The net
module provides you with an asynchronous network wrapper. It contains functions for creating both servers and clients (called streams). You can include this module with require('net');
.
This class is used to create a TCP or local server.
net.Server
is an EventEmitter
with the following events:
Emitted when the server closes. Note that if connections exist, this event is not emitted until all connections are ended.
Emitted when a new connection is made. socket
is an instance of net.Socket
.
Emitted when an error occurs. Unlike net.Socket
, the 'close'
event will not be emitted directly following this event unless server.close()
is manually called. See the example in discussion of server.listen()
.
Emitted when the server has been bound after calling server.listen
.
Returns the bound address, the address family name, and port of the server as reported by the operating system if listening on an IP socket. Useful to find which port was assigned when getting an OS-assigned address. Returns an object with port
, family
, and address
properties: { port: 12346, family: 'IPv4', address: '127.0.0.1' }
For a server listening on a pipe or UNIX domain socket, the name is returned as a string.
Example:
const server = net.createServer((socket) => { socket.end('goodbye\n'); }).on('error', (err) => { // handle errors here throw err; }); // grab a random port. server.listen(() => { console.log('opened server on', server.address()); });
Don't call server.address()
until the 'listening'
event has been emitted.
Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a 'close'
event. The optional callback
will be called once the 'close'
event occurs. Unlike that event, it will be called with an Error as its only argument if the server was not open when it was closed.
Returns server
.
server.getConnections()
instead.The number of concurrent connections on the server.
This becomes null
when sending a socket to a child with child_process.fork()
. To poll forks and get current number of active connections use asynchronous server.getConnections
instead.
Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.
Callback should take two arguments err
and count
.
handle
<Object>
backlog
<number>
callback
<Function>
The handle
object can be set to either a server or socket (anything with an underlying _handle
member), or a {fd: <n>}
object.
This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.
Listening on a file descriptor is not supported on Windows.
This function is asynchronous. When the server has been bound, 'listening'
event will be emitted. The last parameter callback
will be added as a listener for the 'listening'
event.
The parameter backlog
behaves the same as in server.listen([port][, hostname][, backlog][, callback])
.
options
<Object> - Required. Supports the following properties: callback
<Function> - Optional.The port
, host
, and backlog
properties of options
, as well as the optional callback function, behave as they do on a call to server.listen([port][, hostname][, backlog][, callback])
. Alternatively, the path
option can be used to specify a UNIX socket.
If exclusive
is false
(default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When exclusive
is true
, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below.
server.listen({ host: 'localhost', port: 80, exclusive: true });
Note: The server.listen()
method may be called multiple times. Each subsequent call will re-open the server using the provided options.
path
<string>
backlog
<number>
callback
<Function>
Start a local socket server listening for connections on the given path
.
This function is asynchronous. When the server has been bound, 'listening'
event will be emitted. The last parameter callback
will be added as a listener for the 'listening'
event.
On UNIX, the local domain is usually known as the UNIX domain. The path is a filesystem path name. It gets truncated to sizeof(sockaddr_un.sun_path)
bytes, decreased by 1. It varies on different operating system between 91 and 107 bytes. The typical values are 107 on Linux and 103 on OS X. The path is subject to the same naming conventions and permissions checks as would be done on file creation, will be visible in the filesystem, and will persist until unlinked.
On Windows, the local domain is implemented using a named pipe. The path must refer to an entry in \\?\pipe\
or \\.\pipe\
. Any characters are permitted, but the latter may do some processing of pipe names, such as resolving ..
sequences. Despite appearances, the pipe name space is flat. Pipes will not persist, they are removed when the last reference to them is closed. Do not forget JavaScript string escaping requires paths to be specified with double-backslashes, such as:
net.createServer().listen( path.join('\\\\?\\pipe', process.cwd(), 'myctl'));
The parameter backlog
behaves the same as in server.listen([port][, hostname][, backlog][, callback])
.
Note: The server.listen()
method may be called multiple times. Each subsequent call will re-open the server using the provided options.
Begin accepting connections on the specified port
and hostname
. If the hostname
is omitted, the server will accept connections on any IPv6 address (::
) when IPv6 is available, or any IPv4 address (0.0.0.0
) otherwise. Omit the port argument, or use a port value of 0
, to have the operating system assign a random port, which can be retrieved by using server.address().port
after the 'listening'
event has been emitted.
Backlog is the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog
and somaxconn
on Linux. The default value of this parameter is 511 (not 512).
This function is asynchronous. When the server has been bound, 'listening'
event will be emitted. The last parameter callback
will be added as a listener for the 'listening'
event.
One issue some users run into is getting EADDRINUSE
errors. This means that another server is already running on the requested port. One way of handling this would be to wait a second and then try again:
server.on('error', (e) => { if (e.code == 'EADDRINUSE') { console.log('Address in use, retrying...'); setTimeout(() => { server.close(); server.listen(PORT, HOST); }, 1000); } });
(Note: All sockets in Node.js are set SO_REUSEADDR
.)
Note: The server.listen()
method may be called multiple times. Each subsequent call will re-open the server using the provided options.
A Boolean indicating whether or not the server is listening for connections.
Set this property to reject connections when the server's connection count gets high.
It is not recommended to use this option once a socket has been sent to a child with child_process.fork()
.
Opposite of unref
, calling ref
on a previously unref
d server will not let the program exit if it's the only server left (the default behavior). If the server is ref
d calling ref
again will have no effect.
Calling unref
on a server will allow the program to exit if this is the only active server in the event system. If the server is already unref
d calling unref
again will have no effect.
This object is an abstraction of a TCP or local socket. net.Socket
instances implement a duplex Stream interface. They can be created by the user and used as a client (with connect()
) or they can be created by Node.js and passed to the user through the 'connection'
event of a server.
Construct a new socket object.
options
is an object with the following defaults:
{ fd: null, allowHalfOpen: false, readable: false, writable: false }
fd
allows you to specify the existing file descriptor of socket. Set readable
and/or writable
to true
to allow reads and/or writes on this socket (NOTE: Works only when fd
is passed). About allowHalfOpen
, refer to net.createServer()
and 'end'
event.
net.Socket
instances are EventEmitter
with the following events:
had_error
<boolean> true
if the socket had a transmission error.Emitted once the socket is fully closed. The argument had_error
is a boolean which says if the socket was closed due to a transmission error.
Emitted when a socket connection is successfully established. See connect()
.
Emitted when data is received. The argument data
will be a Buffer
or String
. Encoding of data is set by socket.setEncoding()
. (See the Readable Stream section for more information.)
Note that the data will be lost if there is no listener when a Socket
emits a 'data'
event.
Emitted when the write buffer becomes empty. Can be used to throttle uploads.
See also: the return values of socket.write()
Emitted when the other end of the socket sends a FIN packet.
By default (allowHalfOpen == false
) the socket will destroy its file descriptor once it has written out its pending write queue. However, by setting allowHalfOpen == true
the socket will not automatically end()
its side allowing the user to write arbitrary amounts of data, with the caveat that the user is required to end()
their side now.
Emitted when an error occurs. The 'close'
event will be called directly following this event.
Emitted after resolving the hostname but before connecting. Not applicable to UNIX sockets.
err
<Error> | <null> The error object. See dns.lookup()
.address
<string> The IP address.family
<string> | <null> The address type. See dns.lookup()
.host
<string> The hostname.Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.
See also: socket.setTimeout()
Returns the bound address, the address family name and port of the socket as reported by the operating system. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }
net.Socket
has the property that socket.write()
always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket - the network connection simply might be too slow. Node.js will internally queue up the data written to a socket and send it out over the wire when it is possible. (Internally it is polling on the socket's file descriptor for being writable).
The consequence of this internal buffering is that memory may grow. This property shows the number of characters currently buffered to be written. (Number of characters is approximately equal to the number of bytes to be written, but the buffer may contain strings, and the strings are lazily encoded, so the exact number of bytes is not known.)
Users who experience large or growing bufferSize
should attempt to "throttle" the data flows in their program with pause()
and resume()
.
The amount of received bytes.
The amount of bytes sent.
Opens the connection for a given socket.
For TCP sockets, options
argument should be an object which specifies:
port
: Port the client should connect to (Required).
host
: Host the client should connect to. Defaults to 'localhost'
.
localAddress
: Local interface to bind to for network connections.
localPort
: Local port to bind to for network connections.
family
: Version of IP stack. Defaults to 4
.
hints
: dns.lookup()
hints. Defaults to 0
.
lookup
: Custom lookup function. Defaults to dns.lookup
.
For local domain sockets, options
argument should be an object which specifies:
path
: Path the client should connect to (Required).For either case:
Normally this method is not needed, as net.createConnection
opens the socket. Use this only if you are implementing a custom Socket.
This function is asynchronous. When the 'connect'
event is emitted the socket is established. If there is a problem connecting, the 'connect'
event will not be emitted, the 'error'
event will be emitted with the exception.
The connectListener
parameter will be added as a listener for the 'connect'
event.
As socket.connect(options[, connectListener])
, with options as either {port: port, host: host}
or {path: path}
.
If true
- socket.connect(options[, connectListener])
was called and haven't yet finished. Will be set to false
before emitting connect
event and/or calling socket.connect(options[, connectListener])
's callback.
Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).
If exception
is specified, an 'error'
event will be emitted and any listeners for that event will receive exception
as an argument.
A Boolean value that indicates if the connection is destroyed or not. Once a connection is destroyed no further data can be transferred using it.
Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.
If data
is specified, it is equivalent to calling socket.write(data, encoding)
followed by socket.end()
.
The string representation of the local IP address the remote client is connecting on. For example, if you are listening on '0.0.0.0'
and the client connects on '192.168.1.1'
, the value would be '192.168.1.1'
.
The numeric representation of the local port. For example, 80
or 21
.
Pauses the reading of data. That is, 'data'
events will not be emitted. Useful to throttle back an upload.
Opposite of unref
, calling ref
on a previously unref
d socket will not let the program exit if it's the only socket left (the default behavior). If the socket is ref
d calling ref
again will have no effect.
The string representation of the remote IP address. For example, '74.125.127.100'
or '2001:4860:a005::68'
. Value may be undefined
if the socket is destroyed (for example, if the client disconnected).
The string representation of the remote IP family. 'IPv4'
or 'IPv6'
.
The numeric representation of the remote port. For example, 80
or 21
.
Resumes reading after a call to pause()
.
Set the encoding for the socket as a Readable Stream. See stream.setEncoding()
for more information.
Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket. enable
defaults to false
.
Set initialDelay
(in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting 0 for initialDelay will leave the value unchanged from the default (or previous) setting. Defaults to 0
.
Disables the Nagle algorithm. By default TCP connections use the Nagle algorithm, they buffer data before sending it off. Setting true
for noDelay
will immediately fire off data each time socket.write()
is called. noDelay
defaults to true
.
Sets the socket to timeout after timeout
milliseconds of inactivity on the socket. By default net.Socket
do not have a timeout.
When an idle timeout is triggered the socket will receive a 'timeout'
event but the connection will not be severed. The user must manually end()
or destroy()
the socket.
If timeout
is 0, then the existing idle timeout is disabled.
The optional callback
parameter will be added as a one-time listener for the 'timeout'
event.
Calling unref
on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unref
d calling unref
again will have no effect.
Sends data on the socket. The second parameter specifies the encoding in the case of a string--it defaults to UTF8 encoding.
Returns true
if the entire data was flushed successfully to the kernel buffer. Returns false
if all or part of the data was queued in user memory. 'drain'
will be emitted when the buffer is again free.
The optional callback
parameter will be executed when the data is finally written out - this may not be immediately.
A factory function, which returns a new net.Socket
and automatically connects with the supplied options
.
The options are passed to both the net.Socket
constructor and the socket.connect
method.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
Here is an example of a client of the previously described echo server:
const net = require('net'); const client = net.connect({port: 8124}, () => { // 'connect' listener console.log('connected to server!'); client.write('world!\r\n'); }); client.on('data', (data) => { console.log(data.toString()); client.end(); }); client.on('end', () => { console.log('disconnected from server'); });
To connect on the socket /tmp/echo.sock
the second line would just be changed to
const client = net.connect({path: '/tmp/echo.sock'});
A factory function, which returns a new unix net.Socket
and automatically connects to the supplied path
.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
A factory function, which returns a new net.Socket
and automatically connects to the supplied port
and host
.
If host
is omitted, 'localhost'
will be assumed.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
A factory function, which returns a new net.Socket
and automatically connects with the supplied options
.
The options are passed to both the net.Socket
constructor and the socket.connect
method.
Passing timeout
as an option will call socket.setTimeout()
after the socket is created, but before it is connecting.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
Following is an example of a client of the echo server described in the net.createServer()
section:
const net = require('net'); const client = net.createConnection({port: 8124}, () => { //'connect' listener console.log('connected to server!'); client.write('world!\r\n'); }); client.on('data', (data) => { console.log(data.toString()); client.end(); }); client.on('end', () => { console.log('disconnected from server'); });
To connect on the socket /tmp/echo.sock
the second line would just be changed to
const client = net.connect({path: '/tmp/echo.sock'});
A factory function, which returns a new unix net.Socket
and automatically connects to the supplied path
.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
A factory function, which returns a new net.Socket
and automatically connects to the supplied port
and host
.
If host
is omitted, 'localhost'
will be assumed.
The connectListener
parameter will be added as a listener for the 'connect'
event once.
Creates a new server. The connectionListener
argument is automatically set as a listener for the 'connection'
event.
options
is an object with the following defaults:
{ allowHalfOpen: false, pauseOnConnect: false }
If allowHalfOpen
is true
, then the socket won't automatically send a FIN packet when the other end of the socket sends a FIN packet. The socket becomes non-readable, but still writable. You should call the end()
method explicitly. See 'end'
event for more information.
If pauseOnConnect
is true
, then the socket associated with each incoming connection will be paused, and no data will be read from its handle. This allows connections to be passed between processes without any data being read by the original process. To begin reading data from a paused socket, call resume()
.
Here is an example of an echo server which listens for connections on port 8124:
const net = require('net'); const server = net.createServer((c) => { // 'connection' listener console.log('client connected'); c.on('end', () => { console.log('client disconnected'); }); c.write('hello\r\n'); c.pipe(c); }); server.on('error', (err) => { throw err; }); server.listen(8124, () => { console.log('server bound'); });
Test this by using telnet
:
$ telnet localhost 8124
To listen on the socket /tmp/echo.sock
the third line from the last would just be changed to
server.listen('/tmp/echo.sock', () => { console.log('server bound'); });
Use nc
to connect to a UNIX domain socket server:
$ nc -U /tmp/echo.sock
Tests if input is an IP address. Returns 0 for invalid strings, returns 4 for IP version 4 addresses, and returns 6 for IP version 6 addresses.
Returns true if input is a version 4 IP address, otherwise returns false.
Returns true if input is a version 6 IP address, otherwise returns false.
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https://nodejs.org/dist/latest-v6.x/docs/api/net.html