Spider B4X (B4A / B4J) Reference Documentation

ChilkatSpider

Current Version: 11.6.0

Chilkat.Spider

Crawl a website domain, manage URL queues, filter links, cache pages, and inspect fetched HTML.

Chilkat.Spider crawls pages within a single initialized domain. It maintains internal lists of unspidered, spidered, failed, and outbound URLs; fetches one page at a time; extracts same-domain links for continued crawling; collects outbound links separately; respects robots.txt; supports wildcard include and avoid patterns; can use a dedicated cache directory; and exposes the last fetched HTML, title, meta description, keywords, redirect information, cache status, and last-modified date.

Domain-limited crawling

Initialize the spider with a domain and crawl only URLs that belong to that same domain.

URL queue management

Add starting URLs, crawl the next queued URL, skip selected URLs, and inspect unspidered, spidered, failed, and outbound URL lists.

Filtering rules

Add wildcard avoid patterns, must-match patterns, and outbound-link avoid patterns to control which URLs are crawled or collected.

Page metadata

Read the last fetched HTML, page title, meta description, meta keywords, final redirect URL, and last-modified timestamp.

Caching and redirects

Fetch pages from a Chilkat-managed cache, update the cache, detect when a page was redirected, and inspect whether the last page came from cache.

Network controls

Configure user-agent, proxy settings, connect/read timeouts, IPv6 preference, maximum URL length, maximum response size, and abort support.

Common pattern: Call Initialize with the target domain, add one or more starting URLs with AddUnspidered, optionally add filtering patterns, then repeatedly call CrawlNext. After each successful crawl, inspect LastUrl, LastHtml, page metadata, redirect state, and the URL-list counts to decide whether to continue, skip, recrawl, or process the page.
Scope note: Spider is intended for controlled, domain-oriented crawling and link discovery. Use Chilkat.Http or Chilkat.Rest when the task is a single HTTP request, API call, form post, or download rather than a crawl of discovered links.

Declare / Initialize / Dispose

Sub Process_Globals
    Private obj As ChilkatSpider
End Sub

' Call Initialize before first use -- typically in AppStart (B4J)
' or Activity_Create (B4A):
obj.Initialize                ' classes without events
obj.Initialize("evt")        ' classes with events: "evt" becomes the
                              ' prefix of event Subs such as evt_PercentDone
Initialize  /  Initialize (EventName As String)

Creates the underlying native Chilkat object. Classes that support events take an EventName argument: it becomes the prefix of the event Subs (<EventName>_AbortCheck, <EventName>_PercentDone, <EventName>_ProgressInfo); classes without events take no arguments. The native Chilkat library loads automatically on the first Initialize — from the APK on Android, or extracted from ChilkatB4J.jar on Windows/Linux/macOS.

IsInitialized As Boolean

True if Initialize has been called and the native object exists.

Dispose

Explicitly frees the underlying native object. Calling Dispose is optional — every ChilkatSpider is also freed automatically when garbage-collected — but is recommended for long-lived objects holding sockets, sessions, or large buffers. A disposed object can be re-Initialized.

Properties

AbortCurrent
' read/write
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.)

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AvoidHttps
' read/write
AvoidHttps As Boolean

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

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CacheDir
' read/write
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
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ChopAtQuery
' read/write
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).

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ConnectTimeout
' read/write
ConnectTimeout As Int

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

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DebugLogFilePath
' read/write
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
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Domain
' read-only
Domain As String

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

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FetchFromCache
' read/write
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
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FinalRedirectUrl
' read-only
FinalRedirectUrl As String
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.

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HeartbeatMs
' read/write
HeartbeatMs As Int

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
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LastErrorHtml
' read-only
LastErrorHtml As String

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.

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LastErrorText
' read-only
LastErrorText As String

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.

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LastErrorXml
' read-only
LastErrorXml As String

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.

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LastFromCache
' read-only
LastFromCache As Boolean

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

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LastHtml
' read-only
LastHtml As String

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

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LastHtmlDescription
' read-only
LastHtmlDescription As String

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

More Information and Examples
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LastHtmlKeywords
' read-only
LastHtmlKeywords As String

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

More Information and Examples
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LastHtmlTitle
' read-only
LastHtmlTitle As String

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

More Information and Examples
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LastMethodSuccess
' read/write
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. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.

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LastModDateStr
' read-only
LastModDateStr As String

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

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LastUrl
' read-only
LastUrl As String

The URL of the last page spidered.

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MaxResponseSize
' read/write
MaxResponseSize As Int

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
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MaxUrlLen
' read/write
MaxUrlLen As Int

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
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NumAvoidPatterns
' read-only
NumAvoidPatterns As Int

The number of avoid patterns previously set by calling AddAvoidPattern.

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NumFailed
' read-only
NumFailed As Int

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

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NumOutboundLinks
' read-only
NumOutboundLinks As Int

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

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NumSpidered
' read-only
NumSpidered As Int

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

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NumUnspidered
' read-only
NumUnspidered As Int

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

More Information and Examples
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PreferIpv6
' read/write
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.

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ProxyDomain
' read/write
ProxyDomain As String

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

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ProxyLogin
' read/write
ProxyLogin As String

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

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ProxyPassword
' read/write
ProxyPassword As String

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

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ProxyPort
' read/write
ProxyPort As Int

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

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ReadTimeout
' read/write
ReadTimeout As Int

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

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UpdateCache
' read/write
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
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UserAgent
' read/write
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.

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VerboseLogging
' read/write
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.

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Version
' read-only
Version As String

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

More Information and Examples
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WasRedirected
' read-only
WasRedirected As Boolean
Introduced in version 9.5.0.85

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

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WindDownCount
' read/write
WindDownCount As Int

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.

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Methods

AddAvoidOutboundLinkPattern
AddAvoidOutboundLinkPattern (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
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AddAvoidPattern
AddAvoidPattern (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
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AddMustMatchPattern
AddMustMatchPattern (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
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AddUnspidered
AddUnspidered (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
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CanonicalizeUrl
CanonicalizeUrl (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 Null on failure

More Information and Examples
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ClearFailedUrls
ClearFailedUrls

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

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ClearOutboundLinks
ClearOutboundLinks

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

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ClearSpideredUrls
ClearSpideredUrls

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

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CrawlNext
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
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FetchRobotsText
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 Null on failure

More Information and Examples
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GetAvoidPattern
GetAvoidPattern (index As Int) As String

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

Returns Null on failure

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GetBaseDomain
GetBaseDomain (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 Null on failure

More Information and Examples
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GetFailedUrl
GetFailedUrl (index As Int) As String

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

Returns Null on failure

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GetOutboundLink
GetOutboundLink (index As Int) As String

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

Returns Null on failure

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GetSpideredUrl
GetSpideredUrl (index As Int) As String

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

Returns Null on failure

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GetUnspideredUrl
GetUnspideredUrl (index As Int) As String

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

Returns Null on failure

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GetUrlDomain
GetUrlDomain (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 Null on failure

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Initialize
' In B4X this method is named InitializeSpider (Initialize is reserved by the B4X object lifecycle).
InitializeSpider (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
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RecrawlLast
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.

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SkipUnspidered
SkipUnspidered (index As Int)

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

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SleepMs
SleepMs (numMilliseconds As Int)

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

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Events

All Chilkat methods are synchronous: the call returns when the work is done. During a call, ChilkatSpider raises three events so your application can show progress and offer a way out. The event-name prefix is the string passed to Initialize:

spdr.Initialize("evt")     ' event Subs are named evt_AbortCheck, evt_PercentDone, evt_ProgressInfo
spdr.HeartbeatMs = 250     ' raise evt_AbortCheck 4 times per second during Chilkat calls

AbortCheck fires at regular intervals controlled by the HeartbeatMs property (0, the default, disables it); PercentDone fires when an operation's completion percentage is known; ProgressInfo delivers named progress values. Returning True from an AbortCheck or PercentDone Sub aborts the running method. Implement only the Subs you need — events are skipped entirely when no matching Sub exists.

If a Chilkat call runs on a separate thread (e.g. via the Threading library), its events are automatically queued to the main thread. Events raised that way cannot abort by return value; set the object's AbortCurrent property to True instead.

AbortCheck
' evt = the EventName passed to Initialize
' Return True to abort the Chilkat method in progress.
Sub evt_AbortCheck As Boolean

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

Example (object initialized with spdr.Initialize("evt")):

spdr.HeartbeatMs = 250   ' fire evt_AbortCheck 4 times per second

Sub evt_AbortCheck As Boolean
    ' Called every HeartbeatMs milliseconds while a Chilkat method is running.
    Return False   ' Return True to abort the method in progress
End Sub
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PercentDone
' evt = the EventName passed to Initialize
' Return True to abort the Chilkat method in progress.
Sub evt_PercentDone (PctDone As Int) As Boolean

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

Example (object initialized with spdr.Initialize("evt")):

Sub evt_PercentDone (PctDone As Int) As Boolean
    ' PctDone ranges from 1 to 100.
    Log("Percent done: " & PctDone)
    Return False   ' Return True to abort the method in progress
End Sub
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ProgressInfo
' evt = the EventName passed to Initialize
Sub evt_ProgressInfo (Name As String, Value As String)

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.

Note: Some Chilkat methods don't fire any ProgressInfo events.

More Information and Examples

Example (object initialized with spdr.Initialize("evt")):

Sub evt_ProgressInfo (Name As String, Value As String)
    Log(Name & ": " & Value)
End Sub
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