NetBIOS session implementation written in JavaScript
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Latest commit 7102849 Mar 13, 2013


A 100% javascript implemention of the NetBIOS session protocol defined in RFC1001 and RFC1002.

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var Session = require('netbios-session')
var net = require('net');

var NAME = null;

var server = net.createServer(function(socket) {
  console.log('---> new connection from [' + socket.remoteAddress + ']');
  var session = new Session();
  session.attach(socket, function(error, request) {
    if (error) {
      console.log('---> attach error [' + error + ']');

    console.log('---> new call to [' + request.callTo + '] from [' +
                request.callFrom + ']');

    if (NAME && !== NAME) {
      console.log('---> rejecting');
      request.reject('Not listening on called name');

    session.on('message', function(msg) {
      console.log('---> received a message with [' + msg.length + '] bytes');

    console.log('---> accepting');

server.listen(139, function() {
  console.log('server started');


This module provides a useful set of functionality from the RFCs, but it is still a work in progress.

Please be aware of the following limitations:

  • Currently the code does not support session retargeting. This can be used to instruct a client to close its current connection and try again at a different address. Currently redirection responses are ignored.
  • The API should be considered unstable as it may change in future versions.

Feedback, testing help, and pull requests welcome.

Class: NetbiosSession

The NetbiosSession class represents a message based session with a remote host. There is an initial session negotiation process that requires the caller to request a new session for a particular name. The other peer can then accept or reject the request. Once a request has been accepted the session is considered to be connected. At this point messages can be sent and received.

NetbiosSession inherits from [EventEmitter][] class.

new NetbiosSession(options)

Create a new NetbiosSession instance with the given options.

  • options {Object | null} Optional configuration options for the session. Possible values are:
    • autoAccept {Boolean} If set to true, then the session will default to accepting all requests if an attach() callback is not provided. Default value is false
    • direct {Boolean} Use direct connection mode if this option is set. This means that the session establishment handshake should not be performed. Instead, consider the session connected as soon as we have a valid TCP socket. This is useful for protocols like SMB that still want a NetBIOS message header, but do not use the request/response commands.
    • paused {Boolean} If set the session will start in the paused condition. This means that the session can connect or attach as needed, but no 'message' events will occur until resume() is called.

session.attach(socket, callback)

Attach the session to a net.Socket instance and wait to receive an incoming NetBIOS session request. This is typically used to handle in the net.Server 'connection' event.

If provided, the callback will be called when the request is initiated. It is also important for the callback implementation to either accept or reject the request. This is done by calling request.accept() or request.reject(). If neither of these methods is called, then the session request negotiation process will stall. If a callback is not provided, then the default policy will be used to either reject or accept.

  • socket {Socket Object} The socket to attach to. This socket should already be bound and connected.
  • callback {Function | null} An optional callback that is used to signal that a request has occured and to approve or deny the request. NOTE: If the direct option was set in the session constructor, then this callback will not be called.
    • error {Error Object} Provided if an error occurs during the attachment.
    • request {Object} An object describing the session request and providing method to allow the callback to accept() or reject() the request. NOTE: One of these methods must be called.
      • callTo {NetbiosName} The NetbiosName object representing the service the session is trying to connect to.
      • callFrom {NetbiosName} The NetbiosName object representing the service that is initiating the session.
      • accept {Function} Call this method to accept the request and allow the session to proceed. Can be called asynchronously
      • reject {Function} Call this method to reject the request and to close the underlying socket. A reason string can optionally be provided. The reject() method can be called asynchronously.
        • reason {String | null} A string from an enumerated list of values that can optionally be provided. If not specified then Unspecified error is used. See below for other valid reasons.

Valid reason strings are:

  • 'Not listening on called name'
  • 'Not listening for calling name'
  • 'Called name not present'
  • 'Called name present, but insufficient resources'
  • 'Unspecified error'

session.connect(port, host, callTo, callFrom, callback)

Initiate a new NetBIOS session with a remote host. This method will open a new socket and connect to the given host and port. A session will then be requested for the given callTo name coming from the given callFrom name. These must be NetbiosName object instances. The remote host can then accept or reject the session based on the names provided. The callback will be called once the connection successfully completes or has been rejected.

  • port {Number} The remote port number to connect to. Normally this should be port 139 for most NetBIOS session servers.
  • host {String} The remote host name to connect to.
  • callTo {NetbiosName Object} The NetbiosName representing the service you are trying to connect to.
  • callFrom {NetbiosName Object} The NetbiosName representing the local service initiating the session.
  • callback {Function | null} The function that will be called once both the underlying socket and the session have fully connected.
    • error {Error Object | null} If an error occurred it will be passed. If the connection was rejected, then error will be set with the result code provided by the remote host.

session.write(msg, callback)

Write the given msg out to the remote session peer. If the message can be fully flushed to the kernel, then write() will return true. If false is returned, you should wait until the next 'drain' event before writing more data to the session.

  • msg {Buffer Object} The message Buffer to send to the remote session peer. Note, the message can be at most NetbiosSession.MAX_MESSAGE_LENGTH bytes long.
  • callback {Function | null} Optional function that will be called once the msg object has been written out or when an error occurs.
    • error {Error Object | null} The error that occurred, if any.


Stop accepting messages from the remote session peer. This can be used to implement back pressure if the messages are coming too fast. Note, the session can still negotiate the connection even if paused, so there may still be network traffic if the session is not yet connected.


Resume accepting message from the remote session peer.

Constant: session.MAX_MESSAGE_LENGTH

Maximum number of bytes that can be passed to a single write() method call to be sent as a message. Also, messages received will not exceed this limit as well.

Event: 'connect'

When the NetbiosSession has negotiated and established a new session, the 'connect' event will be emitted.

Event: 'message'

Whenever a message is received from the remote session peer, a 'message' event will be emitted.

  • msg {Buffer Object} A Buffer containing the message received.

Event: 'end'

The 'end' event is emitted when the session can no longer send or receive messages.

Event: 'error'

The 'error' event is emitted when an error is encountered.

  • error {Error Object} The error that occured.