Node by example: 7. net module
Published on April 29, 2010
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7. net module
The complete source code can be downloaded here: http://github.com/Hendrik/node-by-example
With the release of node v0.1.91, the previously existing "tcp" module has been renamed to "net". It provides 2 main objects, net.Server, which is used to create a TCP or UNIX server, and net.Stream, which is an abstraction of a TCP or UNIX socket.
Use
require('dns')
to access the features of this module.
The following is a tcp server and client example that listens on port 8000.
See 07_net/net_server.js
// based on http://nodejs.org/api.html#net-server-183
var sys = require("sys"),
net = require("net");
var server = net.createServer(function(stream) {
stream.setEncoding("utf8");
stream.addListener("connect", function() {
sys.puts("Client connected");
stream.write("hello\r\n");
});
stream.addListener("data", function(data) {
sys.puts("Received from client: " + data);
stream.write(data);
});
stream.addListener("end", function() {
sys.puts("Client disconnected");
stream.write("goodbye\r\n");
stream.end();
});
});
server.listen(8000, "localhost");
// stop the server after 10 secs
setTimeout(function() {
server.close();
}, 10000);
Create the server and make it listen to port 8000 on "localhost":
var server = net.createServer(function(stream) { ... });
server.listen(8000, "localhost");
Set the encoding of the stream:
stream.setEncoding("utf8");
The net.Stream object instances are an EventEmitter with the following events: 'connect': emmited when a stream connection is successfully established
'data': emmited when data is received, comes with a 'data' argument, which will be a Buffer or a String
'end': emmited when the other end of the stream sends a FIN packet
The following code will output "Client connected" to the console and send "hello\r\n" to the client upon a successful connection:
stream.addListener("connect", function() {
sys.puts("Client connected");
stream.write("hello\r\n");
});
Whenever the client sends data, the script will output "Received from client: [data]" to the console and send the sent data back to the client:
stream.addListener("data", function(data) {
sys.puts("Received from client: " + data);
stream.write(data);
});
When the client ends the connection "Client disconnected" will be sent to the console and a "goodbye\r\n" will be sent to the client.
stream.end() then sends a FIN packet to the client:
stream.addListener("end", function() {
sys.puts("Client disconnected");
stream.write("goodbye\r\n");
stream.end();
});
Additionally the server will be closed automatically after 10 seconds:
// stop the server after 10 secs
setTimeout(function() {
server.close();
}, 10000);
In order to run the full example please first start the server via
node net_server.js
and then start the client via
node net_client.js
Then monitor the output in both consoles, which will be similar to:
net_server.js: Client connected net_client.js: Client connected. net_client.js: Response from server: hello net_client.js: Sent to server: close net_server.js: Received from client: close net_client.js: Response from server: close net_client.js: Response from server: goodbye net_server.js: Client disconnected net_client.js: Disconnected from server
Let's see what the client does:
See 07_net/net_client.js
var sys = require("sys"),
net = require("net");
var client = net.createConnection(8000);
client.setEncoding("UTF8");
client.addListener("connect", function() {
sys.puts("Client connected.");
// close connection after 2sec
setTimeout(function() {
sys.puts("Sent to server: close");
client.write("close", "UTF8");
}, 2000);
});
client.addListener("data", function(data) {
sys.puts("Response from server: " + data);
if (data == "close") client.end();
});
client.addListener("close", function(data) {
sys.puts("Disconnected from server");
});
Create the client and make it connect to port 8000. Set the encoding type to utf8.
var client = net.createConnection(8000);
client.setEncoding("UTF8");
net.createConnection() uses "localhost" by default, but you can change it to a different host, e.g.: 127.0.0.1, using:
net.createConnection(8000, "127.0.0.1");
As mentioned in the server example, the stream object comes with the "connect", "data" and "close" event emitters.
In this case the client will send "Client connected." to the console after a successful connection has been established and then start a timer to close the connection automatically after 2 seconds:
client.addListener("connect", function() {
sys.puts("Client connected.");
// close connection after 2sec
setTimeout(function() {
sys.puts("Sent to server: close");
client.write("close", "UTF8");
}, 2000);
});
When the client receives data from the server it will send "Response from server: [data]" to the console and in case the sent data is "close", it will also (half) close the stream by sending a FIN packet to the server:
client.addListener("data", function(data) {
sys.puts("Response from server: " + data);
if (data == "close") client.end();
});
Once the connection has been closed, the client will output "Disconnected from server" to the console:
client.addListener("close", function(data) {
sys.puts("Disconnected from server");
});
This is just a basic example of a tcp server & client app, please refer to the official documentation for further details: http://nodejs.org/api.html#net-server-183