A good application is ubiquitous, it is everywhere you need it and never in your way. That is probably why applications like Twitter and Facebook have been so successful. So how do you add more of that ubiqutous goodness into your applications? SMS of course! Text messaging is a powerful tool for many people. I text more than I talk, and I think that is becoming the status quo.  That in mind, I have been looking for a good SMS gateway provider so that I can give texting capabilities to my clients. I still haven’t stumbled on the best solution, but there is one worth talking about: Zeep Mobile.

Zeep Mobile is a Free SMS Gateway for use without any limitations, but there is a catch. The catch is with each message you send  your users, a small text based ad will be placed in your at the end of the message. If you don’t want ads, you can pay for an ad free service. So I signed up for the beta and decided to figure out how well it works.

Step 1 – Sign Up For Beta

Go to the Zeep Mobile site and sign up for the Beta, you should get an invitation almost instantly. This is a Beta, so I didn’t expect everything to work or have a super refined service.

Step 2 – Understanding the Flow

You can’t start sending messages to anyone you want. This is a subscription based system. So you have to follow these steps to get started.

1. Create  an application key within Zeep Mobile
2. Copy a provided HTML Snippet onto your site
3. Sign up through the provided widget with a valid number or test number (provided by Zeep Mobile).
4. Confirm on that number that you want text messages from said application.
5. The Application is now ready to send that number text messages.

Step 3 – Following Their API

Zeep Mobile is a REST based API, which means all your interactions will be facilitated through the HTTP protocol; mainly posting your data to them. Also, their authorization scheme is based on a secret key and hashing your content along with the current date of the request. See the diagram below.

In addition to sending text messages, Zeep Mobile can make calls to an endpoint of yours and pass you data. This is so your application can store and maintain the latest users. I’ll show you how to send text messages to Zeep, but I won’t show the callback because that is trivial to implement once I show you how to call Zeep Mobile.

Creating Your Zeep Authorization Token

Zeep Mobile requires you have your authorization token in the header. It follows the following format.

Zeep [API Key]:[HMAC+SHA1 Encoded Canonical]

Being a nice guy, the following code to do that is directly below. One note, before you pass the message into the method below, make sure to Url Encode the string. This can be done by using the HttpUtility class. I’ve also provided extension methods to do this.

        public string GetZeepAuthorization(string message, DateTime date)
        {
            // product HTTP Date
            var httpDate = date.ToString("r");
            string canonicalString = ApiKey + httpDate + message;

            // Compute the Base64 HMACSHA1 value
            HMACSHA1 hmacsha1 = new HMACSHA1(SecretAccessKey.ToByteArray());

            // Compute the hash of the input file.
            byte[] hashValue = hmacsha1.ComputeHash(canonicalString.ToByteArray());

            string b64Mac = hashValue.ToBase64String();
            return string.Format("Zeep {0}:{1}", ApiKey, b64Mac);
        }

 public static class Extensions
    {
        public static byte[] ToByteArray(this string input)
        {
            UTF8Encoding encoding = new UTF8Encoding();
            return encoding.GetBytes(input);
        }

        public static string ToBase64String(this byte[] input)
        {
            return Convert.ToBase64String(input);
        }

        public static string ToUrlEncoded(this string input)
        {
            return HttpUtility.UrlEncode(input, Encoding.UTF8);
        }
    }

Posting Your Text Message

You have two options here: Send a message to a particular user or send the message to everyone. The code below shows you how to send to everyone, but this code is easily adapted to send to a single user. The quirk below is that you have to set the date on your request or Zeep will complain. Zeep uses the date to calculate the hash on their side, if the date is missing then you can’t get your request through. Read the documentation on Zeep Mobile for more detailed information.

  public string SendZeepMessage(string message, string authorization, DateTime date)
        {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(BlastMessage);

            request.Date = date;
            request.Method = "POST";
            request.Headers.Add("Authorization", authorization);
            request.ContentType = "application/x-www-form-urlencoded";

            // send the Post
            var messageBytes = message.ToByteArray();
            request.ContentLength = messageBytes.Length;

            using (var os = request.GetRequestStream())
                os.Write(messageBytes, 0, messageBytes.Length);

            try
            { // get the response
                WebResponse webResponse = request.GetResponse();

                using (var stream = new StreamReader(webResponse.GetResponseStream()))
                    return stream.ReadToEnd().Trim();
            }
            catch (WebException wex)
            {
                // This exception will be raised if the server didn't return 200 - OK
                // Try to retrieve more information about the network error
                using (HttpWebResponse errorResponse = (HttpWebResponse)wex.Response)
                {
                    // get descriptive message
                    using (StreamReader sr = new StreamReader(errorResponse.GetResponseStream()))
                        return sr.ReadToEnd().Trim();
                }
            }
        }

That’s all the code you need to start sending text messages to subscribers. Now all you need to do is write a way to handle callbacks, possibly through an HttpHandler, ASP.NET Web Form Page, or ASP.NET MVC.

Get Your Message (err… Sorta)

At the time I wrote this code, everything was working fine on Zeep Mobile but something must have broken on their side. How can I be certain it is on their side and not my code? Well messages are getting through. This means that hash on my messages are being calculated and are successful on Zeep Mobile’s side, but the messages coming through are blank. Hopefully this is just a small hiccup in the Beta. Below you will see the test phone that Zeep Mobile Provides.

Step 4 – Thoughts About Zeep Mobile

It is definitely a winning idea, but it is still in beta. As you saw above things are still being worked out with the API and the API lacks a lot of the calls needed to really make it something great. Essentially the API was designed to facilitate text messaging, but has left out  administration features that would allow you to manage your subscribers. The good side to that lack of functionality is that you could code it yourself due to the nature of the callback service Zeep Mobile provides. Essentially, Zeep Mobile is saying that they want to facilitate communication between you and your subscribers, but doing anything more is up to you.

Zeep Mobile is worth checking out and trying, but as of right now I would look for a stronger SMS Gateway Provider for any serious application. The downside to using other SMS Gateway providers is that they are expensive. If anybody knows any good ones please let me know, because I am always interested.