Sharing Links Physically

Why should we only share things we like on Facebook, Twitter or by email?

I’ve imagined a fun application with one of these small thermal printers. Although these printers are really Arduino friendly I coded a .Net class to use them directly with a computer. Then, I made a simple Safari extension which allows to print the URL of the current page… with a QR Code, of course!

The width of a paper roll is perfect for this purpose, and giving a piece of paper to share a link might be quite fun.

This extension sends a command to a small server app which is a background service connected to the printer. It’s not perfect, I’ve made it rather quickly, but it works fine.

I used the MessagingToolkit’s QR Code open source library. Ok, let’s have a look at it.

First, go to a new website everyone’s talking about on the Web.

Let’s say you want to share this crazy video with a friend. It’s time to click on the magic button:

And now here is what’s happening in the real world:

Technically, I used my .Net class in a server app. I made my own server standalone executable, coded in C#/Mono. You can find the source code on GitHub.

The core of the Safari extension is some simple javascript (code from openjs.com):

function printqrcode(url)
{
	var postURL = "http://localhost:5555/printqrcode"; //That's my server app.
	var params = "url="+escape(url);
	var http = new XMLHttpRequest();

	http.open("POST", postURL, true);
	//Send the proper header information along with the request
	http.setRequestHeader("Content-type","application/x-www-form-urlencoded");
	http.setRequestHeader("Content-length", params.length);
	http.setRequestHeader("Connection", "close");

	http.onreadystatechange = function() {//Call a function when the
                                              // state changes.
		if(http.readyState == 4 && http.status == 200) {
			alert("QR Code printed.");
		}
	}
	http.send(params);
}

As you can see my server application is a restful service which is waiting for the “printqrcode” command. Here is a piece of the C# code :

if (_postParameters.Get("url") != null) {
	url = _postParameters.GetValues("url")[0];
	if (!MainClass.printerHandler.isPrinting && !(url == null || url == "")) {
        //Resets the printer
	MainClass.printerHandler.Reset();
	MainClass.printerHandler.isPrinting = true;

     	//Prints QR Code, in one line  
	printer.PrintImage(new QRHandler(url).GetImage());

	System.Threading.Thread.Sleep(1000);

	//Formats short URL
	if (url.StartsWith("http://",true,CultureInfo.CurrentCulture))
	{
		url = url.Substring(7); //removes http://
	}
	if (url.StartsWith("www.",true,CultureInfo.CurrentCulture))
	{
		url = url.Substring(4); //removes www.
	}
	url = url.TrimEnd('/'); //removes the trailing slash
	if (url.Length > 32) {
		url = url.Substring(0,29) + "..."; //shortens to 32 chars
	}
	printer.SetLineSpacing(0);
	printer.LineFeed();
	printer.SetAlignCenter();
        //Let's print the URL
	if (url.Length > 16) {
		printer.WriteLine(url); //prints
	} else {
                //Double width if less than 16 chars long
		printer.WriteLine(url,ThermalPrinter.PrintingStyle.DoubleWidth);
	}
	printer.LineFeed();
	printer.LineFeed();
	printer.LineFeed();
	MainClass.printerHandler.isPrinting = false;
}
}

And it works!

There are things I can improve, like a configuration file or why not printing images directly from the browser. To be continued…

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