Spider VB.NET Reference Documentation

Spider

Current Version: 11.1.0

Chilkat Spider web crawler object.

Object Creation

Dim obj As New Chilkat.Spider()

Properties

AbortCurrent
AbortCurrent As Boolean
Introduced in version 9.5.0.58

When set to True, causes the currently running method to abort. Methods that always finish quickly (i.e.have no length file operations or network communications) are not affected. If no method is running, then this property is automatically reset to False when the next method is called. When the abort occurs, this property is reset to False. Both synchronous and asynchronous method calls can be aborted. (A synchronous method call could be aborted by setting this property from a separate thread.)

top
AvoidHttps
AvoidHttps As Boolean

If set the 1 (true) the spider will avoid all HTTPS URLs. The default is 0 (false).

top
CacheDir
CacheDir As String

Specifies a cache directory to use for spidering. If either of the FetchFromCache or UpdateCache properties are true, this is the location of the cache to be used. Note: the Internet Explorer, Netscape, and FireFox caches are completely separate from the Chilkat Spider cache directory. You should specify a new and empty directory.

More Information and Examples
top
ChopAtQuery
ChopAtQuery As Boolean

If equal to 1 (true), then the query portion of all URLs are automatically removed when adding to the unspidered list. The default value is 0 (false).

top
ConnectTimeout
ConnectTimeout As Integer

The maximum number of seconds to wait while connecting to an HTTP server.

top
DebugLogFilePath
DebugLogFilePath As String

If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.

Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.

Possible causes of hangs include:

  • A timeout property set to 0, indicating an infinite timeout.
  • A hang occurring within an event callback in the application code.
  • An internal bug in the Chilkat code causing the hang.

More Information and Examples
top
Domain
Domain As String (ReadOnly)

The domain name that is being spidered. This is the domain previously set in the Initialize method.

top
FetchFromCache
FetchFromCache As Boolean

If equal to 1 (true) then pages are fetched from cache when possible. If 0, the cache is ignored. The default value is 1. Regardless, if no CacheDir is set then the cache is not used.

More Information and Examples
top
FinalRedirectUrl
FinalRedirectUrl As String (ReadOnly)
Introduced in version 9.5.0.85

If the last URL crawled was redirected (as indicated by the WasRedirected property), this property will contain the final redirect URL.

top
HeartbeatMs
HeartbeatMs As Integer

The interval in milliseconds between each AbortCheck event callback, which enables an application to abort certain method calls before they complete. By default, HeartbeatMs is set to 0, meaning no AbortCheck event callbacks will trigger.

More Information and Examples
top
LastErrorHtml
LastErrorHtml As String (ReadOnly)

Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

top
LastErrorText
LastErrorText As String (ReadOnly)

Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

top
LastErrorXml
LastErrorXml As String (ReadOnly)

Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

top
LastFromCache
LastFromCache As Boolean (ReadOnly)

Equal to 1 if the last page spidered was fetched from the cache. Otherwise equal to 0.

top
LastHtml
LastHtml As String (ReadOnly)

The HTML text of the last paged fetched by the spider.

top
LastHtmlDescription
LastHtmlDescription As String (ReadOnly)

The HTML META description from the last page fetched by the spider.

More Information and Examples
top
LastHtmlKeywords
LastHtmlKeywords As String (ReadOnly)

The HTML META keywords from the last page fetched by the spider.

More Information and Examples
top
LastHtmlTitle
LastHtmlTitle As String (ReadOnly)

The HTML title from the last page fetched by the spider.

More Information and Examples
top
LastMethodSuccess
LastMethodSuccess As Boolean

Indicates the success or failure of the most recent method call: True means success, False means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages.

top
LastModDateStr
LastModDateStr As String (ReadOnly)

The last modification date/time (RFC822 format) from the last page fetched by the spider.

top
LastUrl
LastUrl As String (ReadOnly)

The URL of the last page spidered.

top
MaxResponseSize
MaxResponseSize As Integer

The maximum HTTP response size allowed. The spider will automatically fail any pages larger than this size. The default value is 250,000 bytes.

More Information and Examples
top
MaxUrlLen
MaxUrlLen As Integer

The maximum URL length allowed. URLs longer than this are not added to the unspidered list. The default value is 200.

More Information and Examples
top
NumAvoidPatterns
NumAvoidPatterns As Integer (ReadOnly)

The number of avoid patterns previously set by calling AddAvoidPattern.

top
NumFailed
NumFailed As Integer (ReadOnly)

The number of URLs in the object's failed URL list.

top
NumOutboundLinks
NumOutboundLinks As Integer (ReadOnly)

The number of URLs in the object's outbound links URL list.

top
NumSpidered
NumSpidered As Integer (ReadOnly)

The number of URLs in the object's already-spidered URL list.

top
NumUnspidered
NumUnspidered As Integer (ReadOnly)

The number of URLs in the object's unspidered URL list.

More Information and Examples
top
PreferIpv6
PreferIpv6 As Boolean

If True, then use IPv6 over IPv4 when both are supported for a particular domain. The default value of this property is False, which will choose IPv4 over IPv6.

top
ProxyDomain
ProxyDomain As String

The domain name of a proxy host if an HTTP proxy is used.

top
ProxyLogin
ProxyLogin As String

If an HTTP proxy is used and it requires authentication, this property specifies the HTTP proxy login.

top
ProxyPassword
ProxyPassword As String

If an HTTP proxy is used and it requires authentication, this property specifies the HTTP proxy password.

top
ProxyPort
ProxyPort As Integer

The port number of a proxy server if an HTTP proxy is used.

top
ReadTimeout
ReadTimeout As Integer

The maximum number of seconds to wait when reading from an HTTP server.

top
UpdateCache
UpdateCache As Boolean

If equal to 1 (true) then pages saved to the cache. If 0, the cache is ignored. The default value is 1. Regardless, if no CacheDir is set then the cache is not used.

More Information and Examples
top
UserAgent
UserAgent As String

The value of the HTTP user-agent header field to be sent with HTTP requests. This can be set to any desired value, but be aware that some websites may reject requests from unknown user agents.

top
VerboseLogging
VerboseLogging As Boolean

If set to True, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is False. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.

top
Version
Version As String (ReadOnly)

Version of the component/library, such as "10.1.0"

More Information and Examples
top
WasRedirected
WasRedirected As Boolean (ReadOnly)
Introduced in version 9.5.0.85

Indicates whether the last URL crawled was redirected. (True = yes, False = no)

top
WindDownCount
WindDownCount As Integer

The wind-down phase begins when this number of URLs has been spidered. When in the wind-down phase, no new URLs are added to the unspidered list. The default value is 0 which means that there is NO wind-down phase.

top

Methods

AddAvoidOutboundLinkPattern
Sub AddAvoidOutboundLinkPattern(ByVal pattern As String)

Adds a wildcarded pattern to prevent collecting matching outbound link URLs. For example, if *google* is added, then any outbound links containing the word google will be ignored. The * character matches zero or more of any character.

More Information and Examples
top
AddAvoidPattern
Sub AddAvoidPattern(ByVal pattern As String)

Adds a wildcarded pattern to prevent spidering matching URLs. For example, if *register* is added, then any url containing the word register is not spidered. The * character matches zero or more of any character.

More Information and Examples
top
AddMustMatchPattern
Sub AddMustMatchPattern(ByVal pattern As String)

Adds a wildcarded pattern to limit spidering to only URLs that match the pattern. For example, if */products/* is added, then only URLs containing /products/ are spidered. This is helpful for only spidering a portion of a website. The * character matches zero or more of any character.

More Information and Examples
top
AddUnspidered
Sub AddUnspidered(ByVal url As String)

To begin spidering you must call this method one or more times to provide starting points. It adds a single URL to the object's internal queue of URLs to be spidered.

More Information and Examples
top
CanonicalizeUrl
Function CanonicalizeUrl(ByVal url As String) As String

Canonicalizes a URL by doing the following:

  • Drops username/password if present.
  • Drops fragment if present.
  • Converts domain to lowercase.
  • Removes port 80 or 443
  • Remove default.asp, index.html, index.htm, default.html, index.htm, default.htm, index.php, index.asp, default.php, .cfm, .aspx, ,php3, .pl, .cgi, .txt, .shtml, .phtml
  • Remove www. from the domain if present.

Returns Nothing on failure

More Information and Examples
top
ClearFailedUrls
Sub ClearFailedUrls()

Clears the object's internal list of URLs that could not be downloaded.

top
ClearOutboundLinks
Sub ClearOutboundLinks()

Clears the object's internal list of outbound URLs that will automatically accumulate while spidering.

top
ClearSpideredUrls
Sub ClearSpideredUrls()

Clears the object's internal list of already-spidered URLs that will automatically accumulate while spidering.

top
CrawlNext
Function CrawlNext() As Boolean

Crawls the next URL in the internal list of unspidered URLs. The URL is moved from the unspidered list to the spidered list. Any new links within the same domain and not yet spidered are added to the unspidered list. (providing that they do not match avoid patterns, etc.) Any new outbound links are added to the outbound URL list. If successful, the HTML of the downloaded page is available in the LastHtml property. If there are no more URLs left unspidered, the method returns False. Information about the URL crawled is available in the properties LastUrl, LastFromCache, and LastModDate.

More Information and Examples
top
CrawlNextAsync (1)
Function CrawlNextAsync() As Task

Creates an asynchronous task to call the CrawlNext method with the arguments provided.

Note: Async method event callbacks happen in the background thread. Accessing and updating UI elements existing in the main thread may require special considerations.

Returns Nothing on failure

top
FetchRobotsText
Function FetchRobotsText() As String

Returns the contents of the robots.txt file from the domain being crawled. This spider object will not crawl URLs excluded by robots.txt. If you believe the spider is not behaving correctly, please notify us at support@chilkatsoft.com and provide information detailing a case that allows us to reproduce the problem.

Returns Nothing on failure

More Information and Examples
top
FetchRobotsTextAsync (1)
Function FetchRobotsTextAsync() As Task

Creates an asynchronous task to call the FetchRobotsText method with the arguments provided.

Note: Async method event callbacks happen in the background thread. Accessing and updating UI elements existing in the main thread may require special considerations.

Returns Nothing on failure

top
GetAvoidPattern
Function GetAvoidPattern(ByVal index As Integer) As String

Returns the Nth avoid pattern previously added by calling AddAvoidPattern. Indexing begins at 0.

Returns Nothing on failure

top
GetBaseDomain
Function GetBaseDomain(ByVal domain As String) As String

Returns the second-level + top-level domain of the domain. For example, if domain is xyz.example.com, this returns example.com. For some domains, such as xyz.example.co.uk, the top 3 levels are returned, such as example.co.uk.

Returns Nothing on failure

More Information and Examples
top
GetFailedUrl
Function GetFailedUrl(ByVal index As Integer) As String

Returns the Nth URL in the failed URL list. Indexing begins at 0.

Returns Nothing on failure

top
GetOutboundLink
Function GetOutboundLink(ByVal index As Integer) As String

Returns the Nth URL in the outbound link URL list. Indexing begins at 0.

Returns Nothing on failure

top
GetSpideredUrl
Function GetSpideredUrl(ByVal index As Integer) As String

Returns the Nth URL in the already-spidered URL list. Indexing begins at 0.

Returns Nothing on failure

top
GetUnspideredUrl
Function GetUnspideredUrl(ByVal index As Integer) As String

Returns the Nth URL in the unspidered URL list. Indexing begins at 0.

Returns Nothing on failure

top
GetUrlDomain
Function GetUrlDomain(ByVal url As String) As String

Returns the domain name part of a URL. For example, if the URL is https://www.chilkatsoft.com/test.asp, then www.chilkatsoft.com is returned.

Returns Nothing on failure

top
Initialize
Sub Initialize(ByVal domain As String)

Initializes the object to begin spidering a domain. Calling Initialize clears any patterns added via the AddAvoidOutboundLinkPattern, AddAvoidPattern, and AddMustMatchPattern methods. The domain name passed to this method is what is returned by the Domain property. The spider only crawls URLs within the same domain.

More Information and Examples
top
LoadTaskCaller
Function LoadTaskCaller(ByVal task As Task) As Boolean
Introduced in version 9.5.0.80

Loads the caller of the task's async method.

Returns True for success, False for failure.

top
RecrawlLast
Function RecrawlLast() As Boolean

Re-crawls the last URL spidered. This helpful when cookies set in a previous page load cause the page to be loaded differently the next time.

top
RecrawlLastAsync (1)
Function RecrawlLastAsync() As Task

Creates an asynchronous task to call the RecrawlLast method with the arguments provided.

Note: Async method event callbacks happen in the background thread. Accessing and updating UI elements existing in the main thread may require special considerations.

Returns Nothing on failure

top
SkipUnspidered
Sub SkipUnspidered(ByVal index As Integer)

Moves a URL from the unspidered list to the spidered list. This allows an application to skip a specific URL.

top
SleepMs
Sub SleepMs(ByVal numMilliseconds As Integer)

Suspends the execution of the current thread until the time-out interval elapses.

top

Events

AbortCheck
Event OnAbortCheck

Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the HeartbeatMs property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.

More Information and Examples

Args are passed using Chilkat.AbortCheckEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_OnAbortCheck(sender As Object, args As Chilkat.AbortCheckEventArgs) Handles spider.OnAbortCheck

    ...

End Sub
top
PercentDone
Event OnPercentDone

This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The pctDone argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have pctDone equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).

The PercentDone callback also acts as an AbortCheck event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.

To abort the operation, set the abort output argument to True. This will cause the method to terminate and return a failure status or corresponding failure value.

More Information and Examples

Args are passed using Chilkat.PercentDoneEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_OnPercentDone(sender As Object, args As Chilkat.PercentDoneEventArgs) Handles spider.OnPercentDone

    ...

End Sub
top
ProgressInfo
Event OnProgressInfo

This event callback provides tag name/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.

More Information and Examples

Args are passed using Chilkat.ProgressInfoEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_OnProgressInfo(sender As Object, args As Chilkat.ProgressInfoEventArgs) Handles spider.OnProgressInfo

    ...

End Sub
top
TaskCompleted
Event OnTaskCompleted

Called from the background thread when an asynchronous task completes.

More Information and Examples

Args are passed using Chilkat.TaskCompletedEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_OnTaskCompleted(sender As Object, args As Chilkat.TaskCompletedEventArgs) Handles spider.OnTaskCompleted

    ...

End Sub
top