This guide gives you details about how to use C# application with
HttpListener to receive SMS messages and to generate a response SMS messages. This
solution can be used with either a GSM modem or with IP SMS.
If you use modem, then it is an in-house solution, which means you do not need
to sign up for an SMS service provided by SMS service providers over the Internet.
You only need to purchase a GSM Modem with a datacable.
If you wish to use an IP SMS, you need to make an agreement with an SMS service
provider, and ask for IP address, port number, a username and a password.
Introduction
In order to receive SMS messages with a built in webserver in a C#
application, you need an SMS Gateway, like Ozeki NG - SMS Gateway, you need
a GSM Modem and a data cable. First of all, you have to attach your GSM Modem
with the data cable to the serial (RS232) port of your PC. After that, you have
to configure the SMS gateway, so it can talk to the modem and forward the
incoming messages to the C# application.
Figure 1 illustrates the architecture of your setup. On this figure, you can see
the process of message sending, which is the following: the Mobile user sends
an SMS message to the GSM Modem attached to the computer.
Ozeki NG - SMS gateway collects this message from
the modem and forwards it to the C# application with an HTTP request. The C#
application generates an HTTP response to the request. This HTTP response
contains the content of the response SMS message. This response SMS message will
be forwarded to the Mobile user with the help of the the GSM Modem.
Figure 1. - Overview of SMS Gateway to ASP.NET architecture
Configure your SMS Gateway
First of all, you need to install and configure the SMS gateway in order to get
this setup running. Ozeki NG - SMS Gateway can be downloaded from
www.ozekisms.com. Use this gateway because it is reliable, user-friendly,
easy to configure and it is based on .NET, which means that it can be integrated
well to your architecture. To make this SMS gateway work, you need to configure
the GSM modem attached to your PC. This can be done easily by adding a GSM Modem
service provider connection. Here are the steps:
Step 1.) Open http://127.0.0.1:8080 in Internet Explorer, login with admin/abc123
Step 2.) In the "Service provider connections" menu click on "Add service
provider connection", then select "GSM Modem Connection" and click "Install"
Step 3.) Select the com port (usually COM1) on the GSM modem configuration form and
click on autodetect to configure the modem
If you are finished with this, you need to configure an HTTP client user, that will
forward the incoming
messages to your C sharp application (Figure 2). This is an automated user, which
is able to forward the messages to your application and process the HTTP responses.
Figure 2 - Installing a Http Client user
Step 4.) To install the HTTP Client user, select "Users and applications"
menu and click on "Add user", here, select "HTTPClient user" and click on "install".
Step 5.) For username provide "httpclient1"
Step 6.) For Target URL enter:
http://127.0.0.1:8080/?sender=$originator&receiver=$recipient&msgdata=$messagedata&
recvtime=$receivedtime&msgid=$messageid
Figure 3 - HTTP Target URL setting
Step 7.) It is suggested to turn on detailed logging, which can be done by enabling
the "Log low level communication" checkbox.
After these configuration steps, your SMS Gateway setup will look like this:
Figure 4 - SMS Gateway setup
Figure 4 - SMS Gateway setup
Build your C# application
Once you have the SMS Gateway configured, you can build your C#
application. This application's built in webserver is HttpListener.
HttpListener is a very efficient webserver available on Windows XP SP2 and
Windows 2003 or later windows version such as Windows Vista. The HttpListener
class is part of the System.Net package and it comes
with .NET Framework 2.0.
If you take a look at the source code (Figure 5) you will see that as a first step
of getting this solution running, you need to register the "http://127.0.0.1:8080/"
address as your URL prefix. Please note,
that this URL is configured into the SMS Gateway HTTP Client user.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Threading;
namespace httplistener_console
{
class Program
{
static void Main(string[] args)
{
try
{
HttpListener listener = new HttpListener();
//The listeningURL will hold the listening URL
string listeningURL = "http://+:8080/";
listener.Prefixes.Add(listeningURL);
listener.Start();
Console.WriteLine("Ozeki HTTP server - Listening started at {0}", listeningURL);
while (listener.IsListening)
{
HttpListenerContext context = listener.GetContext();
try
{
Thread t = new Thread(() =>
{
//Querying the sender address
string sender = context.Request.QueryString["sender"];
//"message" variable holds the response message
string message = "Thank you for your message";
string response = "{SMS:TEXT}{}{+1234657}{" + sender + "}{" + message + "}";
byte[] Buffer = System.Text.Encoding.UTF8.GetBytes(response);
context.Response.ContentType = "text/html; charset=utf-8";
context.Response.OutputStream.Write(Buffer, 0, Buffer.Length);
context.Response.Close();
//writing the sent message into the console
Console.WriteLine("Message sent to {0}. Data: {1}", sender, message);
Console.ReadLine();
});
t.Start();
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
}
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
}
}
}
Figure 5 - Source code for receiving SMS messages through HTTP
The request subrouting is called asynchronously when an incoming SMS arrives.
This sub is very simple, it calls the process request function to serve the
requests.
The process request subroutine has two main parts: the first part reads the message
from the HTTP requests and displays a MessageBox. The second part generates a
response
by writing to the Outputstream. The output will be encoded in UTF8 to support
international characters. This is achieved by using UTF 8 encoding in the
System.Text.Encoding.UTF8.GetBytes statement.
Summary
This guide was a simple example of how to use C# application with a built in webserver
to receive incoming messages and send responses. The guide showed how to configure
an HTTP - SMS Gateway and demonstrated the capabilities of HttpListener class. This
example application can be developed to several real-life solutions.
