Using Rails’ Flash Messages with AJAX Requests

Have you ever wondered how to get access to the Ruby on Rails‘ flash message when performing a AJAX or restful web request?  You might hit yourself on the head when you discover how easy it is.  Simply append the flash message to the Response headers.  You could even wrap this in a helper, and using an after_filter to automatically add the header for you on every AJAX response.

class ApplicationController < ActionController::Base
after_filter :flash_headers

def flash_headers
  # This will discontinue execution if Rails detects that the request is not
  # from an AJAX request, i.e. the header wont be added for normal requests
  return unless request.xhr?

  # Add the appropriate flash messages to the header, add or remove as
  # needed, but I think you'll get the point
  response.headers['x-flash'] = flash[:error]  unless flash[:error].blank?
  response.headers['x-flash'] = flash[:notice]  unless flash[:notice].blank?
  response.headers['x-flash'] = flash[:warning]  unless flash[:warning].blank?

  # Stops the flash appearing when you next refresh the page
  flash.discard
end

And then you just read the header with whatever you happen to be reading it with. For completeness sake here is an example of how to read the header in JavaScript using Prototype:

 new Ajax.Request('/your/url', {
  onSuccess: function(response) {
    var flash = response.getHeader('x-flash);
    if (flash) alert(flash);
 }
});

Forget the UML Module for NetBeans!

A while ago, I wrote a blog post on how, with considerable effort, you can get a native UML NetBeans module up and running despite the NetBeans UML module being removed from the standard distribution.

I managed to get mine working, but there is a huge cost – Once you close the project (or the IDE) housing the diagram, you can never reopen it.  Out of pure determination desperation and perseverance I managed to get the diagram I needed, printed and done; but I can never open it and make adjustments.

Apparently, we’re all supposed to use SDE for NetBeans by Visual Paradigm now as the “official” replacement, but I tried it, and it was simply fail.  Proprietary and fail.

Fortunately, after taking a punt, I found a UML modelling tool which is not only more functional and better than the NetBean’s module was, but looks better too.  It even has the ability to create code from class diagrams (which you can obviously just cut and paste into your NetBeans IDE project of choice.  Its called ArgoUML.

ArgoUML is the leading open source UML modeling tool and includes support for all standard UML 1.4 diagrams. It runs on any Java platform and is available in ten languages.

I’ve used it a bit now, and I just love it.  I particularly like the way it can make recommendations on how to improve your diagram using its “critics” system.

It’s features boast:

  • All 9 UML 1.4 Diagrams supported
  • Platform Independent: Java 5+
  • Click and Go! with Java Web Start
  • Standard UML 1.4 Metamodel
  • UML Profile support with profiles provided
  • XMI Support
  • Export Diagrams as GIF, PNG, PS, EPS, PGML and SVG
  • Available in ten languages – EN, EN-GB, DE, ES, IT, RU, FR, NB, PT, ZH
  • Advanced diagram editing and Zoom
  • OCL Support
  • Forward Engineering
  • Reverse Engineering / Jar/class file Import
  • Cognitive Support
    • Reflection-in-action
      • Design Critics
      • Corrective Automations (partially implemented)
      • “To Do” List
      • User model (partially implemented)
    • Opportunistic Design
      • “To Do” List
      • Checklists
    • Comprehension and Problem Solving
      • Explorer Perspectives
      • Multiple, Overlapping Views

I haven’t yet worked out how to create object instances from my class diagrams yet, so I’m not sure if it just doesn’t support this or it’s user error, but in every other conceivable way, it seems to be an excellent UML modelling application for virtually every OS you can name.

Getting SSI to work in MAMP

It’s no secret that I adore my Mac, mostly because it just makes my life easier.  I enjoy the security of OSX, I love it’s responsiveness and I love that my operating system doesn’t punish me for installing applications and development stacks just to ‘play with them’.  A while ago, while looking for a stack that would let me quickly and effortlessly get Apache, MySQL and PHP5 working together without having to muss about with configs and the such, I discovered MAMP and frankly, I adored it instantly.  After a rather large download, it was effortless to install and running it was a cinch.  And better still, the server applications only run when you open the MAMP application and tell them to run, so that you dont loose vital system resources running services you dont need.

Additionally, my IDE of choice, NetBeans can integrate directly with MAMP, so that when you create (for sake of argument) a new PHP project and run it, it automatically puts the project files into the MAMP Apache directory (to be honest you do need to configure the path when you create the project, but its no big deal) making development painless and convenient.

But I did hit a snag recently when for a university assignment I was required to do a XHTML website using HTML Server Side Includes.  I was shocked when I ran my website and my SSI didnt work.

But there is a solution.

To make .shtml work, I deleted the comment-symbols ( # ) in the file http.conf (find it in /Applications/MAMP/conf/apache/ and at the time of writing was near lines 982:

# To parse .shtml files for server-side includes (SSI):
# (You will also need to add "Includes" to the "Options" directive.)
#
AddType text/html .shtml
AddOutputFilter INCLUDES .shtml

Download Microsoft .NET Framework 3.5 SP1 Standalone Full Redistributable Setup Installer

Many applications uses Microsoft .NET Framework 3.5 as development platform, and thus requires .NET Framework to be installed beforehand, else the installation will request to download and install .NET Framework from Internet. On offline system without Internet access or online server with slow downloading speed, the requirement to download setup files through web may hit the wall – a no go.

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Microsoft initially just provides a minimal size dotnetfx35setup.exe download which is a bootstrapper that will still need to download more files via Internet. For users who prefer to perform offline installation or install .NET Framework 3.5 SP1 without waiting for download to complete will have to download and save a copy of full complete standalone or redistributable Microsoft .NET Framework 3.5 SP1 setup installer, which is finally published by Microsoft.

Microsoft .NET Framework 3.5 SP1 (Service Pack 1) is a full cumulative update that contains many new features building incrementally upon .NET Framework 2.0, 3.0, 3.5, and includes cumulative servicing updates to the .NET Framework 2.0 and .NET Framework 3.0 subcomponents. See KB951847 for list of changes and fixed issues in the .NET Framework 3.5 Service Pack 1.

Download full package of Microsoft .NET Framework 3.5 SP1: dotnetfx35.exe (231 MB)

For known issues and release notes, refer to Microsoft .NET Framework 3.5 SP1 Readme.

Native UML Module for NetBeans

UPDATE: There is a more recent post regarding the Native UML module for NetBeans here.

I have been a long time user of NetBeans IDE. I really like the simplicity and how it is almost an all-purpose IDE for virtually any language you can think of.

However, I was horrified recently when I upgraded to version 6.8, to discover that the UML module was gone, and instead NetBeans insisting I use a third-party UML generator.  So I tried it, and hated it immediately.  I considered rolling back to an earlier version, but first I thought I would try a little voodoo.

I noticed that version 6.9 was released and so I downloaded it, and installed as per normal.  I then found this page (the 6.9 release candidate zip download page) which listed a file called ‘netbeans-6.9-201005312001-ml-uml.zip’.  Ah ha.  Since I am on OSX, I opened the package contents up from Applications, unzipped the uml.zip file and dropped the new UML directory into the installation directory.  I started up NetBeans and voila:

I tested the new project, and it worked like a treat (some people who tried various other hacks reported that even though the project appeared, there was issues saving/opening them).

I hope this works for you too, and of course make sure you backup any existing projects – dont come crying to me if you destroy your work trying to implement this!

Extracting Specific Date-time Components in Postgres

When programming, sometimes it’s useful to extract various time components from a Date-time field in SQL queries.  For example, you might want to filter the date field by, hour, or year (or both).  Fortunately, Postgres has a easy way to pull this data out within the query itself:

SELECT EXTRACT(hour FROM a_datetime_field) FROM a_table;

If the field was the value ‘4/5/2009 13:09:00’ then that above query would return “13” in the select.

In a stranger, practical example, I was moving a database from one server to another and for some unknown reason, all the dates in a table were fudged so that instead of being the year 2009, it was 142009, and the seconds were also stuffed up – the result being that any queries I ran against the table threw ADO.NET exceptions because the dates couldn’t be parsed properly.  I needed to run a query like this one to set things right again:

update atable
  set datetimeadded = cast( '2009-' || EXTRACT(month FROM datetimeadded) || '-' ||
    EXTRACT(day FROM datetimeadded) || ' ' || EXTRACT(hour FROM datetimeadded) || ':' ||
    EXTRACT(minute FROM datetimeadded) as timestamp),
  datetimeupdated =  cast('2009-' || EXTRACT(month FROM datetimeupdated) || '-' ||
    EXTRACT(day FROM datetimeupdated) || ' ' || EXTRACT(hour FROM datetimeupdated) || ':' ||
    EXTRACT(minute FROM datetimeupdated) as timestamp);

The casts are needed to get the update to cooperate, but basically this recreates the date time piece-by-piece based on the original date-time value.

Better way to get the Scheme, Host and Port from Uri Object in .Net

Recently I was working on a project where I needed to strip the scheme, host and port (if it wasn’t 80) from a Uri object. Obviously I could have used string concatenation to get the value I needed, but it just seemed so ghastly and inelegant. In frustration and annoyance that it wasn’t part of the standard Uri object definition, I asked a friend who gave me this little gem:

side effect of clomid

Uri uri = new Uri("http://localhost:6767/h/ello.php");
string url = new Uri(uri.AbsoluteUri).GetComponents(UriComponents.SchemeAndServer, UriFormat.Unescaped);

The string, ‘url’, will (in this example) hold the value “http://localhost:6767”. This works in .Net 2.0 and up, and with .Net 3.0, you could even create a static method extension to make it even easier.

Sometimes, Microsoft Gets it Right (The .NET Framework 4)

Parallel Programming are two words which are not nearly used enough by programmers today. I think this is partially due to the fact that most developers are answerable to management types who simply “want to get the job done”. It’s also highly susceptible to deadlocks, race conditions and other problems, which are somewhat more avoidable in traditional single-threaded-apartment model applications. The problem is, that we’ve reached a precipice in CPU architecture where CPUs are scaling out instead of up. In other words, instead of simply working harder and faster, they’re working smarter – executing many simultaneous operations.

The only problem with this is that applications need to be programmed to capitalize on this architecture – and making Multi-threaded applications easier is obviously on Microsoft’s mind with the announcements of features in the upcoming The .NET Framework 4.0.

One of the main the main features I am looking forward to is the Parallel class to easily thread simple loops. This Parallel class represents a significant advancement in simplistically managing loops.  The .Net 4.0 team assures us that “for many common scenarios, it just works, resulting in terrific speedups”.  A similar technique can be used to write parallel loops over iteration spaces of non-integral objects.

Parallel.For(0, N, i=>
  {
    DoWork(i);
  });

There are also overhauls to the ThreadPool class (which was in dire need of serious attention) and the inclusion of “Tasks” – simple generic types which assist developers in creating native IAsyncResult objects: this means that Task can be used as the core of a Begin/End implementation.  They’ve also really thought about these improvments, with easy and clear ways to cancel parallel operations, as well as a number of great ways to handle Exceptions within parallel blocks.

There are of course other advantages to the 4.0 Framework, but it’s the big emphasis on easing MTA (Multi-Threaded Apartment) model application development that’s got me excited.

Enjoy!

C# Levenshtein Distance (Difference Between 2 Strings)

If you want to match approximate strings with fuzzy logic, use the Levenshtein distance algorithm. Many projects need this logic, including programs such as spell-checkers, suggestion searches and plagiarism detectors.

In information theory and computer science, the Levenshtein distance is a metric for measuring the amount of difference between two sequences (i.e., the so called edit distance). The Levenshtein distance between two strings is given by the minimum number of operations needed to transform one string into the other, where an operation is an insertion, deletion, or substitution of a single character. A generalization of the Levenshtein distance (Damerau–Levenshtein distance) allows the transposition of two characters as an operation.

I needed to simply to measure the difference between two independant strings.  This was my saving grace, and the C# implementation I found:

using System;

/// 
/// Contains approximate string matching
/// 
static class LevenshteinDistance
{
    /// 
    /// Compute the distance between two strings.
    /// 
    ///The first of the two strings.
    ///The second of the two strings.
    /// The Levenshtein cost.
    public static int Compute(string s, string t)
    {
        int n = s.Length;
        int m = t.Length;
        int[,] d = new int[n + 1, m + 1];

        // Step 1
        if (n == 0)
        {
            return m;
        }

        if (m == 0)
        {
            return n;
        }

        // Step 2
        for (int i = 0; i <= n; d[i, 0] = i++)
        {
        }

        for (int j = 0; j <= m; d[0, j] = j++)
        {
        }

        // Step 3
        for (int i = 1; i <= n; i++)
        {
            //Step 4
            for (int j = 1; j <= m; j++)
            {
                // Step 5
                int cost = (t[j - 1] == s[i - 1]) ? 0 : 1;

                // Step 6
                d[i, j] = Math.Min(
                    Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1),
                    d[i - 1, j - 1] + cost);
            }
        }
        // Step 7
        return d[n, m];
    }
}

What’s the best Way for 2 Processes to Communicate in .Net?

While trawling the internet the other day, I came across this question, and thought it might be something that others might like to know.  The question was:

What’s the best (or maybe not the best — just good) way for two processes in the same machine to communicate, using .NET?

Actually the two processes in the app I’m working on aren’t even two different programs; they’re just two instances of the same EXE. I wanted to do something like a singleton app, but have it per user (meaning a Terminal Server or Citrix or App-V server with multiple users should be able to launch their own single copy of the app). If another instance is run by the same user, it should just delegate the task to the already running instance, then exit. Only one instance per user of the program should be running. So far I’ve done (thanks to StackOverflow) the part that detects whether an instance of the app is already running, using Mutex. But I need the second app instance to be able to send data to the first app instance.

I’m leaning towards using named pipes and WCF’s NetNamedPipeBinding for this, but if you have better ideas I’ll really appreciate it. Thanks 🙂

IPC is what I’ve used in the past for this. And it is supprisingly easy. .Net remoting is a good option but unfortunately it is a restricted option becasue you can’t for example use it on the CF.

Below is a copy of the class I use to perform Inter-process Communication, you can use it in conjuction with a MutEx if you wish, but it isnt necessary. As long as the “pMappedMemoryName” and “pNamedEventName” are the same in both processes, it should work just fine. I tried to make it as event driven as possible.

The class looks a little like this:

  public class IpcService {
    private IServiceContext mContext;
    const int maxLength = 1024;
    private Thread listenerThread;
    private readonly string mMappedMemoryName;
    private readonly string mNamedEventName;
    public event EventHandler IpcEvent;
    private readonly bool mPersistantListener;

    public IpcService(bool pPersistantListener)
      : this(pPersistantListener, "IpcData", "IpcSystemEvent") {
      ;
    }

    public IpcService(bool pPersistantListener, string pMappedMemoryName, string pNamedEventName) {
      mPersistantListener = pPersistantListener;
      mMappedMemoryName = pMappedMemoryName;
      mNamedEventName = pNamedEventName;
    }

    public void Init(IServiceContext pContext) {
      mContext = pContext;
      listenerThread = new Thread(new ThreadStart(listenUsingNamedEventsAndMemoryMappedFiles));
      listenerThread.IsBackground = !mPersistantListener;
      listenerThread.Start();
    }

    private void listenUsingNamedEventsAndMemoryMappedFiles() {
      IntPtr hWnd = EventsManagement.CreateEvent(true, false, mNamedEventName);
      while (listenerThread != null) {
        if (Event.WAITOBJECT == EventsManagement.WaitForSingleObject(hWnd, 1000)) {
          string data = Peek();
          EventsManagement.ResetEvent(hWnd);
          EventHandler handler = IpcEvent;
          if (handler != null) handler(this, new TextualEventArgs(data));
        }
      }
      EventsManagement.SetEvent(hWnd);
      Thread.Sleep(500);
      HandleManagement.CloseHandle(hWnd);
    }

    public void Poke(string format, params object[] args) {
      Poke(string.Format(format, args));
    }

    public void Poke(string somedata) {
      using (MemoryMappedFileStream fs = new MemoryMappedFileStream(mMappedMemoryName, maxLength, MemoryProtection.PageReadWrite)) {
        fs.MapViewToProcessMemory(0, maxLength);
        fs.Write(Encoding.ASCII.GetBytes(somedata + "\0"), 0, somedata.Length + 1);
      }
      IntPtr hWnd = EventsManagement.CreateEvent(true, false, mNamedEventName);
      EventsManagement.SetEvent(hWnd);
      Thread.Sleep(500);
      HandleManagement.CloseHandle(hWnd);
    }

    public string Peek() {
      byte[] buffer;
      using (MemoryMappedFileStream fs = new MemoryMappedFileStream(mMappedMemoryName, maxLength, MemoryProtection.PageReadWrite)) {
        fs.MapViewToProcessMemory(0, maxLength);
        buffer = new byte[maxLength];
        fs.Read(buffer, 0, buffer.Length);
      }
      string readdata = Encoding.ASCII.GetString(buffer, 0, buffer.Length);
      return readdata.Substring(0, readdata.IndexOf('\0'));
    }

    private bool mDisposed = false;

    public void Dispose() {
      if (!mDisposed) {
        mDisposed = true;
        if (listenerThread != null) {
          listenerThread.Abort();
          listenerThread = null;
        }
      }
    }

    ~IpcService() {
      Dispose();
    }

  }

Simply use the Poke method to write data, and the Peek method to read it, although I designed it to automatically fire an event when new data is available. In this way you can simply subscribe to the IpcEvent event and not have to worry about expensive and constant polls.  Enjoy.