Spider VB.NET WinRT Reference Documentation

Spider

Chilkat Spider web crawler component.

Object Creation

Dim obj As New Chilkat.Spider()

Properties

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.)

AvoidHttps As Boolean

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

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.

Caching Web Pages to the Filesystem

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).

ConnectTimeout As Integer

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

DebugLogFilePath As String

If set to a file path, causes each Chilkat method or property call to automatically append it's LastErrorText to the specified log file. The information is appended such that if a hang or crash occurs, it is possible to see the context in which the problem occurred, as well as a history of all Chilkat calls up to the point of the problem. The VerboseLogging property can be set to provide more detailed information.

This property is typically used for debugging the rare cases where a Chilkat method call hangs or generates an exception that halts program execution (i.e. crashes). A hang or crash should generally never happen. The typical causes of a hang are:

  1. a timeout related property was set to 0 to explicitly indicate that an infinite timeout is desired,
  2. the hang is actually a hang within an event callback (i.e. it is a hang within the application code), or
  3. there is an internal problem (bug) in the Chilkat code that causes the hang.

Domain As String (ReadOnly)

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

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.

Caching Web Pages to the Filesystem

HeartbeatMs As Integer

The number of milliseconds between each AbortCheck event callback. The AbortCheck callback allows an application to abort any method call prior to completion. If HeartbeatMs is 0 (the default), no AbortCheck event callbacks will fire.

LastErrorHtml As String (ReadOnly)

Provides information in HTML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

LastErrorText As String (ReadOnly)

Provides information in plain-text format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

LastErrorXml As String (ReadOnly)

Provides information in XML format about the last method/property called. If a method call returns a value indicating failure, or behaves unexpectedly, examine this property to get more information.

LastFromCache As Boolean (ReadOnly)

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

LastHtml As String (ReadOnly)

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

LastHtmlDescription As String (ReadOnly)

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

Extract HTML Title, Description, Keywords

LastHtmlKeywords As String (ReadOnly)

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

Extract HTML Title, Description, Keywords

LastHtmlTitle As String (ReadOnly)

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

Extract HTML Title, Description, Keywords

LastMethodSuccess As Boolean

Introduced in version 9.5.0.52

Indicate whether the last method call succeeded or failed. A value of True indicates success, a value of False indicates failure. This property is automatically set for method calls. It is not modified by property accesses. The property is automatically set to indicate success for the following types of method calls:

  • Any method that returns a string.
  • Any method returning a Chilkat object, binary bytes, or a date/time.
  • Any method returning a standard boolean status value where success = True and failure = False.
  • Any method returning an integer where failure is defined by a return value less than zero.

Note: Methods that do not fit the above requirements will always set this property equal to True. For example, a method that returns no value (such as a "void" in C++) will technically always succeed.

LastModDateStr As String (ReadOnly)

The last modification date/time from the last page fetched by the spider.

LastUrl As String (ReadOnly)

The URL of the last page spidered.

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.

Setting a Maximum Response Size

MaxUrlLen As Integer

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

Setting a Maximum URL Length

NumAvoidPatterns As Integer (ReadOnly)

The number of avoid patterns previously set by calling AddAvoidPattern.

NumFailed As Integer (ReadOnly)

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

NumOutboundLinks As Integer (ReadOnly)

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

NumSpidered As Integer (ReadOnly)

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

NumUnspidered As Integer (ReadOnly)

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

Getting Started Example

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.

ProxyDomain As String

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

ProxyLogin As String

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

ProxyPassword As String

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

ProxyPort As Integer

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

ReadTimeout As Integer

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

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.

Caching Web Pages to the Filesystem

UserAgent As String

The value of the HTTP user-agent header field to be sent with HTTP requests. The default value is "Chilkat/1.0.0 (+http://www.chilkatsoft.com/ChilkatHttpUA.asp)"

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.

Version As String (ReadOnly)

Version of the component/library, such as "9.4.1.42"

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.

Methods

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.

Avoiding Outbound Links Matching Patterns

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.

Avoid URLs Matching Any of a Set of Patterns

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.

Must-Match Patterns

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 component's internal queue of URLs to be spidered.

Crawling the Web

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

Canonicalize a URL

Sub ClearFailedUrls()

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

Sub ClearOutboundLinks()

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

Sub ClearSpideredUrls()

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

<Awaitable> Function CrawlNextAsync() As IAsyncOperation(Of 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.

Crawling the Web

Getting Started Example

<Awaitable> Function FetchRobotsTextAsync() As IAsyncOperation(Of String)

Returns the contents of the robots.txt file from the domain being crawled. This spider component 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

Fetch robots.txt for a Site

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

Function GetBaseDomain(ByVal domain As String) As String

To be documented soon.

Returns Nothing on failure

Convert a Domain Name into a "domain base"

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

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

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

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

Function GetUrlDomain(ByVal url As String) As String

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

Returns Nothing on failure

Sub Initialize(ByVal domain As String)

Initializes the component 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.

Crawling the Web

Getting Started Example

<Awaitable> Function RecrawlLastAsync() As IAsyncOperation(Of 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.

Function SaveLastError(ByVal path As String) As Boolean

Saves the last-error information (the contents of LastErrorXml) to an XML formatted file.

Returns True for success, False for failure.

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.

Sub SleepMs(ByVal numMilliseconds As Integer)

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

Events

Event AbortCheck

Provides the opportunity for a method call to be aborted. The AbortCheck event is fired periodically based on the value of the HeartbeatMs property. If HeartbeatMs is 0, then no AbortCheck events will fire. As an example, to fire 5 AbortCheck events per second, set the HeartbeatMs property equal to 200.

Args are passed using Chilkat.AbortCheckEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_AbortCheck(sender As Object, args As Chilkat.AbortCheckEventArgs) Handles spider.AbortCheck

    ...

End Sub

Event BinaryData

Binary data provided by certain methods.

Args are passed using Chilkat.BinaryDataEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_BinaryData(sender As Object, args As Chilkat.BinaryDataEventArgs) Handles spider.BinaryData

    ...

End Sub

Event PercentDone

Provides the percentage completed for any method that involves network communications or time-consuming processing (assuming it is a method where a percentage completion can be measured). This event is only fired when it is possible to know a percentage completion, and when it makes sense to express the operation as a percentage completed. The pctDone argument will have a value from 1 to 100. For operations (Chilkat method calls) that complete very quickly, the number of PercentDone callbacks will vary, but the final callback should have a value of 100. For long running operations, no more than one callback per percentage point will occur (for example: 1, 2, 3, ... 98, 99, 100).

The PercentDone callback counts as an AbortCheck event. For method calls that complete quickly such that PercentDone events fire, it may be that AbortCheck events don't fire because the opportunity to abort is already provided in the PercentDone callback. For time consuming operations, where the amount of time between PercentDone callbacks are long, AbortCheck callbacks may be used to allow for the operation to be aborted in a more responsive manner.

The abort output argument provides a means for aborting the operation. Setting it to True will cause the method to abort and return a failed status (or whatever return value indicates failure).

Args are passed using Chilkat.PercentDoneEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_PercentDone(sender As Object, args As Chilkat.PercentDoneEventArgs) Handles spider.PercentDone

    ...

End Sub

Event ProgressInfo

A general name/value event that provides information about what is happening during a method call. To find out what information is available, write code to handle this event and log the name/value pairs. Most are self-explanatory.

Args are passed using Chilkat.ProgressInfoEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_ProgressInfo(sender As Object, args As Chilkat.ProgressInfoEventArgs) Handles spider.ProgressInfo

    ...

End Sub

Event TaskCompleted

Called in the background thread when an asynchronous task completes.

Args are passed using Chilkat.TaskCompletedEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_TaskCompleted(sender As Object, args As Chilkat.TaskCompletedEventArgs) Handles spider.TaskCompleted

    ...

End Sub

Event TextData

Text data provided by certain methods.

Args are passed using Chilkat.TextDataEventArgs

Event callback implementation:

Dim WithEvents spider As Chilkat.Spider

Private Sub spider_TextData(sender As Object, args As Chilkat.TextDataEventArgs) Handles spider.TextData

    ...

End Sub