Ping Component

Properties   Methods   Events   Config Settings   Errors  

The PING component encapsulates Internet Control Message Protocol (ICMP) ECHO functionality, which is used to check whether there is a communications link between two computers.

Syntax

TipwPing

Remarks

When the PingHost method is called with the Host parameter, or if RemoteHost is assigned an IP address or domain name, the component sends an ICMP ECHO packet to the remote host. The ResponseTime and ResponseSource properties are updated with the time of the roundtrip to the remote host and the address of the host actually sending the response.

The component operates synchronously by default (i.e., waits for a response before returning control to the caller); however, the component may also operate asynchronously (i.e., returns control immediately) by setting Timeout to 0. Please refer to the Timeout property for more information.

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.

Active Property (Ping 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.

The PingHost method will automatically change the value of this property to True.

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

Idle Property (Ping Component)

The current status of the component.

Syntax

property Idle: Boolean read get_Idle;

Default Value

true

Remarks

This property will be False if the component is currently busy (communicating or waiting for an answer), and True at all other times.

This property is read-only.

LocalHost Property (Ping 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.

PacketSize Property (Ping Component)

This property includes the size of the packet to send as the ping request.

Syntax

property PacketSize: Integer read get_PacketSize write set_PacketSize;

Default Value

64

Remarks

This property allows you to control the size of the data packet sent in the PingHost method. The default packet size is 64 bytes, with a minimum of 8 bytes (4 bytes of the ICMP header plus the ECHO identifier). The maximum value is 65520.

RemoteHost Property (Ping 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).

RequestId Property (Ping Component)

This property includes a unique identifier for outgoing packets.

Syntax

property RequestId: Integer read get_RequestId;

Default Value

0

Remarks

This property contains a unique identifier for outgoing packets. This property is useful during asynchronous ping operations. The RequestId parameter of the Response event is used to match requests with responses.

The identifier of the outgoing ping packet is provided in this property after the PingHost method returns.

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

ResponseSource Property (Ping Component)

This property includes the source of the last PING response.

Syntax

property ResponseSource: String read get_ResponseSource;

Default Value

''

Remarks

This property contains the address of the host responding to the PING (ICMP ECHO) request. This may or may not be the host used in PingHost.

This property is read-only.

ResponseStatus Property (Ping Component)

This property includes the status of the last PING response.

Syntax

property ResponseStatus: String read get_ResponseStatus;

Default Value

''

Remarks

This property contains the status of the last response. After PingHost has returned, this property will be populated with the status of the response. For responses without error, the value will be OK. In the case of an error, the value will hold a description of the error, such as Network Unreachable or Host Unreachable.

This property is read-only.

ResponseTime Property (Ping Component)

This property includes the time elapsed between sending the original packet and the remote host reply.

Syntax

property ResponseTime: Integer read get_ResponseTime;

Default Value

0

Remarks

This property contains the time elapsed between sending the original packet and the remote host reply. The time value is expressed in milliseconds. The lowest resolution available depends on the resolution of the clock on the host system (normally between 10 ms and 20 ms).

This property is read-only.

Timeout Property (Ping Component)

This property includes the timeout for the component.

Syntax

property Timeout: Integer read get_Timeout write set_Timeout;

Default Value

60

Remarks

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

If Timeout is set to a positive value, data is sent in a blocking manner and the component will wait for the operation to complete before returning control. The component will handle any potential WOULDBLOCK errors internally and automatically retry the operation 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 60 seconds.

TimeToLive Property (Ping 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.

TypeOfService Property (Ping Component)

This property includes the type of ICMP message sent as a ping request.

Syntax

property TypeOfService: Integer read get_TypeOfService write set_TypeOfService;

Default Value

8

Remarks

This property contains the type of the ICMP message sent as a ping request. The default value is 8 (ECHO REQUEST).

This property is not available at design time.

Activate Method (Ping Component)

This method enables sending and receiving data.

Syntax

procedure Activate();

Remarks

This method enables sending and receiving of data.

Note: Calling the PingHost method will automatically activate the component.

Config Method (Ping 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 (Ping Component)

This method disables sending and receiving data.

Syntax

procedure Deactivate();

Remarks

This method disables sending and receiving data.

DoEvents Method (Ping 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.

Interrupt Method (Ping Component)

This method interrupts the current method.

Syntax

procedure Interrupt();

Remarks

If there is no method in progress, Interrupt simply returns, doing nothing.

PingHost Method (Ping Component)

This method pings a host.

Syntax

procedure PingHost(Host: String);

Remarks

This method will ping a host. A valid internet domain name or address must be specified in Host, or an error will be returned.

A PING request (ICMP ECHO) is sent to the Host.

Example. Ping a Host:

PingControl.PingHost("MyHostName") ResponseTime = PingControl.ResponseTime

Reset Method (Ping 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 (Ping 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.

WakeOnLAN Method (Ping Component)

This method sends a Wake-On-LAN packet.

Syntax

procedure WakeOnLAN(RemoteHost: String; MACAddress: String);

Remarks

When this method is called, a Wake-On-LAN packet is sent to RemoteHost (which may also be a broadcast address). This has the effect of powering on the machine (if such functionality is supported by the network card on the remote machine).

The physical address of the remote host must be supplied in the MACAddress parameter.

Error Event (Ping 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.

Response Event (Ping Component)

This event is fired when a response packet is received.

Syntax

type TResponseEvent = procedure (
  Sender: TObject;
  RequestId: Integer;
  const ResponseSource: String;
  const ResponseStatus: String;
  ResponseTime: Integer
) of Object;

property OnResponse: TResponseEvent read FOnResponse write FOnResponse;

Remarks

The RequestId parameter is used along with the RequestId property to match requests with responses.

ResponseStatus is set to OK for normal operation, or it contains an error string, such as Network unreachable or Host unreachable.

Config Settings (Ping 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.

Ping Config Settings

ICMP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (Ping Component)

Ping Errors

The component may also return one of the following error codes, which are inherited from other components.

ICMP Errors

SSL Errors

TCP/IP Errors