XMLSocket class

Availability

Flash Player 5.

Description

The XMLSocket class implements client sockets that allow the computer running Flash Player to communicate with a server computer identified by an IP address or domain name. The XMLSocket class is useful for client-server applications that require low latency, such as real-time chat systems. A traditional HTTP-based chat solution frequently polls the server and downloads new messages using an HTTP request. In contrast, an XMLSocket chat solution maintains an open connection to the server, which allows the server to immediately send incoming messages without a request from the client.

To use the XMLSocket class, the server computer must run a daemon that understands the protocol used by the XMLSocket class. The protocol is as follows:

XML messages are sent over a full-duplex TCP/IP stream socket connection.
Each XML message is a complete XML document, terminated by a zero byte.
An unlimited number of XML messages can be sent and received over a single XMLSocket connection.

The following restrictions apply to how and where an XMLSocket object can connect to the server:

The XMLSocket.connect() method can connect only to TCP port numbers greater than or equal to 1024. One consequence of this restriction is that the server daemons that communicate with the XMLSocket object must also be assigned to port numbers greater than or equal to 1024. Port numbers below 1024 are often used by system services such as FTP, Telnet, and HTTP, thus XMLSocket objects are barred from these ports for security reasons. The port number restriction limits the possibility that these resources will be inappropriately accessed and abused.
The XMLSocket.connect() method can connect only to computers in the same domain where the SWF file resides. This restriction does not apply to SWF files running off a local disk. (This restriction is identical to the security rules for loadVariables(), XML.sendAndLoad(), and XML.load().) To connect to a server daemon running in a domain other than then one where the SWF resides, you can create a security policy file on the server that allows access from specific domains. For more information on creating policy files for XMLSocket connections, see About allowing cross-domain data loading.

Setting up a server to communicate with the XMLSocket object can be challenging. If your application does not require real-time interactivity, use the loadVariables() action, or Flash HTTP-based XML server connectivity (XML.load(), XML.sendAndLoad(), XML.send()), instead of the XMLSocket class.

To use the methods of the XMLSocket class, you must first use the constructor, new XMLSocket, to create a new XMLSocket object.

Method summary for the XMLSocket class

Method	Description
`XMLSocket.close()`	Closes an open socket connection.
`XMLSocket.connect()`	Establishes a connection to the specified server.
`XMLSocket.send()`	Sends an XML object to the server.

Event handler summary for the XMLSocket class

Event handler	Description
`XMLSocket.onClose()`	An event handler that is invoked when an XMLSocket connection is closed.
`XMLSocket.onConnect()`	An event handler that is invoked by Flash Player when a connection request initiated through `XMLSocket.connect()` has succeeded or failed.
`XMLSocket.onData()`	An event handler that is invoked when an XML message has been downloaded from the server.
`XMLSocket.onXML()`	An event handler that is invoked when an XML object arrives from the server.

Constructor for the XMLSocket class

Availability

Flash Player 5.

Usage

new XMLSocket()

Parameters

None.

Returns

Nothing.

Description

Constructor; creates a new XMLSocket object. The XMLSocket object is not initially connected to any server. You must call XMLSocket.connect() to connect the object to a server.