How to Use Edge.js to Empower WebSocket Solutions in JavaScript
A few days ago, I read the article - Run .NET and Node.js code in-process with Edge.js, which inspired me to try a new way of WebSocket solutions in JavaScript. It is known that Node.js makes applications, which written in JavaScript, run on server-side. Let’s see how we can quickly implement image transmission between servers and clients in a few lines of code.
Loading Image Files in JavaScript and .NET
Generally, we can load image files in JavaScript like this:
var fs = require('fs');
fs.readFile('Capture.jpg', function(err, data) {
console.log(data.length); // image data
});
The Edge.js connects Node.js and .NET in process. We can script C# from a Node.js process. To install edge package:
npm install edge
Let’s create a C# file nativeImageLoader.cs, and write a piece of code:
#r "System.Drawing.dll"
using System.Threading.Tasks;
using System.Drawing;
public class Startup
{
public async Task<object> Invoke(object input)
{
byte[] imageBuffer;
Image image = Image.FromFile("Capture.jpg");
using (System.IO.MemoryStream stream = new System.IO.MemoryStream())
{
image.Save(stream, System.Drawing.Imaging.ImageFormat.Jpeg);
imageBuffer = stream.GetBuffer();
}
return imageBuffer;
}
}
By default, edge only references mscorlib.dll and System.dll. The #r “System.Drawing.dll” is used for loading additional assemblies.
Now we can get the JavaScript proxy:
var nativeImageLoader = edge.func(require('path').join(\_\_dirname, 'nativeImageLoader.cs'));
nativeImageLoader('load', function(error, result) {
if (error) throw error;
// result is the loaded image
});
Create a WebSocket Server in JavaScript
To install WebSocket package:
npm install ws
Create and launch a WebSocket server:
var WebSocketServer = require('ws').Server,
wss = new WebSocketServer({
port: 8080
});
wss.on('connection', function(ws) {
ws.on('message', function(message) {
console.log('Received: %s', message);
nativeImageLoader('load', function(error, result) {
if (error) throw error;
ws.send(result); // send the captured image
});
});
});
Run the server:
node server.js
In client.js, set the binary type of WebSocket:
var ws = new WebSocket("ws://127.0.0.1:8080/");
ws.binaryType = "arraybuffer";
ws.onopen = function() {
alert("Opened");
ws.send("I'm Dynamsoft");
};
ws.onmessage = function (evt) {
var bytes = new Uint8Array(evt.data);
var data = "";
var len = bytes.byteLength;
for (var i = 0; i < len; ++i) {
data += String.fromCharCode(bytes[i]);
}
var img = document.getElementById("image");
img.src = "data:image/png;base64,"+window.btoa(data);
};
ws.onclose = function() {
alert("Closed");
};
ws.onerror = function(err) {
alert("Error: " + err);
};
Open client.htm to receive the loaded image.
