ICMP Component

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The ICMP component is used to facilitate ICMP communications. It can act both as a client and a server and can communicate with any number of hosts simultaneously. It also can generate and receive broadcast packets.

Syntax

TipwICMP

Remarks

The interface of the component is similar to the interface of TCPClient, only it is much simpler. The component is activated/deactivated by using the Active property. This property enables or disables the sending or receiving of data. Data can be sent in the same way as TCPClient, using the Send method and Text parameter. The destination is specified using the RemoteHost property. The component automatically creates an ICMP header containing MessageType, MessageSubType, and a checksum for the message.

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 can send datagrams to any host. Packets can be broadcast on the local net by setting the destination to 255.255.255.255.

Inbound data is received through the DataIn event.

The operation of the component is almost completely asynchronous. All the 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 with 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 (ICMP 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 (ICMP 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.

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

MessageSubType Property (ICMP Component)

This property is the subtype of the ICMP message (part of the ICMP header).

Syntax

property MessageSubType: Integer read get_MessageSubType write set_MessageSubType;

Default Value

0

Remarks

This property contains the subtype of the ICMP message (part of the ICMP header). The ICMP message subtype (also referred to as "code") is a byte value representing the message subclass. Its meaning is associated with the MessageType.

Types and subtypes of ICMP messages are defined in the various internet RFCs and other documentation associated with Transmission Control Protocol (TCP)/IP.

MessageType Property (ICMP Component)

This property includes the type of the ICMP message (part of the ICMP header).

Syntax

property MessageType: Integer read get_MessageType write set_MessageType;

Default Value

0

Remarks

This property contains the type of the ICMP message (part of the ICMP header). The ICMP message type is a byte value representing the message class. The message type defines the structure and meaning of the message data assigned to Text parameter of the Send method.

Types for ICMP messages are defined in the various internet RFCs and other documentation associated with Transmission Control Protocol (TCP/IP). The following are a few examples of ICMP message types:

RemoteHost Property (ICMP Component)

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

Syntax

property RemoteHost: String read get_RemoteHost write set_RemoteHost;

Default Value

''

Remarks

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

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

If this property is set to a domain name, a DNS request is initiated. Upon successful termination of the request, the property is set to the corresponding address. If the search is not successful, the component raises an exception.

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

Timeout Property (ICMP Component)

This property specifies the timeout for the component.

Syntax

property Timeout: Integer read get_Timeout write set_Timeout;

Default Value

0

Remarks

If the Timeout property is set to 0, all operations return immediately, potentially failing with an WOULDBLOCK error if data cannot be sent or received immediately.

If Timeout is set to a positive value, the component will automatically retry each operation that otherwise would result in a WOULDBLOCK error for a maximum of Timeout seconds.

The component will use DoEvents to enter an efficient wait loop during any potential waiting period, making sure that all system events are processed immediately as they arrive. This ensures that the host application does not freeze and remains responsive.

If Timeout expires, and the operation is not yet complete, the component raises an exception.

Note: By default, all timeouts are inactivity timeouts, that is, the timeout period is extended by Timeout seconds when any amount of data is successfully sent or received.

The default value for the Timeout property is 0 (asynchronous operation).

TimeToLive Property (ICMP Component)

This property includes the time-to-live (TTL) value for the ICMP packets sent by the component.

Syntax

property TimeToLive: Integer read get_TimeToLive write set_TimeToLive;

Default Value

0

Remarks

This method contains the time-to-live (TTL) value for the ICMP packets sent by the component. The TTL field of the ICMP packet is a counter limiting the lifetime of a packet.

Each router (or other module) that handles a packet decrements the TTL field by one or more if it holds the packet for more than one second. Thus, the TTL value is effectively a hop count limit on how far a datagram can propagate through the internet. When the TTL value is reduced to zero (or less), the packet is discarded.

If the value of the property is set to zero, then the default TTL value of the underlying Transmission Control Protocol (TCP)/IP subsystem will be used.

This property is not available at design time.

Activate Method (ICMP 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 ICMP 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 also is created.

Config Method (ICMP 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 (ICMP Component)

This method disables sending and receiving 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 (ICMP 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 (ICMP 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 (ICMP 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 (ICMP 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 (ICMP 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 (ICMP Component)

This method sends data to the remote host.

Syntax

procedure Send(Text: TBytes);

Remarks

This method sends data to the remote host.

SendBytes Method (ICMP Component)

This method sends data to the remote host.

Syntax

procedure SendBytes(Data: TBytes);

Remarks

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

SendText Method (ICMP Component)

This method sends data to the remote host.

Syntax

procedure SendText(Text: String);

Remarks

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

DataIn Event (ICMP Component)

This event is fired when a new ICMP messages come in.

Syntax

type TDataInEvent = procedure (
  Sender: TObject;
  MessageType: Integer;
  MessageSubType: Integer;
  const MessageData: String;
  const MessageDataB: TBytes;
  Checksum: Integer;
  const SourceAddress: String
) of Object;

property OnDataIn: TDataInEvent read FOnDataIn write FOnDataIn;

Remarks

The MessageType parameter shows the type of the ICMP messages and the MessageSubType parameter shows its subtype.

The MessageData parameter contains the message data.

The Checksum parameter is True or False depending on the ICMP checksum validation on the message.

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 (ICMP 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 (ICMP 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 (ICMP 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.

ICMP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (ICMP Component)

ICMP Errors

SSL Errors

TCP/IP Errors