MCast Class

Properties   Methods   Events   Config Settings   Errors  

The MCast class is used to multicast User Datagram Protocol (UDP) datagrams to multicast-capable hosts in multicast-capable subnets. It can act both as a client and a server and can communicate with any number of hosts simultaneously, as well as generate and receive broadcast packets.

Syntax

ipworks.MCast

Remarks

The MCast class is very similar to UDP, except for some additional properties that provide support for multicast datagrams. To send datagrams to a multicast group, simply assign the address of the group to RemoteHost. To receive datagrams from one or more groups, assign the group addresses to MulticastGroup one by one (after the class is activated). TimeToLive allows you to specify how many subnets a packet should be allowed to receive. ReceiveInterface and SendInterface allow you to select the network interface for multicast operations.

The class is activated/deactivated through the Active property. This property enables or disables sends or receives. The data can be sent in the same way as UDP, by calling the Send method with a Text parameter. The destination is specified using the RemoteHost and RemotePort properties. Inbound data are received through the DataIn event.

Property List

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The following is the full list of the properties of the class with short descriptions. Click on the links for further details.

Method List

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The following is the full list of the methods of the class with short descriptions. Click on the links for further details.

Event List

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The following is the full list of the events fired by the class with short descriptions. Click on the links for further details.

Config Settings

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The following is a list of config settings for the class with short descriptions. Click on the links for further details.

AcceptData Property (MCast Class)

This property indicates whether data reception is currently enabled.

Syntax

public boolean isAcceptData();

Default Value

True

Remarks

This property indicates whether data reception is currently enabled. When false, data reception is disabled and the DataIn event will not fire. Use the PauseData and ProcessData methods to pause and resume data reception.

This property is read-only and not available at design time.

Active Property (MCast Class)

This property indicates whether the class is active.

Syntax

public boolean isActive();

Default Value

False

Remarks

This property indicates whether the class is currently active and can send or receive data. Use the Activate and Deactivate methods to control whether the class is active.

This property is read-only and not available at design time.

LocalHost Property (MCast Class)

The name of the local host or user-assigned IP interface through which connections are initiated or accepted.

Syntax

public String getLocalHost();
public void setLocalHost(String localHost);

Default Value

""

Remarks

This property contains the name of the local host as obtained by the gethostname() system call, or if the user has assigned an IP address, the value of that address.

In multihomed hosts (machines with more than one IP interface) setting LocalHost to the IP address of an interface will make the class initiate connections (or accept in the case of server classs) only through that interface. It is recommended to provide an IP address rather than a hostname when setting this property to ensure the desired interface is used.

If the class is connected, the LocalHost property shows the IP address of the interface through which the connection is made in internet dotted format (aaa.bbb.ccc.ddd). In most cases, this is the address of the local host, except for multihomed hosts (machines with more than one IP interface).

Note: LocalHost is not persistent. You must always set it in code, and never in the property window.

LocalPort Property (MCast Class)

This property includes the User Datagram Protocol (UDP) port in the local host where MCast binds.

Syntax

public int getLocalPort();
public void setLocalPort(int localPort);

Default Value

0

Remarks

This property must be set before MCast is activated (Active is set to True). It instructs the class to bind to a specific port (or communication endpoint) on the local machine.

Setting it to 0 (default) enables the system to choose a port at random. The chosen port will be shown by this property after the connection is established.

This property cannot be changed once the class is Active. Any attempt to set this property when the class is Active will generate an error.

This property is useful when trying to send data to services that require a trusted port on the client side.

Loopback Property (MCast Class)

This property enables or disables loopback of data sent to the multicast group.

Syntax

public boolean isLoopback();
public void setLoopback(boolean loopback);

Default Value

True

Remarks

This property enables or disables loopback of data sent to the multicast group. Setting this property to False disables loopback of data sent through the class (normally loopback is enabled). This property is directly related to the IP_MULTICAST_LOOP socket option.

This property is not available at design time.

MulticastGroup Property (MCast Class)

This property includes the multicast group to join or leave.

Syntax

public String getMulticastGroup();
public void setMulticastGroup(String multicastGroup);

Default Value

""

Remarks

This property contains the multicast group to join or leave. Multicast groups are joined by assigning values to this property after the class is activated. More than one group may be joined at the same time. To define which interface to use, the ReceiveInterface property is used.

Determining whether a group is left or joined is done by setting the first letter of MulticastGroup to "-" or "+". The default operation is join.

To remove the class from a multicast group once it is joined, simply assign this groupname (address) to MulticastGroup prefixed by a minus sign "-".

Example. Joining/Leaving Groups:

MCastControl.Active = true MCastControl.MulticastGroup = "+231.31.31.31" MCastControl.MulticastGroup = "+232.32.32.32" MCastControl.MulticastGroup = "-232.32.32.32" MCastControl.MulticastGroup = "-231.31.31.31"

ReceiveInterface Property (MCast Class)

This property includes the interface with which to receive multicast packets. If empty, the default is used.

Syntax

public String getReceiveInterface();
public void setReceiveInterface(String receiveInterface);

Default Value

""

Remarks

This property is useful when there is more than one network interface, and the one used for receiving multicast datagrams is not the default. If you wish to set an interface other than the system default, provide the IP address of the interface to be set.

This property is used along with the MulticastGroup property to join one or more multicast groups. The joining is done after the class is activated by assigning proper values to MulticastGroup.

This property is not available at design time.

RemoteHost Property (MCast Class)

This property includes the address of the remote host (multicast group).

Syntax

public String getRemoteHost();
public void setRemoteHost(String remoteHost);

Default Value

""

Remarks

This property contains the address of the remote host (multicast group). To send a multicast datagram, specify a RemoteHost value in the range of 224.0.0.0 to 239.255.255.255. These addresses are reserved as multicast addresses by IP.

RemotePort Property (MCast Class)

This property includes the User Datagram Protocol (UDP) port on the remote host.

Syntax

public int getRemotePort();
public void setRemotePort(int remotePort);

Default Value

0

Remarks

This property contains the UDP port on the RemoteHost to send UDP datagrams to.

A valid port number (i.e., a value between 1 and 65535) is required.

SendInterface Property (MCast Class)

This property includes the interface from which multicast packets are sent. If empty, the default is used.

Syntax

public String getSendInterface();
public void setSendInterface(String sendInterface);

Default Value

""

Remarks

This property is useful when there is more than one network interface, and the one used for sending multicast datagrams is not the default. If you wish to set an interface other than the system default, provide the IP address of the interface to be set.

This property is not available at design time.

TimeToLive Property (MCast Class)

This property includes the maximum number of subnets that a multicast datagram can traverse.

Syntax

public int getTimeToLive();
public void setTimeToLive(int timeToLive);

Default Value

7

Remarks

This property contains the maximum number of subnets that a multicast datagram can traverse. The default value for this property is 7. This is an arbitrary value. You need to specify a value suitable for your application.

Multicast datagrams with this property set to 0 are not transmitted on any subnetwork. Multicast datagrams with this property set to 1 are delivered only on the local network. Multicast datagrams with this property set to greater than 1 may be delivered to more than one subnetwork if one or more multicast routers are attached to the first-hop subnetwork.

A multicast router does not forward multicast datagrams with destination addresses between 224.0.0.0 and 224.0.0.255, inclusive, regardless of their TimeToLive. This particular range of addresses is reserved for the use of routing protocols and other low-level topology discovery or maintenance protocols, such as gateway discovery and group membership reporting.

Activate Method (MCast Class)

This method enables sending and receiving of data.

Syntax

public void activate();

Remarks

This method enables sending and receiving of data. When called, the component will create a communication endpoint (socket) that can be used for sending and receiving User Datagram Protocol (UDP) datagrams.

Config Method (MCast Class)

Sets or retrieves a configuration setting.

Syntax

public String config(String configurationString);

Remarks

Config is a generic method available in every class. It is used to set and retrieve configuration settings for the class.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the Config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

Deactivate Method (MCast Class)

This method disables sending and receiving of data.

Syntax

public void deactivate();

Remarks

This method disables sending and receiving of data. When called, the component will destroy the existing socket and disable data communications.

DoEvents Method (MCast Class)

This method processes events from the internal message queue.

Syntax

public void doEvents();

Remarks

When DoEvents is called, the class processes any available events. If no events are available, it waits for a preset period of time, and then returns.

PauseData Method (MCast Class)

This method pauses data reception.

Syntax

public void pauseData();

Remarks

This method pauses data reception when called. While data reception is paused, the DataIn event will not fire. Call ProcessData to reenable data reception.

ProcessData Method (MCast Class)

This method reenables data reception after a call to PauseData .

Syntax

public void processData();

Remarks

This method reenables data reception after a previous call to PauseData. When PauseData is called, the DataIn event will not fire. To reenable data reception and allow DataIn to fire, call this method.

Note: This method is used only after previously calling PauseData. It does not need to be called to process incoming data by default.

Reset Method (MCast Class)

This method resets the class.

Syntax

public void reset();

Remarks

This method will reset the class's properties to their default values.

ResolveRemoteHost Method (MCast Class)

This method resolves the hostname in RemoteHost to an IP address.

Syntax

public void resolveRemoteHost();

Remarks

This method resolves the hostname specified by RemoteHost to an IP address. The resolved value is available in the RemoteHost property after this method returns.

In most cases, calling this method is not necessary; the class will resolve the hostname automatically when needed. If DelayHostResolution is true, this method may be called to manually resolve RemoteHost, if desired.

Send Method (MCast Class)

This method sends data to the remote host.

Syntax

public void send(byte[] text);

Remarks

This method sends data to the remote host.

SendBytes Method (MCast Class)

This method sends data to the remote host.

Syntax

public void sendBytes(byte[] data);

Remarks

This method sends data to the remote host. Calling this method is equivalent to calling the SendBytes/SendText method.

SendText Method (MCast Class)

This method sends data to the remote host.

Syntax

public void sendText(String text);

Remarks

This method sends data to the remote host. Calling this method is equivalent to calling the SendBytes/SendText method.

DataIn Event (MCast Class)

This event is fired when data are received.

Syntax

public class DefaultMCastEventListener implements MCastEventListener {
  ...
  public void dataIn(MCastDataInEvent e) {}
  ...
}

public class MCastDataInEvent {
  public byte[] datagram;
  public String sourceAddress;
  public int sourcePort;
}

Remarks

The DataIn event is fired every time a new datagram is received.

Datagram contains the packet as sent by the remote host.

SourceAddress contains the IP number (Internet address) of the remote host, and SourcePort contains the port from which the packet originated.

Note: Events are not re-entrant. Performing time-consuming operations within this event will prevent it from firing again in a timely manner and may affect overall performance.

Error Event (MCast Class)

Fired when information is available about errors during data delivery.

Syntax

public class DefaultMCastEventListener implements MCastEventListener {
  ...
  public void error(MCastErrorEvent e) {}
  ...
}

public class MCastErrorEvent {
  public int errorCode;
  public String description;
}

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the class throws an exception.

The ErrorCode parameter contains an error code, and the Description parameter contains a textual description of the error. For a list of valid error codes and their descriptions, please refer to the Error Codes section.

ReadyToSend Event (MCast Class)

This event is fired when the class is ready to send data.

Syntax

public class DefaultMCastEventListener implements MCastEventListener {
  ...
  public void readyToSend(MCastReadyToSendEvent e) {}
  ...
}

public class MCastReadyToSendEvent {
}

Remarks

The ReadyToSend event indicates that the underlying Transmission Control Protocol (TCP)/IP subsystem is ready to accept data after a failed Send.

Config Settings (MCast Class)

The class accepts one or more of the following configuration settings. Configuration settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the Config method.

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (MCast Class)

MCast Errors

SSL Errors

TCP/IP Errors