Using WCF REST Starter Kit to Access Constant Contact API

james — Fri, 01 May 2009 19:30:37 +0000

Problem: Allow customers to sign up for email newsletters and synchronize those accounts with Constant Contact.

Constant Contact is a company that provides Email Marketing services. You can use their editor to create nice looking emails and then configure a list of contacts. Constant Contact handles all the email sending, bounces, and unsubscribe activities. They also provide excellent reporting features to track how many people actually view your emails or click on the contained links.

The nice folks at Constant Contact provide a set of web services for accessing account data. These interfaces are implemented as REST services utilizing the Atom Publication Protocol (AtomPub) and Atom Syndication Format. At first it might seem odd to be accessing data objects via a blogging protocol but it actually works quite naturally. So well that Google’s GData and Microsoft’s ADO.NET Data Services also support this technique.

Writing all the HTTP, Auth, and XML parsing code can be a real drag. Luckily Microsoft is releasing a WCF REST Starter Kit. From the CodePlex summary:

The WCF REST Starter Kit is a set of .Net Framework classes and Visual Studio features and templates that enable users to create and access REST-style Windows Communication Foundation (WCF) services. These services are based on the WCF web programming model available in .Net 3.5 SP1. The starter kit also contains the full source code for all features, detailed code samples, and unit tests.

This starter kit makes accessing the Constant Contact API quite simple. Call GetEntry or GetFeed with a URI and get back a SyndicationItem or SyndicationFeed (collection of items). Similar methods exist for adding and updating data (AddEntry and UpdateEntry).

The following is one method from my ContactListProvider class:

public ContactList GetContactList(string id)
{
AtomPubClient client = new AtomPubClient();
client.TransportSettings.Credentials = GetLoginCredentials();

// Place in a try block to ensure that any errors are caught
try
{
SyndicationItem item = client.GetEntry(new Uri(id));

ContactList list = new ContactList(item.Content as XmlSyndicationContent);

return list;
}
catch (WebException ex)
{
_log.Error("WebException: " + ex.Status + " " + ex.Message, ex);
return null;
}
catch (Exception ex)
{
// Get the exception type
_log.Error("Exception: " + ex.Message, ex);
return null;
}
}

Contact me via comments if you want a copy of all the providers.

How to convert UPC-A to zero-compressed UPC-E

james — Thu, 30 Apr 2009 22:59:32 +0000

Universal Product Codes (UPCs) should be a very straight-forward topic. You give a product a number and that is the end of the story. Unfortunately it turns out to be a bit more complicated than that.

There is a great (well I guess that’s subjective) page on Wikipedia that does an excellent job explaining all the variations: Universal Product Codes. There are 14, 13, 12, 11, 10, 8, and 6 digit types of UPCs. There is also an interesting algorithm to convert from a fairly standard 12-digit UPC-A code into a zero-compressed UPC-E. This is a most uninteresting fact. Until the day comes when you actually have to convert some of these codes.

Here is some C# code to:

Convert UPC-A codes to UPC-E
Convert UPC-E codes to UPC-A
Calculate check digits

If google brought you here because you need these conversions then bask is it’s yucky goodness! If not, then just move right along (basically it’s a cup with dirt in it).

public string ConvertUPCAToUPCE(string UPCa)
{
string UPCe = "";

//Must be 12 digits
if (UPCa.Length != 12)
{
return "";
}

string mfg = UPCa.Substring( 1, 5);
string prod = UPCa.Substring(6, 5);

if ((mfg.Substring(2) == "000") || (mfg.Substring(2) == "100") ||(mfg.Substring(2) == "200") )
{
// 0 XXNNN0 0XX000-00NNN + check
// 1 XXNNN1 0XX100-00NNN + check
// 2 XXNNN2 0XX200-00NNN + check
UPCe = mfg.Substring(0, 2) + prod.Substring(2, 3) + mfg.Substring(2, 1);
}
else if (mfg.Substring(3,2) == "00")
{
// 3 XXXNN3 0XXX00-000NN + check
UPCe = mfg.Substring(0,3) + prod.Substring(3,2) + "3";
}
else if (mfg.Substring(4, 1) == "0")
{
// 4 XXXXN4 0XXXX0-0000N + check
UPCe = mfg.Substring(0, 4) + prod.Substring(4,1) + "4";
}
else
{
// 5 XXXXX5 0XXXXX-00005 + check
// 6 XXXXX6 0XXXXX-00006 + check
// 7 XXXXX7 0XXXXX-00007 + check
// 8 XXXXX8 0XXXXX-00008 + check
// 9 XXXXX9 0XXXXX-00009 + check
UPCe = mfg + prod.Substring(4);
}

return UPCe;
}

public string ConvertUPCEToUPCA(string UPCe)
{
//Must be 12 digits
if (UPCe.Length != 6)
{
return "";
}

string mfg = "";
string prod = "";

switch (UPCe.Substring(5, 1))
{
case "0":
mfg = "0" + UPCe.Substring(0, 2) + "000";
prod = "00" + UPCe.Substring(2, 3);
break;

case "1":
mfg = "0" + UPCe.Substring(0, 2) + "100";
prod = "00" + UPCe.Substring(2, 3);
break;

case "2":
mfg = "0" + UPCe.Substring(0, 2) + "200";
prod = "00" + UPCe.Substring(2, 3);
break;

case "3":
mfg = "0" + UPCe.Substring(0, 3) + "00";
prod = "000" + UPCe.Substring(3, 2);
break;

case "4":
mfg = "0" + UPCe.Substring(0, 4) + "0";
prod = "0000" + UPCe.Substring(4, 1);
break;

default:
mfg = "0" + UPCe.Substring(0, 5);
prod = "0000" + UPCe.Substring(5, 1);
break;
}

return mfg + prod + CalculateCheckDigit(mfg + prod);
}

//In the UPC-A system, the check digit is calculated as follows:
//
// 1. Add the digits in the odd-numbered positions (first, third, fifth, etc.) together and multiply by three.
// 2. Add the digits in the even-numbered positions (second, fourth, sixth, etc.) to the result.
// 3. Find the result modulo 10 (i.e. the remainder when the result is divided by 10).
// 4. If the result is not zero, subtract the result from ten.
//
private string CalculateCheckDigit(string upc)
{
int check = 0;
char[] chars = upc.ToCharArray();

// process string from right to left
Array.Reverse(chars);

for (int i =0;i<chars.Length;i++)
{
if ((i % 2)!= 0)
{
// even
check += int.Parse(chars[i].ToString());
}
else
{
// odd
check += (3 * int.Parse(chars[i].ToString()));
}
}

check = check % 10;

if (check != 0)
{
check = 10 - check;
}

return check.ToString();
}

Update: CheckDigit right to left processing.

freemind blogs » c#

Using WCF REST Starter Kit to Access Constant Contact API

How to convert UPC-A to zero-compressed UPC-E