ANGJPWW.jpg" alt="Eendjes in de wei" width="90" height="90" border="0" />
 </a>

The HTML fragment has more context (Picture ID in both the a and img tags, Picture description in the alt attribute of the img tag).

You need to parse either of the two tables, depending on what information you are interested in.

I was interested in the thumbnail URL, and the Photo IDs and GroteFoto download URLs because it is way easier to select photos that are bigger. Something like this list:

Thumbnail URL for Album TYEGMIMD
http://www.mijnalbum.nl/index.php?m=albumview&a=2&key=TYEGMIMD
Photo URLs for Album TYEGMIMD
http://www.mijnalbum.nl/GroteFoto-3ANGJPWW.jpg
http://www.mijnalbum.nl/GroteFoto-6OKRE67M.jpg
http://www.mijnalbum.nl/GroteFoto-4OSAXTJM.jpg
http://www.mijnalbum.nl/GroteFoto-7MFJVO4F.jpg
http://www.mijnalbum.nl/GroteFoto-YQ4BZ4AD.jpg
http://www.mijnalbum.nl/GroteFoto-3LKQD6AG.jpg
http://www.mijnalbum.nl/GroteFoto-O8RUL378.jpg
http://www.mijnalbum.nl/GroteFoto-7TTFUUCG.jpg
http://www.mijnalbum.nl/GroteFoto-L6SLLZHO.jpg
http://www.mijnalbum.nl/GroteFoto-YLSWWFJI.jpg
http://www.mijnalbum.nl/GroteFoto-CFWOY8KK.jpg

Since the thumbnail URL page is not xhtml, you have two options:

• Force the page to become XHTML by some library
• Use Regular Expressions

Though I am not a fan of using Regular Expressions for parsing general HTML, the thumbnail frame is generated in a very consistent way, so in this case I don’t mind using RegEx.

A complete console app is part of the bo.codeplex.com library.
This is the C# code I wrote as a base:

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace MijnAlbum.NL.Download.ConsoleApplication
{
    public class MijnAlbumNl
    {
        protected const string ThumbnailPrefix = "http://www.mijnalbum.nl/index.php?m=albumview&a=2&key=";
        protected const string BigJpegUrlMask = "http://www.mijnalbum.nl/GroteFoto-{0}.jpg";

        private static string DownloadString(string url)
        {
            var html = string.Empty;
            using (var webClient = new System.Net.WebClient())
            {
                html = webClient.DownloadString(url);
            }
            return html;
        }

        protected static string DownloadThumbnailsHtml(string AlbumID)
        {
            string url = GetThumbnailsUrl(AlbumID);
            string html = DownloadString(url);
            return html;
        }

        protected static string GetThumbnailsUrl(string AlbumID)
        {
            string url = ThumbnailPrefix + AlbumID;
            return url;
        }

        protected static List getPhotoIds(bool dumpGroups, string html)
        {
            List photoIds = new List();
            /* find strings like these:
            thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-3ANGJPWW.jpg"));
            thumbs.push(new Array("http://www.mijnalbum.nl/MiniFoto-6OKRE67M.jpg"));
                         * RegEx string:
            thumbs\.push\(new\ Array\("http://www.mijnalbum.nl/MiniFoto-(?.*?)\.jpg"\)\);
                         */
            // With @, you only have to escape the double quotes with another double quote: http://weblogs.asp.net/lorenh/archive/2004/09/30/236134.aspx
            const string RegExPattern = @"thumbs\.push\(new\ Array\(""http://www.mijnalbum.nl/MiniFoto-(?.*?)\.jpg\""\)\);";
            const string PhotoIdRegExCaptureGroupName = "PhotoId";
            //const string RegExReplacement = @"${PhotoId}";
            MatchCollection matchCollection = Regex.Matches(html, RegExPattern);
            // Matches uses lazy evaluation, so each match will be evaluated when it is accessed in the loop
            foreach (Match match in matchCollection)
            {
                Group positionIdGroup = match.Groups[PhotoIdRegExCaptureGroupName];
                if (dumpGroups)
                    Console.WriteLine(positionIdGroup.Value);
                photoIds.Add(positionIdGroup.Value);
            }
            return photoIds;
        }

        protected static string GetBigJpegUrl(string photoId)
        {
            string bigJpegUrl = string.Format(BigJpegUrlMask, photoId);
            return bigJpegUrl;
        }

    }

}

Note that others wrote some scripts too, so for instance Kees Hink  wrote on Foto’s downloaden van mijnalbum.nl and there is the MijnAlbumDownloader app.

Note 2: The free RegEx Expresso tool is very nice for building and testing Regular Expressions.

–jeroen

I’m a fan of ISO 8601, as it is a universal way of expressing dates and times (no more MDY confusion ).

I wrote about using ISO 8601 in batch-files and with Google Calendar before.

Now it is time to give you a simple C# example.

When you realize that XML uses ISO 8601 for their date and time formats, the .NET conversion is very easy:

using System;
using System.Xml;

public class Test
{
    public static void Main()
    {
        string Iso8601DateTime =
            XmlConvert.ToString(DateTime.Now, XmlDateTimeSerializationMode.Local);
        Console.WriteLine(Iso8601DateTime);
    }
}

I wrote about ideone.com before: it is an excellent place to run sample C# code (and other languages).

When running this on ideone.com, you can see their local server time in ISO 8601 format.
Cute

BTW: There are more ways to run your C# code online.

–jeroen

via: Simple example to show DateTime.Now in ISO 8601 format on Ideone.com | Online C# Compiler & Debugging Tool.