UDP Component

Properties   Methods   Events   Config Settings   Errors  

The 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/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. This is identical to assigning data to the DataToSend property. The destination is specified using the RemoteHost and RemotePort properties. Inbound data is received through the DataIn event.

If the UseConnection config 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 enables or disables data reception (the DataIn event).

Syntax

property AcceptData: Boolean read get_AcceptData write set_AcceptData;

Default Value

true

Remarks

This property enables or disables data reception (the DataIn event). Setting this property to False, temporarily disables data reception (and the DataIn event). Setting this property to True, reenables data reception.

Note: It is recommended to use the PauseData or ProcessData method instead of setting this property.

This property is not available at design time.

Active Property (UDP Component)

Indicates whether the component is active.

Syntax

property Active: Boolean read get_Active write set_Active;

Default Value

false

Remarks

This property indicates whether the component is currently active and can send or receive data.

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

Note: Use the Activate or Deactivate method to control whether the component is active.

This property is not available at design time.

DataToSend Property (UDP Component)

A string of data to be sent to the remote host. Write-only property.

Syntax

property DataToSend: String write set_DataToSend;
property DataToSendB: TBytes write set_DataToSendB;

Default Value

''

Remarks

Assigning a string to the DataToSend property makes the component send the string to the remote host. The Send method provides similar functionality.

Attempts to send the string assigned to DataToSend as a complete message. If system buffers are full, or the message cannot be delivered for any other reason, an error is fired, and no portion of the message is sent. This is different from TCP where portions of the messages can be sent. UDP sends either a complete message or nothing at all.

If you are sending data to the remote host faster than it can process it, or faster than the network's bandwidth allows, the outgoing queue might fill up. When this happens, DataToSend raises the exception with errorcode 10035 and message '[10035] Operation would block' (WSAEWOULDBLOCK). You can handle this exception, and then try to send the data again.

Example (Send Data)

UDPControl.LocalPort = 8765 UDPControl.RemotePort = 8765 UDPControl.RemoteHost = "HostNameOrIPAddress" UDPControl.Active = True UDPControl.DataToSend = "Hello!"

This property is write-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

The LocalHost 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 multi-homed hosts (machines with more than one IP interface) setting LocalHost to the value of an interface will make the component initiate connections (or accept in the case of server components) only through that interface.

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 multi-homed 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)

The 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). It instructs the component to bind to a specific port (or communication endpoint) in the local machine.

Setting it to 0 (default) enables the 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 in the client side.

RemoteHost Property (UDP Component)

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)

The 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)

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 TTL value of the underlying TCP/IP subsystem. Depending on the application, you can specify a value between 1 and 255.

Activate Method (UDP Component)

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) which can be used for sending and receiving 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)

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)

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)

Reset the component.

Syntax

procedure Reset();

Remarks

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

ResolveRemoteHost Method (UDP Component)

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 necessary. If DelayHostResolution is True this method may be called to manually resolve RemoteHost if desired.

Send Method (UDP Component)

Send data to the remote host.

Syntax

procedure Send(Text: TBytes);

Remarks

Calling this method is equivalent to setting the DataToSend property to Text.

Example (Send Data)

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

SendBytes Method (UDP Component)

Send data to the remote host.

Syntax

procedure SendBytes(Data: TBytes);

Remarks

Calling this method is equivalent to call SendBytes/SendText method.

Example (Send Data)

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

SendText Method (UDP Component)

Send data to the remote host.

Syntax

procedure SendText(Text: String);

Remarks

Calling this method is equivalent to call SendBytes/SendText method.

Example (Send Data)

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

DataIn Event (UDP Component)

Fired when data is received.

Syntax

type TDataInEvent = procedure (
  Sender: TObject;
  Datagram: String;
  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)

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 TCP/IP subsystem is ready to accept data after a failed DataToSend.

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

	104   UDP is already Active.
	106   You cannot change the LocalPort while the component is Active.
	107   You cannot change the LocalHost at this time. A connection is in progress.
	109   The component must be Active for this operation.
	112   Cannot change MaxPacketSize while the component is Active.
	113   Cannot change ShareLocalPort option while the component is Active.
	114   Cannot change RemoteHost when UseConnection is set and the component Active.
	115   Cannot change RemotePort when UseConnection is set and the component is Active.
	116   RemotePort can't be zero when UseConnection is set. Please specify a valid service port number.
	117   Cannot change UseConnection while the component is Active.
	118   Message can't be longer than MaxPacketSize.
	119   Message too short.
	434   Unable to convert string to selected CodePage

SSL Errors

	270   Cannot load specified security library.
	271   Cannot open certificate store.
	272   Cannot find specified certificate.
	273   Cannot acquire security credentials.
	274   Cannot find certificate chain.
	275   Cannot verify certificate chain.
	276   Error during handshake.
	280   Error verifying certificate.
	281   Could not find client certificate.
	282   Could not find server certificate.
	283   Error encrypting data.
	284   Error decrypting data.

TCP/IP Errors

	10004   [10004] Interrupted system call.
	10009   [10009] Bad file number.
	10013   [10013] Access denied.
	10014   [10014] Bad address.
	10022   [10022] Invalid argument.
	10024   [10024] Too many open files.
	10035   [10035] Operation would block.
	10036   [10036] Operation now in progress.
	10037   [10037] Operation already in progress.
	10038   [10038] Socket operation on non-socket.
	10039   [10039] Destination address required.
	10040   [10040] Message too long.
	10041   [10041] Protocol wrong type for socket.
	10042   [10042] Bad protocol option.
	10043   [10043] Protocol not supported.
	10044   [10044] Socket type not supported.
	10045   [10045] Operation not supported on socket.
	10046   [10046] Protocol family not supported.
	10047   [10047] Address family not supported by protocol family.
	10048   [10048] Address already in use.
	10049   [10049] Can't assign requested address.
	10050   [10050] Network is down.
	10051   [10051] Network is unreachable.
	10052   [10052] Net dropped connection or reset.
	10053   [10053] Software caused connection abort.
	10054   [10054] Connection reset by peer.
	10055   [10055] No buffer space available.
	10056   [10056] Socket is already connected.
	10057   [10057] Socket is not connected.
	10058   [10058] Can't send after socket shutdown.
	10059   [10059] Too many references, can't splice.
	10060   [10060] Connection timed out.
	10061   [10061] Connection refused.
	10062   [10062] Too many levels of symbolic links.
	10063   [10063] File name too long.
	10064   [10064] Host is down.
	10065   [10065] No route to host.
	10066   [10066] Directory not empty
	10067   [10067] Too many processes.
	10068   [10068] Too many users.
	10069   [10069] Disc Quota Exceeded.
	10070   [10070] Stale NFS file handle.
	10071   [10071] Too many levels of remote in path.
	10091   [10091] Network subsystem is unavailable.
	10092   [10092] WINSOCK DLL Version out of range.
	10093   [10093] Winsock not loaded yet.
	11001   [11001] Host not found.
	11002   [11002] Non-authoritative 'Host not found' (try again or check DNS setup).
	11003   [11003] Non-recoverable errors: FORMERR, REFUSED, NOTIMP.
	11004   [11004] Valid name, no data record (check DNS setup).