'<name>' is ambiguous in the namespace '<namespace>'

This error has the following error code Error ID: BC30560.

One thing you could easily try is to change the value of the batch attribute in the <compilation> element of your Web.config file to false

<compilation defaultLanguage="vb" debug="false" batch="false">

I recently had the ”<name>’ is ambiguous in the namespace’ error appear in a very popular web site that has about 2 and a half million page views per month. It appeared only in the production server, not in the development or the testing server and nothing could make the error go away.
Changing this setting, allowed the application to have a faster first load (by not loading all objects of its dll at once) and made the error go away.

This post gathers a few things I ran into the last few weeks and thought it would be fun to share it with you.

Interesting

Programmer Interrupted
An article that describes how a programmer behaves when he is been interrupted when coding. It is an analysis based on 10,000 programming sessions recorded from 86 programmers using Eclipse and Visual Studio and a survey of 414 programmers.

The 10 rules of a Zen programmer
Programmers can be a weird breed. The old Zen-masters already knew before hundreds of years, how today programmers should work.

JS Complexity
How does your js code score?

More Code, More Problems
Learn languages, not frameworks.
Build small things.
Less code is better than more.

X-Surface: Don’t believe everything you read.
The games industry is the only one I can think of that will quite happily publish guesswork as news. So-called ‘analysts’ are no different – they make money by guessing. They’re about as much use as a ‘source’ as I am.

Useful

The Big Bad-ass list
We all love Bootstrap, and has become the norm in web design. It has created its own ecosystem, and the above link contains 267 resources for it.

Single page apps in depth
This free book is focusing on discussing patterns, implementation choices and decent practices while writing a single page app.

Twitter

From @rstevens
Water is coffee with javascript turned off.
From @_astewart
“Boy, I really hope this web service returns XML” – Nobody ever.
From @BrettDruck
Fashion savvy people probably look at my outfit the same way I look at a person who opens their laptop and has the ask toolbar installed.

<configuration> 
  <system.web> 
    <pages validateRequest="false" /> 
  </system.web> 
</configuration>

In .NET 4.0, you need to change one more property.

<configuration> 
  <system.web> 
    <pages validateRequest="false" />  
    <httpRuntime requestValidationMode="2.0"/>
  </system.web> 
</configuration>

If you want to apply this setting to a specific page, you can set it in the page directive of your .aspx file.

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Example.aspx.cs" 
                    Inherits="Example.Example" ValidateRequest="false" %>

In case your web application is an ASP.NET MVC project and want to disable page validation for a specific view, you can set this property to its controller.

[Post, ValidateInput(false)]
public ActionResult Edit(...) {
    ...
}

In MVC, you can actually declare which properties of your model you want to exclude from the validation process.

[HttpPost, ValidateInput(true, Exclude = "YourFieldName")]
public virtual ActionResult Edit(...)
{
    ...
}

Another approach is to set at the property of the Model to allow HTML content.

[AllowHtml]
public string Description { get; set; }

Going back to Web Forms, if you want to allow HTML / JavaScript for a specific field, there is no direct way to do it. A nice trick you could do, is to encode the HTML in the client side and then decode it in the server side.
The client side code

// The event to escape the data and store in our HiddenField
jQuery('.allow_html textarea').blur(function () {
    jQuery(jQuery(this).parent()).find('input[type="hidden"]').val(escape(jQuery(this).val()));
});
 
// The code to unescape the code and set it in our textbox
jQuery('.allow_html textarea').each(function(idx, item) {
    var value = jQuery(jQuery(item).parent()).find('input[type="hidden"]').val();
    jQuery(item).val(unescape(value));
});

The server side code

// encode the data
HtmlCodeHiddenField.Value = Uri.EscapeDataString(EscapedHtml);
// decode the data
string myHtml = Uri.UnescapeDataString(HtmlCodeHiddenField.Value);

If you want to read more about this subject, read this article from Stack Overflow.

In both cases we perform a web request and get back an xml file with the video’s data. Then our function parses the xml and loads the data to the object properties.

class Video
{
  public const string ytKey = "";
  public int Duration { get; set; }
  public string Title { get; set; }
  public string ThumbUrl { get; set; }
  public string BigThumbUrl { get; set; }
  public string Description { get; set; }
  public string VideoDuration { get; set; }
  public string Url { get; set; }
  public DateTime UploadDate { get; set; }
 
  public Video()
  {
  }
 
  public bool YouTubeImport(string VideoID)
  {
    try {
      int VideoDuration = -1;
 
      Net.WebClient myDownloader = new Net.WebClient();
      myDownloader.Encoding = System.Text.Encoding.UTF8;
 
      string myData = myDownloader.DownloadString("http://gdata.youtube.com/feeds/api/videos/" + VideoID + "?key=" + ytKey);
      System.Xml.XmlDocument myXml = new System.Xml.XmlDocument();
      myXml.LoadXml(myData);
      System.Xml.XmlElement myNode = myXml.GetElementsByTagName("entry")(0);
 
      Title = myNode.GetElementsByTagName("title")(0).InnerText;
      ThumbUrl = "http://i.ytimg.com/vi/" + VideoID + "/default.jpg";
      BigThumbUrl = "http://i.ytimg.com/vi/" + VideoID + "/mqdefault.jpg";
      Description = myNode.GetElementsByTagName("content")(0).InnerText.Replace(Strings.Chr(10), "<br />").Replace(Strings.Chr(13), "");
      UploadDate = Convert.ToDateTime(myNode.GetElementsByTagName("published")(0).InnerText);
      VideoDuration = myXml.GetElementsByTagName("yt:duration")(0).Attributes("seconds").Value;
      Duration = Convert.ToInt32(VideoDuration / 60).ToString("00") + ":" + Convert.ToInt32(VideoDuration % 60).ToString("00");
      Url = "http://www.youtube.com/watch?v=" + VideoID;
 
      return true;
    } catch (Exception ex) {
      return false;
    }
  }
 
  public bool VimeoImport(string VideoID)
  {
    try {
      int VideoDuration = -1;
 
      Net.WebClient myDownloader = new Net.WebClient();
      myDownloader.Encoding = System.Text.Encoding.UTF8;
 
      string myData = myDownloader.DownloadString("http://vimeo.com/api/v2/video/" + VideoID + ".xml");
      System.Xml.XmlDocument myXml = new System.Xml.XmlDocument();
      myXml.LoadXml(myData);
      System.Xml.XmlElement myNode = myXml.GetElementsByTagName("videos")(0);
 
      Title = myNode.GetElementsByTagName("title")(0).InnerText;
      ThumbUrl = myNode.GetElementsByTagName("thumbnail_medium")(0).InnerText;
      PlayerImage = myNode.GetElementsByTagName("thumbnail_large")(0).InnerText;
      Description = myNode.GetElementsByTagName("description")(0).InnerText;
      UploadDate = Convert.ToDateTime(myNode.GetElementsByTagName("upload_date")(0).InnerText);
      VideoDuration = myXml.GetElementsByTagName("duration")(0).InnerText;
      Duration = Convert.ToInt32(VideoDuration / 60).ToString("00") + ":" + Convert.ToInt32(VideoDuration % 60).ToString("00");
      FileName = "http://vimeo.com/" + VideoID;
      EmbedCode = "";
      Url = FileName;
 
      return true;
    } catch (Exception ex) {
      false false;
    }
  }
}

Note: The Vimeo API can also give its data in a JSON or PHP format. This can be done easily by changing the URL’s suffix from ‘.xml’ to ‘.json’ or ‘.php’

How to get a YouTube API key

1. First, you need to login to https://code.google.com/apis/console/.
2. Then click on Services and scroll down to find the row for the YouTube Data API v3.
3. Set its status to ON and accept it’s Terms of Use.
4. Then click on API Access and in the Simple API Access area generate a new browser API key.

Note that this API key is not only for YouTube, but for many Google services such as Google Maps API, Custom Search API, etc.

Links

• YouTube API – Getting Started Guide
• Google API Console
• Vimeo API
• Vimeo Simple API

.eot   application/vnd.ms-fontobject
.ttf   application/octet-stream
.svg   image/svg+xml
.woff  application/x-woff

If you do not have access to the IIS Manager, you can add these declarations in your Web.config file, in the <system.webServer> section.

<system.webServer>
    <staticContent>
        <mimeMap fileExtension=".eot" mimeType="application/vnd.ms-fontobject" />
        <mimeMap fileExtension=".ttf" mimeType="application/octet-stream" />
        <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
        <mimeMap fileExtension=".woff" mimeType="application/x-woff" />
    </staticContent>
</system.webServer>

Update: These settings will help you if the Font Awesome fonts are not showing in IE 9 or 10.

The plugin re-sizes the image to fit to its parent element and sets margin-top or margin-left so that the image centers and crops its sides. If the image is smaller than its container, we have the option to either stretch the image so it fills its container or just center to its container. In any case the image maintains its aspect ratio.

In the case where both dimensions of the image are smaller than its parents dimensions and we don’t want to stretch the image we use a simple CSS solution, which is presented below.

.image_container {
    position:relative;
}
.image_container img {
    position:absolute;
    top:0px;
    bottom:0px;
    left:0px;
    right:0px;
    margin:auto;
}

In all other cases the script calculates the top and left margin required to center the image.

(function ($) {
    $.fn.center_img = function (options) {
        options = $.extend({}, $.fn.center_img.defaultOptions, options);
        this.each(function (idx, item) {
            var jItem = $(item);
            var jImg = jItem.find('img');
 
            if(options.set_overflow) {
                jItem.css('overflow', 'hidden');
            }
 
            var width = ((jItem.attr('data-width') == undefined) ? jItem.width() : jItem.attr('data-width'));
            var height = ((jItem.attr('data-height') == undefined) ? jItem.height() : jItem.attr('data-height'));
 
            var img_width = ((jImg.attr('data-width') == undefined) ? jImg.width() : jImg.attr('data-width'));
            var img_height = ((jImg.attr('data-height') == undefined) ? jImg.height() : jImg.attr('data-height'));
 
            if (width <= img_width && height <= img_height) {
                 if (width / height > img_width / img_height) {
                    jImg.css('max-width', width + 'px');
                    var offset = parseInt(((img_height * width / img_width) - height) / 2);
                    jImg.css('margin-top', '-' + offset + 'px');
                }
                else {
                    jImg.css('max-height', height + 'px');
                    var offset = parseInt(((img_width * height / img_height) - width) / 2);
                    jImg.css('margin-left', '-' + offset + 'px');
                }
            }
            else {
                if (options.must_fit) {
                    if (width / height > img_width / img_height) {
                        jImg.css('width', width + 'px');
                        var offset = parseInt(((img_height * width / img_width) - height) / 2);
                        jImg.css('margin-top', '-' + offset + 'px');
                    }
                    else {
                        jImg.css('height', height + 'px');
                        var offset = parseInt(((img_width * height / img_height) - width) / 2);
                        jImg.css('margin-left', '-' + offset + 'px');
                    }
                }
                else {
                    if (width > img_width && height > img_height) {
                        jItem.css('position', 'relative');
                        jImg.css('position', 'absolute').css('margin', 'auto').css('top', '0').css('bottom', '0').css('right', '0').css('left', '0');
                    }
                    else {
                        jImg.css('margin-left', parseInt((width - img_width) / 2) + 'px');
                        jImg.css('margin-top', parseInt((height - img_height) / 2) + 'px');
                    }
                }
            }
        });
        $.fn.center_img.defaultOptions = {
            must_fit: true,       // The image will re-size in order to fill its container
            set_overflow: true    // Set this to true if the image container doesn't have the css property overflow:hidden;
        }
    }
})(jQuery);

The plugin has an option that defines whether we want the image to be stretched in order to fill its container.

Note that you should call the plugin on the window.load event and not on the document.ready event, since the window.load event fires when the images of the document are loaded. Alternatively you can use the WaitForImages plugin.
On the other hand, if you know the dimensions of your image, you can assign the data-width and data-height attributes to the img tag and avoid the problematic event firing of the image loading.

In this article we will see how we can use the GridView control for this task. This approach still limits us to use a GridView, so after that we will see how we can make a Repeater (or any other control) that renders an HTML table to an excel file. The main advantage of this approach is that we don;’t present the plain data from the DataTable, but we can utilize the HTML formatting a GridView can provide and also not having to write a complex Sql Query to replace any computations we make on the GridView.

The code to export a GridView is here.

Sub GridViewToExcel(ByVal myGridView As GridView, ByVal CurrentResponse As System.Web.HttpResponse, ByVal ExcelFileName As String)
    CurrentResponse.Clear()
    CurrentResponse.Charset = ""
    CurrentResponse.ContentType = "application/vnd.ms-excel"
    CurrentResponse.AddHeader("Content-Disposition", "attachment;filename=" & ExcelFileName & ".xls")  
 
    Dim stringWrite As New System.IO.StringWriter
    Dim htmlWrite As New System.Web.UI.HtmlTextWriter(stringWrite)
    myGridView.RenderControl(htmlWrite)
    CurrentResponse.Write(stringWrite.ToString)
    CurrentResponse.End()
End Sub

With this code snippet 2 errors will occur.

One is:

You can avoid this error by adding this function to your .aspx page.

Public Overrides Sub VerifyRenderingInServerForm(control As Control)
	' Verifies that the control is rendered 
End Sub

The second is:

You can avoid this error by setting the enableEventValidation property of your page to false. This can be done by setting this globally in the Web.config file or in the @Page Directive of your .aspx file.

<%@ Page Language="VB" AutoEventWireup="true" EnableEventValidation = "false" %>

If you are don’t want to disable event validation you could put your GridView to an empty .aspx page and make the export there. Also, you could change the EnableEventValidation property via code. This can be done only in the PreInit event. There you could change its value to false.

Protected Sub Page_PreInit(sender As Object, e As EventArgs)
    If(Page.IsPostBack AndAlso Request.Form("__EVENTTARGET").Contains("ExportToExcel")) Then
        Me.Page.EnableEventValidation = False
    End If
End Sub

This is a nasty hack and also doesn’t change anything. So, we could check the control’s name that triggered the postback. Having a naming convention at least disables event validation in much less cases (still a hack though!).

The above solution doesn’t fit in cases where the data we want to export to an excel file are not rendered from a GridView control. If we have a Repeater or a combination of user controls that form an HTML table we can also create an excel file with it.
In the case of the Repeater control, we simply render our repeater to an HtmlTextWriter and flush to the response.

Sub RepeaterToExcel(ByVal myRepeater As Repeater, ByVal CurrentResponse As System.Web.HttpResponse, ByVal ExcelFileName As String)
    CurrentResponse.Clear()
    CurrentResponse.Charset = ""
    CurrentResponse.ContentType = "application/vnd.ms-excel"
    CurrentResponse.AddHeader("Content-Disposition", "attachment;filename=" & ExcelFileName & ".xls")  
 
    Dim stringWrite As New System.IO.StringWriter
    Dim htmlWrite As New System.Web.UI.HtmlTextWriter(stringWrite)
    myRepeater.RenderControl(htmlWrite)
    CurrentResponse.Write(stringWrite.ToString)
    CurrentResponse.End()
End Sub

Finally, if you have a different control you can use the function below. If you have a combination of user controls that form an HTML table you wrap them in a PlaceHolder and use the same function.

Sub ControlToExcel(ByVal myControl As Control, ByVal CurrentResponse As System.Web.HttpResponse, ByVal ExcelFileName As String)
    CurrentResponse.Clear()
    CurrentResponse.Charset = ""
    CurrentResponse.ContentType = "application/vnd.ms-excel"
    CurrentResponse.AddHeader("Content-Disposition", "attachment;filename=" & ExcelFileName & ".xls")  
 
    Dim stringWrite As New System.IO.StringWriter
    Dim htmlWrite As New System.Web.UI.HtmlTextWriter(stringWrite)
    myControl.RenderControl(htmlWrite)
    CurrentResponse.Write(stringWrite.ToString)
    CurrentResponse.End()
End Sub

In this article I will post a few simple functions that help me manipulate text that contains HTML and MS Word tags in a various ways.

All function are really small and use regular expressions.

Clear HTML Tags

This function replaces all tags with the ReplaceChar string. By default, the space character is used, because extra spaces don’t create any problem when showing the cleaned text to a web page.

Function StripHTMLTags(ByVal HTMLToStrip As String, Optional ByVal ReplaceChar As String = " ") As String
    If (HTMLToStrip <> String.Empty) Then
        Return Regex.Replace(HTMLToStrip, "", ReplaceChar)
    End If
    Return String.Empty
End Function

Clear MS Word Tags

The above function cannot clear all tags that MS Word contains. The function below does the trick. Combining both functions will give you a plain text.

Function StripWordTags(ByVal HTMLToStrip As String, Optional ByVal ReplaceChar As String = " ") As String
    StripWordTags = HTMLToStrip
    If (HTMLToStrip <> String.Empty) Then
        StripWordTags = Regex.Replace(HTMLToStrip, "\n", ReplaceChar)
        StripWordTags = Regex.Replace(StripWordTags, "\r", ReplaceChar)
        StripWordTags = Regex.Replace(StripWordTags, "<!--.+?-->", ReplaceChar)
        StripWordTags = Regex.Replace(StripWordTags, "&lt;!--.+?--&gt;", ReplaceChar)
        StripWordTags = Regex.Replace(StripWordTags, "<!--.+?-->", ReplaceChar)
        StripWordTags = Regex.Replace(StripWordTags, "]*>", ReplaceChar)
    End If
End Function
 
Function StripAllTags(ByVal HTMLToStrip As String, Optional ByVal ReplaceChar As String = " ") As String
    StripAllTags = StripWordTags(HTMLToStrip)
    StripAllTags = StripHTMLTags(StripAllTags)
End Function

String To URL

This function checks if a string is a URL and if not, it converts it to one. This comes handy to fix user input and a value is a website or domain.

Function Str2Url(ByVal Str As String) As String
    Str2Url = Str
    If (Str2Url <> "") Then
        If (Not Str2Url.StartsWith("http://") And Not Str2Url.StartsWith("https://")) Then
            Str2Url = "http://" & Str2Url
        End If
        If (Not Str2Url.EndsWith("/")) Then
            Str2Url = Str2Url & "/"
        End If
    End If
End Function

Websafe function

This function replaces from a string all invalid characters that could cause a problem in a URL, e.g. when uploading a file and its original file name contains characters that will break a URL.
Also some web servers cannot handle correctly file names with non latin characters. I have a function that converts all Greek file names to an equivalent name with Latin characters (and vice versa).

Function WebSafe(ByVal Key As String) As String
    WebSafe = Greek2GrEnglish(Key.Replace("^", "").Replace(" ", "").Replace("|", "")).ToLower()
    WebSafe = Regex.Replace(WebSafe, "[^0-9|^a-z|^A-Z|^.|^_]", "")
    WebSafe = Regex.Replace(WebSafe, "\.+", ".")
End Function
 
Function Greek2GrEnglish(ByVal GreekStr As String) As String
    Dim AllMatches() As String = "Α,A:Β,B:Γ,G:Δ,D:Ε,E:Ζ,Z:Η,I:Θ,TH:Ι,I:Κ,K:Λ,L:Μ,M:Ν,N:Ξ,KS:Ο,O:Π,P:Ρ,R:Σ,S:Τ,T:Υ,Y:Φ,F:Χ,X:Ψ,PS:Ω,W:Ά,A:Έ,E:Ή,I:Ί,I:Ό,O:Ύ,Y:Ώ,W:Ϊ,I:Ϋ,Y:ά,a:έ,e:ή,i:ί,i:ΰ,y:α,a:β,b:γ,g:δ,d:ε,e:ζ,z:η,i:θ,th:ι,i:κ,k:λ,l:μ,m:ν,n:ξ,ks:ο,o:π,p:ρ,r:ς,s:σ,s:τ,t:υ,y:φ,f:χ,x:ψ,ps:ω,w:ϊ,i:ϋ,y:ό,o:ύ,y:ώ,o:ΐ,i".Split(":")
    Dim GreekChar, EnglishChar As String
    Greek2GrEnglish = GreekStr
 
    For Each _Match As String In AllMatches
        GreekChar = _Match.Split(",")(0)
        EnglishChar = _Match.Split(",")(1)
        Greek2GrEnglish = Greek2GrEnglish.Replace(GreekChar, EnglishChar)
    Next
End Function
 
Function GrEnglish2Greek(ByVal GrEnglishStr As String) As String
    Dim AllMatches() As String = "Α,A:Β,B:Γ,G:Δ,D:Ε,E:Ζ,Z:Η,I:Θ,TH:Ι,I:Κ,K:Λ,L:Μ,M:Ν,N:Ξ,KS:Ο,O:Π,P:Ρ,R:Σ,S:Τ,T:Υ,Y:Φ,F:Χ,X:Ψ,PS:Ω,W:Ά,A:Έ,E:Ή,I:Ί,I:Ό,O:Ύ,Y:Ώ,W:Ϊ,I:Ϋ,Y:ά,a:έ,e:ή,i:ί,i:ΰ,y:α,a:β,b:γ,g:δ,d:ε,e:ζ,z:η,i:θ,th:ι,i:κ,k:λ,l:μ,m:ν,n:ξ,ks:ο,o:π,p:ρ,r:ς,s:σ,s:τ,t:υ,y:φ,f:χ,x:ψ,ps:ω,w:ϊ,i:ϋ,y:ό,o:ύ,y:ώ,o:ΐ,i".Split(":")
    Dim GreekChar, EnglishChar As String
    GrEnglish2Greek = GrEnglishStr
 
    For Each _Match As String In AllMatches
        GreekChar = _Match.Split(",")(0)
        EnglishChar = _Match.Split(",")(1)
        GrEnglish2Greek = GrEnglish2Greek.Replace(EnglishChar, GreekChar)
    Next
End Function

URLSafe function

This function is a stricter version of the WebSafe function. I am using this function when I need to upload files the RackspaceCloud’s CDN platform, Cloud Files. Also, this function uses the “-” character as the default replace character. This is also useful to create URL titles for new posts in a CMS.

Function UrlSafe(ByVal Key As String) As String
    UrlSafe = Regex.Replace(Greek2GrEnglish(Key.ToLower()), "([^_0-9a-zA-Z])", "-")
    While (UrlSafe.Contains("--"))
        UrlSafe = UrlSafe.Replace("--", "-")
    End While
    UrlSafe = UrlSafe.Trim("-")
End Function

CutText function

This function cuts a long text to a limit of characters, but also makes sure that the last word of the text will not be cut in half.

Function CutText(ByVal SomeText As String, Optional ByVal Length As Integer = 200) As String
    SomeText = Functions.StripAllTags(SomeText)
 
    If (SomeText.Length < Length + 1 Or Length = 0) Then
        Return SomeText
    Else
        Return (SomeText.Substring(0, Length + SomeText.Substring(Length).IndexOf(" ")))
    End If
End Function

GetPathFromImageTag function

This function finds an <img> HTML tag and returns the path from the src attribute

Function GetPathFromImageTag(ByVal ImageTag As String) As String
    If (Not ImageTag.Contains("src=""")) Then Return String.Empty
 
    GetPathFromImageTag = ImageTag.Substring(ImageTag.IndexOf("src=""") + 5)
    GetPathFromImageTag = GetPathFromImageTag.Substring(0, GetPathFromImageTag.IndexOf(""""))
End Function

All functions are simple and provide basic functionality. I hope that you will find them useful!

I was working in a job running the campus email system some years ago when I got a call from the chairman of the statistics department.

“We’re having a problem sending email out of the department.”

“What’s the problem?” I asked.

“We can’t send mail more than 500 miles,” the chairman explained.

I choked on my latte. “Come again?”

“We can’t send mail farther than 500 miles from here,” he repeated. “A little bit more, actually. Call it 520 miles. But no farther.”

“Um… Email really doesn’t work that way, generally,” I said, trying to keep panic out of my voice. One doesn’t display panic when speaking to a department chairman, even of a relatively impoverished department like statistics. “What makes you think you can’t send mail more than 500 miles?”

“It’s not what I *think*,” the chairman replied testily. “You see, when we first noticed this happening, a few days ago–”

“You waited a few DAYS?” I interrupted, a tremor tinging my voice. “And you couldn’t send email this whole time?”

“We could send email. Just not more than–”

“–500 miles, yes,” I finished for him, “I got that. But why didn’t you call earlier?”

“Well, we hadn’t collected enough data to be sure of what was going on until just now.” Right. This is the chairman of *statistics*. “Anyway, I asked one of the geostatisticians to look into it–”

“Geostatisticians…”

“–yes, and she’s produced a map showing the radius within which we can send email to be slightly more than 500 miles. There are a number of destinations within that radius that we can’t reach, either, or reach sporadically, but we can never email farther than this radius.”

“I see,” I said, and put my head in my hands. “When did this start? A few days ago, you said, but did anything change in your systems at that time?”

“Well, the consultant came in and patched our server and rebooted it. But I called him, and he said he didn’t touch the mail system.”

“Okay, let me take a look, and I’ll call you back,” I said, scarcely believing that I was playing along. It wasn’t April Fool’s Day. I tried to remember if someone owed me a practical joke.

I logged into their department’s server, and sent a few test mails. This was in the Research Triangle of North Carolina, and a test mail to my own account was delivered without a hitch. Ditto for one sent to Richmond, and Atlanta, and Washington. Another to Princeton (400 miles) worked.

But then I tried to send an email to Memphis (600 miles). It failed. Boston, failed. Detroit, failed. I got out my address book and started trying to narrow this down. New York (420 miles) worked, but Providence (580 miles) failed.

I was beginning to wonder if I had lost my sanity. I tried emailing a friend who lived in North Carolina, but whose ISP was in Seattle. Thankfully, it failed. If the problem had had to do with the geography of the human recipient and not his mail server, I think I would have broken down in tears.

Having established that–unbelievably–the problem as reported was true, and repeatable, I took a look at the sendmail.cf file. It looked fairly normal. In fact, it looked familiar.

I diffed it against the sendmail.cf in my home directory. It hadn’t been altered–it was a sendmail.cf I had written. And I was fairly certain I hadn’t enabled the “FAIL_MAIL_OVER_500_MILES” option. At a loss, I telnetted into the SMTP port. The server happily responded with a SunOS sendmail banner.

Wait a minute… a SunOS sendmail banner? At the time, Sun was still shipping Sendmail 5 with its operating system, even though Sendmail 8 was fairly mature. Being a good system administrator, I had standardized on Sendmail 8. And also being a good system administrator, I had written a sendmail.cf that used the nice long self-documenting option and variable names available in Sendmail 8 rather than the cryptic punctuation-mark codes that had been used in Sendmail 5.

The pieces fell into place, all at once, and I again choked on the dregs of my now-cold latte. When the consultant had “patched the server,” he had apparently upgraded the version of SunOS, and in so doing *downgraded* Sendmail. The upgrade helpfully left the sendmail.cf alone, even though it was now the wrong version.

It so happens that Sendmail 5–at least, the version that Sun shipped, which had some tweaks–could deal with the Sendmail 8 sendmail.cf, as most of the rules had at that point remained unaltered. But the new long configuration options–those it saw as junk, and skipped. And the sendmail binary had no defaults compiled in for most of these, so, finding no suitable settings in the sendmail.cf file, they were set to zero.

One of the settings that was set to zero was the timeout to connect to the remote SMTP server. Some experimentation established that on this particular machine with its typical load, a zero timeout would abort a connect call in slightly over three milliseconds.

An odd feature of our campus network at the time was that it was 100% switched. An outgoing packet wouldn’t incur a router delay until hitting the POP and reaching a router on the far side. So time to connect to a lightly-loaded remote host on a nearby network would actually largely be governed by the speed of light distance to the destination rather than by incidental router delays.

Feeling slightly giddy, I typed into my shell:

$ units
1311 units, 63 prefixes

You have: 3 millilightseconds
You want: miles
        * 558.84719
        / 0.0017893979

“500 miles, or a little bit more.”

Trey Harris,
From: http://www.ibiblio.org/harris/500milemail.html

In this article, we will discuss what ASP.NET offers and a few tips on how to use them. Finally we will leave ASP.NET and see how we can achieve the same functionality with jQuery.

1. Update Panels
2. Page Methods
3. Web Methods
4. jQuery ajax

Update Panels

Update panels are the oldest trick in the book for ASP.NET. It is the simplest way to have ajax functionality in your web application. We will not see them in depth, just mention a few basic points about them. Below is a simple example:

<asp:UpdatePanel ID="SimpleUpdatePanel" runat="server">
    <ContentTemplate>
        <asp:Button ID="AjaxButton" runat="server" Text="Button" />
        <asp:Literal ID="MessageLiteral" runat="server"></asp:Literal>
    </ContentTemplate>
</asp:UpdatePanel>

Protected Sub AjaxButton_Click(sender As Object, e As EventArgs) Handles AjaxButton.Click
    MessageLiteral.Text = "Ajax update occured"
End Sub

In code behind, you have access to the entire form. That is possible because when an update panel refreshes, the whole form is been posted to the web server. But only the markup of the update panel can change. So, if we try to change something that it is not inside our update panel the change will not happen.

It is that simple to have ajax functionality in your web application. We can also assign some event handlers so when an update panel refreshes we can execute some JavaScript code.

var prm = Sys.WebForms.PageRequestManager.getInstance();
 
prm.add_beginRequest(BeginRequestHandler);
prm.add_endRequest(EndRequestHandler);
 
function BeginRequestHandler(sender, args) {
    //code that runs when an UpdatePanel starts refreshing
}
 
function EndRequestHandler(sender, args) {
    //code that runs when an UpdatePanel has refreshed.
}

With that level of abstraction, it is pretty clear than it is not a very optimal approach. If an update panel encloses a big part of the web form, it will be much slower. Even having a small update panel, the whole form is posted to the server, including the ViewState.

Generally it is not a good practice to have nested update panels in a big depth (up to 2 is generally ok). Finally, different update panels cannot refresh simultaneously. You can read about it (and a workaround for it) here.

Page Methods

With update panels we can update html sections of our web page. There is no direct way to get a value (e.g. a string or an integer) via ajax. For that, we can use page methods.
Page methods are static methods declared in code behind and are exposed via JavaScript int the client. Page methods are much more lightweight since they don’t post nothing from the form, except what necessary parameters each method has.

In the following example you see a sample page method. You have to enable page methods in the ScriptManager. When calling the method in JavaScript you can set two function as attributes that will behave as success and error handlers of the ajax call.
ASP.NET part

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true">
</asp:ScriptManager>
<div>
    <asp:Button ID="PageMethodButton" runat="server" Text="Call Page Method" OnClientClick="javascript:call_page_method(); return false;" />
</div>
</form>

JavaScript part

function success(data) {
    alert(data);
}
 
function error() {
    ...
}
 
function call_page_method() {
    PageMethods.HelloWorld(false, success, error);
}

Code Behind part (vb.net)

Imports System.Web.Services
 
Public Class _default
    Inherits System.Web.UI.Page
    ...
 
    <WebMethod()> _
    Public Shared Function HelloWorld(ByVal LowerCase As Boolean) As String
        If (LowerCase) Then Return ("Hello World").ToLower
        Return "Hello World"
    End Function
End Class

Page methods are lightweight. One disadvantage is that we can only use them in .aspx pages. We cannot declare a page method in a user control. Also, the JavaScript declaration of the method is embedded directly into the HTML. So, having many page methods will lead to bigger HTML files. Also, there is no way to declare them in a single place so that our entire web application can make use of them.

Web Methods

Page methods can be very useful and practical. In the scenarios where we would like to have such methods declared globally we can use Web methods. We can declare our methods in a .asmx file. When we create the new .asmx file we need to uncomment one line of code, as the comments on the top of the page suggest.

Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.ComponentModel
 
' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
<System.Web.Script.Services.ScriptService()> _
<System.Web.Services.WebService(Namespace:="http://tempuri.org/")> _
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class myMethods
    Inherits System.Web.Services.WebService
 
    <WebMethod()> _
    Public Shared Function HelloWorld(ByVal LowerCase As Boolean) As String
        If (LowerCase) Then Return ("Hello World").ToLower
        Return "Hello World"
    End Function
End Class

In order to use the declared web methods, we need to register the .asmx service to our script manager. This can be in the asp.net markup or in the code behind.

<asp:ScriptManager ID="ScriptManager1" runat="server">
    <Services>
        <asp:ServiceReference Path="~/myMethods.asmx" />
    </Services>
</asp:ScriptManager>

Finally, to use the web method in our JavaScript code we need to write the full namespace. For example:

function call_web_method() {
    DemoWebApplication.myMethods.HelloWorld(true, success, error);
}

jQuery ajax

With jQuery you can also make asynchronous calls to the server and gives you more flexibility while developing your application. You can see and example of jQuery.ajax in the following snippet.

jQuery.ajax({ 
    url: '/ajax_handlers/example-handler.ashx',
    context: document.body,
    cache: false,
    type: 'GET';
    contentType: 'application/json',
    success: function (data) {
        var server_response = data; //This is the data the server returned
    }, 
    error: handle_ajax_error
});
 
// Here is a error handler stating some useful values regarding the error occured.
function handle_ajax_error(xhr, ajaxOptions, thrownError) { 
    alert('error: ' + xhr.responseText + '__' + thrownError + '__' + xhr.statusText); 
}

There are a couple of things to consider. One is that you may get errors if the response’s data type is not what jQuery expects. Also, you should use the ‘cache’ property and set it to false when you expect fresh data from the server. It’s default value is true.

For more information and options you can visit the documentation page for jQuery.ajax.

Comparing approaches

The main question that could rise here is what approach should someone use. In every case there are some advantages and disadvantages. With ASP.NET tools the development is a bit easier and faster. With jQuery there are some issues that the developer will need to address (contentType issues, encoding issues, etc) while the ASP.NET tools handle these things internally.
One disadvantage of the ASP.NET approach is that in any case the page must have one big form (runat=”server”). In a busy website this element might be better to be omitted and so jQuery is the (only) way to go.

In any case, the developer should know how to use jQuery in any case, since it is also used in ASP.NET MVC and most important it is not platform specific.

Related articles

We have seen how we can introduce ajax in our web application. The above article is an introduction for the above techniques. Below are a few articles related to the topic, that provide more specific information for them. The blog of Dave Ward has many useful and interesting articles regarding ASP.NET Ajax and jQuery.

• Why ASP.NET AJAX UpdatePanels are dangerous
• Simultaneous async requests with multiple Update Panels
• Using jQuery to directly call ASP.NET AJAX page methods
• Easily refresh an UpdatePanel, using JavaScript