UDP Component

Properties   Methods   Events   Config Settings   Errors  

The User Datagram Protocol (UDP) component is used to facilitate UDP (datagram) communications. It can act both as a client and a server and communicate with any number of hosts simultaneously, as well as generate and receive broadcast packets.

Syntax

TipwUDP

Remarks

The interface of the component is similar to the interface of TCPClient, only much simpler. The component is activated or deactivated through the Active property. This property enables or disables sends or receives. The data can be sent in the same way as TCPClient, using the Send method and specifying the text to send. The destination is specified using the RemoteHost and RemotePort properties. Inbound data are received through the DataIn event.

If the UseConnection configuration setting is set to True, then a local association is created with the remote host. Otherwise, the component can receive datagrams (packets) from any host, and send datagrams to any host. Packets can be broadcast on the local net by setting the destination (RemoteHost) to 255.255.255.255.

The operation of the component is almost completely asynchronous. All calls, except the ones that deal with domain name resolution, operate through Windows messages (no blocking calls). The gain in performance is considerable when compared to using blocking calls.

Property List

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

AcceptData Property (UDP Component)

This property indicates whether data reception is currently enabled.

Syntax

property AcceptData: Boolean read get_AcceptData;

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 (UDP Component)

This property indicates whether the component is active.

Syntax

property Active: Boolean read get_Active;

Default Value

false

Remarks

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

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

DontRoute Property (UDP Component)

If this property is set to True, it forces the socket to send data directly to the interface (no routing).

Syntax

property DontRoute: Boolean read get_DontRoute write set_DontRoute;

Default Value

false

Remarks

If this property is set to True, it forces the socket to send data directly to the interface (no routing). Normally, IP sockets send packets of data through routers and gateways until they reach the final destination. If this property is set to True, then data will be delivered on the local subnet only.

This property is not available at design time.

LocalHost Property (UDP Component)

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

Syntax

property LocalHost: String read get_LocalHost write set_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 component initiate connections (or accept in the case of server components) 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 component 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 (UDP Component)

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

Syntax

property LocalPort: Integer read get_LocalPort write set_LocalPort;

Default Value

0

Remarks

The LocalPort property must be set before UDP is activated (Active is set to True). This instructs the component to bind to a specific port (or communication endpoint) in the local machine.

Setting it to 0 (default) enables the Transmission Control Protocol (TCP)/IP stack to choose a port at random. The chosen port will be shown by the LocalPort property after the connection is established.

LocalPort cannot be changed once the component is Active. Any attempt to set the LocalPort property when the component is Active will generate an error.

The LocalPort property is useful when trying to connect to services that require a trusted port on the client side.

RemoteHost Property (UDP Component)

This property includes the address of the remote host. Domain names are resolved to IP addresses.

Syntax

property RemoteHost: String read get_RemoteHost write set_RemoteHost;

Default Value

''

Remarks

The RemoteHost property specifies the IP address (IP number in dotted internet format) or domain name of the remote host.

If RemoteHost is set to 255.255.255.255, the component broadcasts data on the local subnet.

If the RemoteHost property is set to a domain name, a DNS request is initiated, and upon successful termination of the request, the RemoteHost property is set to the corresponding address. If the search is not successful, an error is returned.

If UseConnection is set to True, the RemoteHost must be set before the component is activated (Active is set to True).

RemotePort Property (UDP Component)

This property specifies the User Datagram Protocol (UDP) port in the remote host.

Syntax

property RemotePort: Integer read get_RemotePort write set_RemotePort;

Default Value

0

Remarks

The RemotePort is the UDP port on the RemoteHost to send UDP datagrams to.

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

If UseConnection is set to True, the RemotePort must be set before the component is activated (Active is set to True).

TimeToLive Property (UDP Component)

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

Syntax

property TimeToLive: Integer read get_TimeToLive write set_TimeToLive;

Default Value

0

Remarks

The default value for this property is 0, which tells the component to use the default time-to-live (TTL) value of the underlying Transmission Control Protocol (TCP)/IP subsystem. Depending on the application, you can specify a value between 1 and 255.

Activate Method (UDP Component)

This method enables sending and receiving of data.

Syntax

procedure 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) messages. This method must be called before using the component to send and receive data.

If the UseConnection configuration setting is set to True, then a local association (connection) to the remote host is also created.

Config Method (UDP Component)

Sets or retrieves a configuration setting.

Syntax

function Config(ConfigurationString: String): String;

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the component, 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 (UDP Component)

This method disables sending and receive of data.

Syntax

procedure 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 (UDP Component)

This method processes events from the internal message queue.

Syntax

procedure DoEvents();

Remarks

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

PauseData Method (UDP Component)

This method pauses data reception.

Syntax

procedure 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 (UDP Component)

This method reenables data reception after a call to PauseData .

Syntax

procedure 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 (UDP Component)

This method will reset the component.

Syntax

procedure Reset();

Remarks

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

ResolveRemoteHost Method (UDP Component)

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

Syntax

procedure 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 component will resolve the hostname automatically when needed. If DelayHostResolution is True, this method may be called to manually resolve RemoteHost, if desired.

Send Method (UDP Component)

This method sends binary data to the remote host.

Syntax

procedure Send(Text: TBytes);

Remarks

This method sends the specified binary data to the remote host. To send text, use the SendText method instead.

Example. Send Data:

UDPControl.LocalPort = 8765 UDPControl.RemotePort = 8765 UDPControl.RemoteHost = "HostNameOrIPAddress" UDPControl.Active = True UDPControl.SendText("Hello!")

SendBytes Method (UDP Component)

This method sends binary data to the remote host.

Syntax

procedure SendBytes(Data: TBytes);

Remarks

This method sends the specified binary data to the remote host. To send text, use the SendText method instead.

Example. Send Data:

UDPControl.LocalPort = 8765 UDPControl.RemotePort = 8765 UDPControl.RemoteHost = "HostNameOrIPAddress" UDPControl.Active = True UDPControl.SendText("Hello!")

SendText Method (UDP Component)

This method sends text to the remote host.

Syntax

procedure SendText(Text: String);

Remarks

This method sends the specified text to the remote host. To send binary data, use the SendBytes method instead.

Example. Send Data:

UDPControl.LocalPort = 8765 UDPControl.RemotePort = 8765 UDPControl.RemoteHost = "HostNameOrIPAddress" UDPControl.Active = True UDPControl.SendText("Hello!")

DataIn Event (UDP Component)

This event is fired when data are received.

Syntax

type TDataInEvent = procedure (
  Sender: TObject;
  const Datagram: String;
  const DatagramB: TBytes;
  const SourceAddress: String;
  SourcePort: Integer
) of Object;

property OnDataIn: TDataInEvent read FOnDataIn write FOnDataIn;

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 (UDP Component)

Fired when information is available about errors during data delivery.

Syntax

type TErrorEvent = procedure (
  Sender: TObject;
  ErrorCode: Integer;
  const Description: String
) of Object;

property OnError: TErrorEvent read FOnError write FOnError;

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the component raises 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 (UDP Component)

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

Syntax

type TReadyToSendEvent = procedure (
  Sender: TObject
) of Object;

property OnReadyToSend: TReadyToSendEvent read FOnReadyToSend write FOnReadyToSend;

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 (UDP Component)

The component 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 component, access to these internal properties is provided through the Config method.

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (UDP Component)

UDP Errors

SSL Errors

TCP/IP Errors