DNS Control

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The DNS control is used to query DNS for record information.

Syntax

DNS

Remarks

The DNS control queries a DNS server for records as specified in RFC 1035 and other relevant RFCs. The control property QueryType indicates the record to be queried. Calling Query will initiate the query.

Once the query is complete, a single Response event will fire and the record properties will be filled. StatusCode is the server's success or fail code, and Status is a standard string interpretation of the code.

The records are contained in the Records properties. The programming interface is designed to allow a full walk of the records in the DNS response, including provisions for handling new record types.

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

Property List

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

DNSPort Property (DNS Control)

This is the port to connect to on the DNS server.

Syntax

dnscontrol.DNSPort[=integer]

Default Value

53

Remarks

This property contains the port to connect to on the DNS server. A valid port number (a value between 1 and 65535) is required for the connection to take place. The property must be set before a connection is attempted and cannot be changed once a connection is established. Any attempt to change this property while connected will fail with an error.

This property is not available at design time.

Data Type

Integer

DNSServer Property (DNS Control)

This is the address of the DNS server.

Syntax

dnscontrol.DNSServer[=string]

Default Value

""

Remarks

This property contains the address of the DNS server. The control attempts to find the default DNS server for the machine where it is installed, and provide it in the DNSServer property. You may change it to any particular DNS server you want to query. While any internet host running a DNS service will suffice, it is preferable to use either the DNS server for your network or the DNS server for the domain that you are querying.

If the control cannot determine the default DNS server address, the property value will be an empty string.

Note: Automatic discovery of the default DNS server is not supported in the Java edition.

This property is not available at design time.

Data Type

String

Idle Property (DNS Control)

The current status of the control.

Syntax

dnscontrol.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.

Data Type

Boolean

LocalHost Property (DNS Control)

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

Syntax

dnscontrol.LocalHost[=string]

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 control initiate connections (or accept in the case of server controls) 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 control 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.

Data Type

String

Protocol Property (DNS Control)

This protocol is used for the DNS request.

Syntax

dnscontrol.Protocol[=integer]

Possible Values

ptUDP(0), 
ptTCP(1), 
ptTLS(2), 
ptHTTPS(3)

Default Value

0

Remarks

This property specifies the protocol used for the DNS request when Query is called. Possible values include the following:

Data Type

Integer

QueryType Property (DNS Control)

This is the type of record to query.

Syntax

dnscontrol.QueryType[=integer]

Possible Values

qtAddress(1), 
qtNS(2), 
qtMD(3), 
qtMF(4), 
qtCName(5), 
qtSOA(6), 
qtMailBox(7), 
qtMailGroup(8), 
qtMR(9), 
qtNULL(10), 
qtWKS(11), 
qtPointer(12), 
qtHostInfo(13), 
qtMailInfo(14), 
qtMX(15), 
qtText(16), 
qtRP(17), 
qtAFSDB(18), 
qtX25(19), 
qtISDN(20), 
qtRT(21), 
qtAAAA(28), 
qtSRV(33), 
qtNAPTR(35), 
qtCERT(37), 
qtRevLookup(100)

Default Value

1

Remarks

Before a query is attempted, this property must be set to the desired record type. The records are defined as follows:

This property is not available at design time.

Data Type

Integer

RecordCount Property (DNS Control)

The number of records in the Record arrays.

Syntax

dnscontrol.RecordCount

Default Value

0

Remarks

This property controls the size of the following arrays:

• RecordData
• RecordDomain
• RecordFieldCount
• RecordFieldIndex
• RecordFieldName
• RecordFieldValue
• RecordTTL
• RecordType
• RecordTypeName

The array indices start at 0 and end at RecordCount - 1.

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

Data Type

Integer

RecordDomain Property (DNS Control)

This property contains the domain name associated with the selected response record, at RecordIndex .

Syntax

dnscontrol.RecordDomain(RecordIndex)

Default Value

""

Remarks

This property contains the domain name associated with the selected response record, at RecordIndex.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

String

RecordFieldCount Property (DNS Control)

This property contains the number of properties in the current record.

Syntax

dnscontrol.RecordFieldCount(RecordIndex)

Default Value

0

Remarks

This property contains the number of properties in the current record.

After a successful query, the field values for each record will be provided in the Records properties.

To retrieve a particular field value for a record, first set RecordFieldIndex to a valid response field index and then query records collection for the value of that field.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

Integer

RecordFieldIndex Property (DNS Control)

This property contains the index of the selected property of the current record.

Syntax

dnscontrol.RecordFieldIndex(RecordIndex)[=integer]

Default Value

1

Remarks

This property contains the index of the selected property of the current record. RecordFieldIndex valid values are from 0 to (RecordFieldCount -1).

After a successful query, the field values for each record will be provided in the Records properties.

To retrieve a particular field value for a record, first set RecordFieldIndex to a valid response field index and then query records collection for the value of that field.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

This property is not available at design time.

Data Type

Integer

RecordFieldName Property (DNS Control)

This property contains the name of the property selected by FieldIndex .

Syntax

dnscontrol.RecordFieldName(RecordIndex)

Default Value

"0"

Remarks

This property contains the name of the field selected by RecordFieldIndex. Field names are different depending on the record type. For example, an MX record type will contain two properties: PREFERENCE and EXCHANGE, but an SOA record type contains seven properties.

Field names:

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

String

RecordFieldValue Property (DNS Control)

This property contains the value of the property selected by FieldIndex .

Syntax

dnscontrol.RecordFieldValue(RecordIndex)

Default Value

""

Remarks

This property contains the value of the field selected by RecordFieldIndex.

After a successful query, the field values for each record will be provided in the Records properties.

To retrieve a particular field value for a record, first set RecordFieldIndex to a valid response field index and then query records collection for the value of that field.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .RecordFieldValueB.

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

Data Type

Binary String

RecordData Property (DNS Control)

This property contains the full record data as received from the DNS server.

Syntax

dnscontrol.RecordData(RecordIndex)

Default Value

""

Remarks

This property contains the full record data as received from the DNS server.

After a successful query, the field values for each record will be provided in the Records properties.

To retrieve a particular field value for a record, first set RecordFieldIndex to a valid response field index and then query records collection for the value of that field.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

To read or write binary data to the property, a Variant (Byte Array) version is provided in .RecordDataB.

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

Data Type

Binary String

RecordType Property (DNS Control)

This property contains the record type.

Syntax

dnscontrol.RecordType(RecordIndex)

Possible Values

rtAddress(1), 
rtNS(2), 
rtMD(3), 
rtMF(4), 
rtCName(5), 
rtSOA(6), 
rtMailBox(7), 
rtMailGroup(8), 
rtMR(9), 
rtNULL(10), 
rtWKS(11), 
rtPointer(12), 
rtHostInfo(13), 
rtMailInfo(14), 
rtMX(15), 
rtText(16), 
rtRP(17), 
rtAFSDB(18), 
rtX25(19), 
rtISDN(20), 
rtRT(21), 
rtAAAA(28), 
rtSRV(33), 
rtNAPTR(35)

Default Value

1

Remarks

This property contains the record type.

Record types correspond to QueryType and are defined as follows:

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

Integer

RecordTypeName Property (DNS Control)

This property contains the string representation of the current record type defined by RecordType .

Syntax

dnscontrol.RecordTypeName(RecordIndex)

Default Value

""

Remarks

This property contains the string representation of the current record type defined by RecordType.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

String

RecordTTL Property (DNS Control)

This property contains the record Time to Live (TTL) value.

Syntax

dnscontrol.RecordTTL(RecordIndex)

Default Value

0

Remarks

This property contains the record Time to Live (TTL) value. The TTL specifies the time interval in seconds that the record is valid, or the time interval that the record can be cached before the DNS server should be queried again.

The RecordIndex parameter specifies the index of the item in the array. The size of the array is controlled by the RecordCount property.

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

Data Type

Integer

RecordSource Property (DNS Control)

The source of records provided in the Records properties.

Syntax

dnscontrol.RecordSource[=integer]

Possible Values

rsAnswerSection(0), 
rsNameServerSection(1), 
rsAdditionalRecordsSection(2)

Default Value

0

Remarks

This property contains the source of records provided in the Records properties and can have one of the following values:

This property is not available at design time.

Data Type

Integer

Recursive Property (DNS Control)

This determines whether to ask the DNSServer to recursively query other servers.

Syntax

dnscontrol.Recursive[=boolean]

Default Value

True

Remarks

If this property is True, the component will tell the DNS server to perform the query recursively. This means that if the DNS server does not have information about the domain being queried, it will send the request to another DNS server.

This property is not available at design time.

Data Type

Boolean

RequestId Property (DNS Control)

This is the Id of the current DNS request.

Syntax

dnscontrol.RequestId[=integer]

Default Value

1

Remarks

This property is the identifier of the request that generated the current response values. Each time the control makes a DNS query, it generates a unique request identifier to track the response.

If a custom value is needed for RequestId, the property must be set before sending a request. The control increments RequestId automatically after sending each request.

Note: The control fails with an error when a value that is not between 1 and 32,767 is specified.

This property is not available at design time.

Data Type

Integer

Status Property (DNS Control)

This is a standard string interpretation of StatusCode .

Syntax

dnscontrol.Status

Default Value

""

Remarks

This property contains a standard string interpretation of StatusCode. For a list of valid error codes and their descriptions, please see the Error Codes section.

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

Data Type

String

StatusCode Property (DNS Control)

This contains the success or error code for the DNS query.

Syntax

dnscontrol.StatusCode

Default Value

0

Remarks

This property contains the success or error code for the DNS query. For a list of valid error codes and their descriptions, please see the Error Codes section.

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

Data Type

Integer

Timeout Property (DNS Control)

This property includes the timeout for the control.

Syntax

dnscontrol.Timeout[=integer]

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 control will wait for the operation to complete before returning control. The control will handle any potential WOULDBLOCK errors internally and automatically retry the operation for a maximum of Timeout seconds.

The control 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 control fails with an error.

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.

Data Type

Integer

Config Method (DNS Control)

Sets or retrieves a configuration setting.

Syntax

dnscontrol.Config ConfigurationString

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the control, 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.

DoEvents Method (DNS Control)

This method processes events from the internal message queue.

Syntax

dnscontrol.DoEvents 

Remarks

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

GetFieldValue Method (DNS Control)

This gets the value of the field indicated from a record.

Syntax

dnscontrol.GetFieldValue RecordIndex, FieldName

Remarks

This method will get the value of the DNS record field specified by FieldName from the DNS record at RecordIndex. If no such field exists for that record type, the component fails with an error.

Interrupt Method (DNS Control)

This method interrupts the current method.

Syntax

dnscontrol.Interrupt 

Remarks

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

Query Method (DNS Control)

This method queries a domain.

Syntax

dnscontrol.Query Domain

Remarks

This method will query the host Domain for any records of the type in QueryType. After the query, RequestId is the identifier corresponding to the request. Once the query is complete, a single Response event will fire. The following properties will contain the results:

Reset Method (DNS Control)

This method will reset the control.

Syntax

dnscontrol.Reset 

Remarks

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

Error Event (DNS Control)

Fired when information is available about errors during data delivery.

Syntax

Sub dnscontrol_Error(ErrorCode As Integer, Description As String)

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the control fails with an error.

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.

Log Event (DNS Control)

This event fires once for each log message.

Syntax

Sub dnscontrol_Log(LogLevel As Integer, Message As String, LogType As String)

Remarks

This event fires once for each log message generated by the control. The verbosity is controlled by the LogLevel setting.

LogLevel indicates the level of message. Possible values are as follows:

The value 1 (Info) logs basic information, including the URL, HTTP version, and status details.

The value 2 (Verbose) logs additional information about the request and response.

The value 3 (Debug) logs the headers and body for both the request and response, as well as additional debug information (if any).

Message is the log entry.

LogType identifies the type of log entry. Possible values are as follows:

• "Info"
• "RequestHeaders"
• "ResponseHeaders"
• "RequestBody"
• "ResponseBody"
• "ProxyRequest"
• "ProxyResponse"
• "FirewallRequest"
• "FirewallResponse"

Response Event (DNS Control)

This event fires after a DNS query.

Syntax

Sub dnscontrol_Response(RequestId As Integer, Domain As String, StatusCode As Integer, Description As String, Authoritative As Boolean)

Remarks

The Response event will fire after a call to Query. The RequestId parameter contains the request Id associated with the original query. Domain is the domain of the query. The Authoritative parameter is true if the response is from an authoritative name server. If there is an error returned by the server, StatusCode and Description provide them.

Once the query is complete, a single Response event will fire. The following properties will contain the results:

SSLServerAuthentication Event (DNS Control)

This event fires when connecting to the server.

Syntax

Sub dnscontrol_SSLServerAuthentication(RemoteAddress As String, RemotePort As Integer, CertEncoded As String, CertSubject As String, CertIssuer As String, Status As String, Accept As Boolean)

Remarks

This event allows the client to decide whether or not to continue with the connection process. The Accept parameter recommends whether to continue or close the connection. This is just a suggestion: application software must use its own logic to determine whether or not to continue.

When Accept is False, Status shows why the verification failed (otherwise, Status contains the string "OK"). If the client decides to continue, you can override and accept the certificate by setting the Accept parameter to True.

RemoteAddress is the IP address of the server.

RemotePort is the source port of the server.

CertEncoded is the Base64-encoded certificate presented by the server.

CertSubject is the subject of the certificate presented by the server.

CertIssuer is the subject of the issuer of the certificate presented by the server.

Status is the status of the certificate.

Accept defines whether the certificate is accepted.

SSLStatus Event (DNS Control)

This shows the progress of the secure connection.

Syntax

Sub dnscontrol_SSLStatus(RemoteAddress As String, RemotePort As Integer, Message As String)

Remarks

The event is fired for informational and logging purposes only. It is used to track the progress of the connection.

RemoteAddress is the IP address of the remote machine.

RemotePort is the port of the remote machine.

Message is the log message.

Config Settings (DNS Control)

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

DNS Config Settings

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (DNS Control)

DNS Errors

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

UDP Errors

SSL Errors

TCP/IP Errors