gocrawl

package module
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 Go to latest Published: Mar 26, 2013 License: BSD-3-Clause Imports: 15 Imported by: 0

README

gocrawl

gocrawl is a polite, slim and concurrent web crawler written in Go.

Features

  • Full control over the URLs to visit, inspect and query (using a pre-initialized goquery document)
  • Crawl delays applied per host
  • Obedience to robots.txt rules (using robotstxt.go go library)
  • Concurrent execution using goroutines
  • Configurable logging
  • Open, customizable design by providing hooks into the execution logic

Installation and dependencies

gocrawl depends on the following userland libraries:

Until Go1.1 is released, and because of the dependency on GoQuery that, in turns, depends on Go's experimental HTML package, some special steps must be followed to install GoQuery. Follow these steps before installing gocrawl.

Once this is done, gocrawl may be installed as usual:

go get github.com/PuerkitoBio/gocrawl

Changelog

  • v0.3,2 : Fix the high CPU usage when waiting for a crawl delay.
  • v0.3.1 : Export the HttpClient variable used by the default Fetch() implementation (see issue #9).
  • v0.3.0 : BEHAVIOR CHANGE filter done with normalized URL, fetch done with original, non-normalized URL (see issue #10).
  • v0.2.0 : BREAKING CHANGES rework extension/hooks.
  • v0.1.0 : Initial release.

Example

From example_test.go:

package gocrawl

import (
  "github.com/PuerkitoBio/goquery"
  "net/http"
  "net/url"
  "regexp"
  "time"
)

// Only enqueue the root and paths beginning with an "a"
var rxOk = regexp.MustCompile(`http://duckduckgo\.com(/a.*)?$`)

// Create the Extender implementation, based on the gocrawl-provided DefaultExtender,
// because we don't want/need to override all methods.
type ExampleExtender struct {
  DefaultExtender // Will use the default implementation of all but Visit() and Filter()
}

// Override Visit for our need.
func (this *ExampleExtender) Visit(res *http.Response, doc *goquery.Document) ([]*url.URL, bool) {
  // Use the goquery document or res.Body to manipulate the data
  // ...

  // Return nil and true - let gocrawl find the links
  return nil, true
}

// Override Filter for our need.
func (this *ExampleExtender) Filter(u *url.URL, src *url.URL, isVisited bool, origin EnqueueOrigin) (bool, int, HeadRequestMode) {
  // Priority (2nd return value) is ignored at the moment
  return !isVisited && rxOk.MatchString(u.String()), 0, HrmDefault
}

func ExampleCrawl() {
  // Set custom options
  opts := NewOptions(new(ExampleExtender))
  opts.CrawlDelay = 1 * time.Second
  opts.LogFlags = LogAll

  // Play nice with ddgo when running the test!
  opts.MaxVisits = 2

  // Create crawler and start at root of duckduckgo
  c := NewCrawlerWithOptions(opts)
  c.Run("https://duckduckgo.com/")

  // Remove "x" before Output: to activate the example (will run on go test)

  // xOutput: voluntarily fail to see log output
}

API

Gocrawl can be described as a minimalist web crawler (hence the "slim" tag, at <1000 sloc), providing the basic engine upon which to build a full-fledged indexing machine with caching, persistence and staleness detection logic, or to use as is for quick and easy crawling. Gocrawl itself does not attempt to detect staleness of a page, nor does it implement a caching mechanism. If an URL is enqueued to be processed, it will make a request to fetch it (provided it is allowed by robots.txt - hence the "polite" tag). And there is no prioritization among the URLs to process, it assumes that all enqueued URLs must be visited at some point, and that the order in which they are is unimportant - subject to change in the future, prioritization may get implemented.

However, it does provide plenty of hooks and customizations. Instead of trying to do everything and impose a way to do it, it offers ways to manipulate and adapt it to anyone's needs.

As usual, the complete godoc reference can be found here.

Design rationale

The major use-case behind gocrawl is to crawl some web pages while respecting the constraints of robots.txt policies and while applying a good web citizen crawl delay between each request to a given host. Hence the following design decisions:

  • Each host spawns its own worker (goroutine) : This makes sense since it must first read its robots.txt data, and only then proceed sequentially, one request at a time, with the specified delay between each fetch. There are no constraints inter-host, so each separate worker can crawl independently.
  • The visitor function is called on the worker goroutine : Again, this is ok because the crawl delay is likely bigger than the time required to parse the document, so this processing will usually not penalize the performance.
  • Edge cases with no crawl delay are supported, but not optimized : In the rare but possible event when a crawl with no delay is needed (e.g.: on your own servers, or with permission outside busy hours, etc.), gocrawl accepts a null (zero) delay, but doesn't provide optimizations. That is, there is no "special path" in the code where visitor functions are de-coupled from the worker, or where multiple workers can be launched concurrently on the same host. (In fact, if this case is your only use-case, I would recommend not to use a library at all - since there is little value in it -, and simply use Go's standard libs and fetch at will with as many goroutines as are necessary.)

Although it could probably be used to crawl a massive amount of web pages (after all, this is fetch, visit, enqueue, repeat ad nauseam!), most realistic (and um... tested!) use-cases should be based on a well-known, well-defined limited bucket of seeds. Distributed crawling is your friend, should you need to move past this reasonable use.

Crawler

The Crawler type controls the whole execution. It spawns worker goroutines and manages the URL queue. There are two helper constructors:

  • NewCrawler(Extender) : Creates a crawler with the specified Extender instance.
  • NewCrawlerWithOptions(Options) : Creates a crawler with a pre-initialized *Options instance.

The one and only public function is Run(seeds ...string) EndReason which take a variadic string argument, the base URLs used to start crawling. It ends when there are no more URLs waiting to be visited, or when the Options.MaxVisit number is reached.

Options

The Options type is detailed in the next section, and it offers a single constructor, NewOptions(Extender), which returns an initialized options object with defaults and the specified Extender implementation.

Hooks and customizations

The Options type provides the hooks and customizations offered by gocrawl. All but Extender are optional and have working defaults.

  • UserAgent : The user-agent string used to fetch the pages. Defaults to the Firefox 15 on Windows user-agent string.

  • RobotUserAgent : The robot's user-agent string used to fetch and query robots.txt for permission to crawl an URL. Defaults to Googlebot (gocrawl vM.m) where M.m is the major and minor version of gocrawl. See the robots exclusion protocol (full specification as interpreted by Google here) for details about the rule-matching based on the robot's user agent. It is good practice to include contact information in the user agent should the site owner need to contact you.

  • MaxVisits : The maximum number of pages visited before stopping the crawl. Probably more useful for development purposes. Note that the Crawler will send its stop signal once this number of visits is reached, but workers may be in the process of visiting other pages, so when the crawling stops, the number of pages visited will be at least MaxVisits, possibly more (worst case is MaxVisits + number of active workers). Defaults to zero, no maximum.

  • EnqueueChanBuffer : The size of the buffer for the Enqueue channel (the channel that allows the extender to arbitrarily enqueue new URLs in the crawler). Defaults to 100.

  • HostBufferFactor : The factor (multiplier) for the size of the workers map and the communication channel when SameHostOnly is set to false. When SameHostOnly is true, the Crawler knows exactly the required size (the number of different hosts based on the seed URLs), but when it is false, the size may grow exponentially. By default, a factor of 10 is used (size is set to 10 times the number of different hosts based on the seed URLs).

  • CrawlDelay : The time to wait between each request to the same host. The delay starts as soon as the response is received from the host. This is a time.Duration type, so it can be specified with 5 * time.Second for example (which is the default value, 5 seconds). If a crawl delay is specified in the robots.txt file, in the group matching the robot's user-agent, by default this delay is used instead. Crawl delay can be customized further by implementing the ComputeDelay extender function.

  • WorkerIdleTTL : The idle time-to-live allowed for a worker before it is cleared (its goroutine terminated). Defaults to 10 seconds. The crawl delay is not part of idle time, this is specifically the time when the worker is available, but there are no URLs to process.

  • SameHostOnly : Limit the URLs to enqueue only to those links targeting the same host, which is true by default.

  • HeadBeforeGet : Asks the crawler to issue a HEAD request (and a subsequent RequestGet() extender method call) before making the eventual GET request. This is set to false by default. See also the Filter() extender method.

  • URLNormalizationFlags : The flags to apply when normalizing the URL using the purell library. The URLs found by crawling a page are normalized before being submitted to the Filter extender function (to determine if they should be visited or not). Defaults to the most aggressive normalization allowed by purell, purell.FlagsAllGreedy.

  • LogFlags : The level of verbosity for logging. Defaults to errors only (LogError). Can be a set of flags (i.e. LogError | LogTrace).

  • Extender : The instance implementing the Extender interface. This implements the various callbacks offered by gocrawl. Must be specified when creating a Crawler (or when creating an Options to pass to NewCrawlerWithOptions constructor). A default extender is provided as a valid default implementation, DefaultExtender. It can be used by embedding it as an anonymous field to implement a custom extender when not all methods need customization (see the example above).

The Extender interface

This last option field, Extender, is crucial in using gocrawl, so here are the details for each callback function required by the Extender interface.

  • Start : Start(seeds []string) []string. Called when Run is called on the crawler, with the seeds passed to Run as argument. It returns a slice of strings that will be used as actual seeds, so that this callback can control which seeds are passed to the crawler.

  • End : End(reason EndReason). Called when the crawling ends, with an EndReason flag as argument. This same EndReason flag is also returned from the Crawler.Run() function.

  • Error : Error(err *CrawlError). Called when an error occurs. Errors do not stop the crawling execution. A CrawlError instance is passed as argument. This specialized error implementation includes - among other interesting fields - a Kind field that indicates the step where the error occurred.

  • Log : Log(logFlags LogFlags, msgLevel LogFlags, msg string). The logging function. By default, prints to the standard error (Stderr), and outputs only the messages with a level included in the LogFlags option. If a custom Log() method is implemented, it is up to you to validate if the message should be considered, based on the level of verbosity requested (i.e. if logFlags&msgLevel == msgLevel ...), since the method always gets called for all messages.

  • ComputeDelay : ComputeDelay(host string, di *DelayInfo, lastFetch *FetchInfo) time.Duration. Called by a worker before requesting a URL. Arguments are the host's name, the crawl delay information (delays from the Options struct, from the robots.txt, and the last used delay), and the last fetch information, so that it is possible to adapt to the current responsiveness of the host. It returns the delay to use.

  • Fetch : Fetch(u *url.URL, userAgent string, headRequest bool) (*http.Response, error). Called by a worker to request the URL. The DefaultExtender.Fetch() implementation uses the public HttpClient variable (a custom http.Client) to fetch the pages without following redirections, instead returning an error so that the worker can enqueue the redirect-to URL. This enforces the whitelisting by the Filter() of every URL fetched by the crawling process. If headRequest is true, a HEAD request is made instead of a GET. Note that as of gocrawl v0.3, Fetch is called with the non-normalized URL.

Internally, gocrawl sets its http.Client's `CheckRedirect()` function field to a custom implementation that follows redirections for robots.txt URLs only (since a redirect on robots.txt still means that the site owner wants us to use these rules for this host). The worker is aware of the `*gocrawl.EnqueueRedirectError` error, so if a non-robots.txt URL asks for a redirection, `CheckRedirect()` returns an instance of this error, and the worker recognizes this and enqueues the redirect-to URL, stopping the processing of the current URL. It is possible to provide a custom `Fetch()` implementation based on the same logic. Any `CheckRedirect()` implementation that returns a `*gocrawl.EnqueueRedirectError` error will behave this way - that is, the worker will detect this error and will enqueue the redirect-to URL. See the source files ext.go and worker.go for details.

The `HttpClient` variable being public, it is possible to customize it so that it uses another `CheckRedirect()` function, or a different `Transport` object, etc. This customization should be done prior to starting the crawler. It will then be used by the default `Fetch()` implementation, or it can also be used by a custom `Fetch()` if required. Note that this client is shared by all crawlers in your application. Should you need different http clients per crawler in the same application, a custom `Fetch()` using a private `http.Client` instance should be provided.

  • RequestGet : RequestGet(headRes *http.Response) bool. Indicates if the crawler should proceed with a GET request based on the HEAD request's response. This method is only called if a HEAD was requested (either via the global HeadBeforeGet option, or via the Filter() return value). The default implementation returns true if the HEAD response status code was 2xx.

  • RequestRobots : RequestRobots(u *url.URL, robotAgent string) (request bool, data []byte). Asks whether the robots.txt URL should be fetched. If false is returned as first value, the data value is considered to be the robots.txt cached content, and is used as such (if it is empty, it behaves as if there was no robots.txt). The DefaultExtender.RequestRobots implementation returns true, nil.

  • FetchedRobots : FetchedRobots(res *http.Response). Called when the robots.txt URL has been fetched from the host, so that it is possible to cache its content and feed it back to future RequestRobots() calls. By default, this is a no-op.

  • Filter : Filter(u *url.URL, from *url.URL, isVisited bool, origin EnqueueOrigin) (enqueue bool, priority int, headRequest HeadRequestMode). Called when deciding if a URL should be enqueued for visiting. It receives the target *url.URL link in normalized form, the source *url.URL link (where this URL was found, nil for the seeds or for manually enqueued URLs, via the enqueue channel - see below), a bool is visited flag, indicating if this URL has already been visited in this crawling execution, and an origin (which can be extended to create custom origins, starting at EoCustomStart instead of iota). It returns a bool flag ordering gocrawl to visit (true) or ignore (false) the URL, a priority value, ignored at the moment, and whether or not to request a HEAD before a GET (if HrmDefault is returned, the global HeadBeforeGet setting is used, while HrmRequest and HrmIgnore override the global setting). Even if the function returns true to enqueue the URL for visiting, the normalized form of the URL must still comply to these rules:

  1. It must be an absolute URL

  2. It must have a http/https scheme

  3. It must have the same host if the SameHostOnly flag is set

    The DefaultExtender.Filter implementation returns true if the URL has not been visited yet (the visited flag is based on the normalized version of the URLs), false otherwise. It returns 0 for the priority and HrmDefault for the head request.

  • Enqueued : Enqueued(u *url.URL, from *url.URL). Called when a URL has been enqueued by the crawler. An enqueued URL may still be disallowed by a robots.txt policy, so it may end up not being fetched.

  • Visit : Visit(res *http.Response, doc *goquery.Document) (harvested []*url.URL, findLinks bool). Called when visiting a URL. It receives a *http.Response response object, along with a ready-to-use *goquery.Document object (or nil if the response body could not be parsed). It returns a slice of *url.URL links to process, and a bool flag indicating if gocrawl should find the links himself. When this flag is true, the slice of URLs is ignored and gocrawl searches the goquery document for links to enqueue. When false, the returned slice of URLs is enqueued, if any. The DefaultExtender.Visit implementation returns nil, true so that links from a visited page are found and processed.

  • Visited : Visited(u *url.URL, harvested []*url.URL). Called after a page has been visited. The URLs found during the visit (either by the Visit function or by gocrawl) are passed as argument.

  • Disallowed : Disallowed(u *url.URL). Called when an enqueued URL gets denied acces by a robots.txt policy.

Finally, by convention, if a field named EnqueueChan with the very specific type of chan<- *CrawlerCommand exists and is accessible on the Extender instance, this field will get set to the enqueue channel, which accepts a pointer to a CrawlerCommand structure, specifying a URL and an origin. This URL will then be processed by the crawler as if it had been harvested from a visit. It will trigger a call to Filter() and, if allowed, will get fetched and visited.

The DefaultExtender structure has a valid EnqueueChan field, so if it is embedded as an anonymous field in a custom Extender structure, this structure automatically gets the EnqueueChan functionality.

This channel can be useful to arbitrarily enqueue URLs that would otherwise not be processed by the crawling process. For example, if an URL raises a server error (status code 5xx), it could be re-enqueued in the Error() extender function, so that another fetch is attempted.

Thanks

  • Richard Penman
  • Dmitry Bondarenko
  • Markus Sonderegger

License

The BSD 3-Clause license.

Documentation

Overview

gocrawl is a polite, slim and concurrent web crawler written in Go.

Index

Constants

View Source 
const (
	DefaultUserAgent          string                    = `Mozilla/5.0 (Windows NT 6.1; rv:15.0) Gecko/20120716 Firefox/15.0a2`
	DefaultRobotUserAgent     string                    = `Googlebot (gocrawl v0.3)`
	DefaultEnqueueChanBuffer  int                       = 100
	DefaultHostBufferFactor   int                       = 10
	DefaultCrawlDelay         time.Duration             = 5 * time.Second
	DefaultIdleTTL            time.Duration             = 10 * time.Second
	DefaultNormalizationFlags purell.NormalizationFlags = purell.FlagsAllGreedy
)

Default options

Variables

View Source 
var HttpClient = &http.Client{CheckRedirect: func(req *http.Request, via []*http.Request) error {

	if isRobotsTxtUrl(req.URL) {
		if len(via) >= 10 {
			return errors.New("stopped after 10 redirects")
		}
		return nil
	}

	return &EnqueueRedirectError{"redirection not followed"}
}}

The default HTTP client used by DefaultExtender's fetch requests (this is thread-safe). The client's fields can be customized (i.e. for a different redirection strategy, a different Transport object, ...). It should be done prior to starting the crawler.

Functions

This section is empty.

Types

type CrawlError 

type CrawlError struct {
	Err  error
	Kind CrawlErrorKind
	URL  *url.URL
	// contains filtered or unexported fields
}

Crawl error information.

func (CrawlError) Error 

func (this CrawlError) Error() string

Implementation of the error interface.

type CrawlErrorKind 

type CrawlErrorKind uint8

Flag indicating the source of the crawl error. 

const (
	CekFetch CrawlErrorKind = iota
	CekParseRobots
	CekHttpStatusCode
	CekReadBody
	CekParseBody
	CekParseSeed
	CekParseNormalizedSeed
	CekProcessLinks
	CekParseRedirectUrl
)

type Crawler 

type Crawler struct {
	Options *Options
	// contains filtered or unexported fields
}

The crawler itself, the master of the whole process

func NewCrawler 

func NewCrawler(ext Extender) *Crawler

Crawler constructor with the specified extender object.

func NewCrawlerWithOptions 

func NewCrawlerWithOptions(opts *Options) *Crawler

Crawler constructor with a pre-initialized Options object.

func (*Crawler) Run 

func (this *Crawler) Run(seeds ...string) EndReason

Run starts the crawling process, based on the given seeds and the current Options settings. Execution stops either when MaxVisits is reached (if specified) or when no more URLs need visiting.

type CrawlerCommand 

type CrawlerCommand struct {
	URL    *url.URL
	Origin EnqueueOrigin
}

Communication from extender to crawler about an URL to enqueue

type DefaultExtender 

type DefaultExtender struct {
	EnqueueChan chan<- *CrawlerCommand
}

Default working implementation of an extender.

func (*DefaultExtender) ComputeDelay 

func (this *DefaultExtender) ComputeDelay(host string, di *DelayInfo, lastFetch *FetchInfo) time.Duration

ComputeDelay returns the delay specified in the Crawler's Options, unless a crawl-delay is specified in the robots.txt file, which has precedence.

func (*DefaultExtender) Disallowed 

func (this *DefaultExtender) Disallowed(u *url.URL)

Disallowed is a no-op.

func (*DefaultExtender) End 

func (this *DefaultExtender) End(reason EndReason)

End is a no-op.

func (*DefaultExtender) Enqueued 

func (this *DefaultExtender) Enqueued(u *url.URL, from *url.URL)

Enqueued is a no-op.

func (*DefaultExtender) Error 

func (this *DefaultExtender) Error(err *CrawlError)

Error is a no-op (logging is done automatically, regardless of the implementation of the Error() hook).

func (*DefaultExtender) Fetch 

func (this *DefaultExtender) Fetch(u *url.URL, userAgent string, headRequest bool) (*http.Response, error)

Fetch requests the specified URL using the given user agent string. It uses a custom http Client instance that doesn't follow redirections. Instead, the redirected-to URL is enqueued so that it goes through the same Filter() and Fetch() process as any other URL.

Two options were considered for the default Fetch() implementation : 1- Not following any redirections, and enqueuing the redirect-to URL, 

failing the current call with the 3xx status code.

2- Following all redirections, enqueuing only the last one (where redirection 

stops). Returning the response of the next-to-last request.

Ultimately, 1) was implemented, as it is the most generic solution that makes sense as default for the library. It involves no "magic" and gives full control as to what can happen, with the disadvantage of having the Filter() being aware of all possible intermediary URLs before reaching the final destination of a redirection (i.e. if A redirects to B that redirects to C, Filter has to allow A, B, and C to be Fetched, while solution 2 would only have required Filter to allow A and C).

Solution 2) also has the disadvantage of fetching twice the final URL (once while processing the original URL, so that it knows that there is no more redirection HTTP code, and another time when the actual destination URL is fetched to be visited).

func (*DefaultExtender) FetchedRobots 

func (this *DefaultExtender) FetchedRobots(res *http.Response)

FetchedRobots is a no-op.

func (*DefaultExtender) Filter 

func (this *DefaultExtender) Filter(u *url.URL, from *url.URL, isVisited bool, origin EnqueueOrigin) (enqueue bool, priority int, headRequest HeadRequestMode)

Enqueue the URL if it hasn't been visited yet.

func (*DefaultExtender) Log 

func (this *DefaultExtender) Log(logFlags LogFlags, msgLevel LogFlags, msg string)

Log prints to the standard error by default, based on the requested log verbosity.

func (*DefaultExtender) RequestGet 

func (this *DefaultExtender) RequestGet(headRes *http.Response) bool

Ask the worker to actually request the URL's body (issue a GET), unless the status code is not 2xx.

func (*DefaultExtender) RequestRobots 

func (this *DefaultExtender) RequestRobots(u *url.URL, robotAgent string) (request bool, data []byte)

Ask the worker to actually request (fetch) the Robots.txt document.

func (*DefaultExtender) Start 

func (this *DefaultExtender) Start(seeds []string) []string

Return the same seeds as those received (those that were passed to Run() initially).

func (*DefaultExtender) Visit 

func (this *DefaultExtender) Visit(res *http.Response, doc *goquery.Document) (harvested []*url.URL, findLinks bool)

Ask the worker to harvest the links in this page.

func (*DefaultExtender) Visited 

func (this *DefaultExtender) Visited(u *url.URL, harvested []*url.URL)

Visited is a no-op.

type DelayInfo 

type DelayInfo struct {
	OptsDelay   time.Duration
	RobotsDelay time.Duration
	LastDelay   time.Duration
}

Delay information: the Options delay, the Robots.txt delay, and the last delay used.

type EndReason 

type EndReason uint8

Flag indicating why the crawler ended. 

const (
	ErDone EndReason = iota
	ErMaxVisits
	ErError
)

type EnqueueOrigin 

type EnqueueOrigin int

EnqueueOrigin indicates to the crawler and the Filter extender function the origin of this URL. 

const (
	EoSeed        EnqueueOrigin = iota // Seed URLs have this source
	EoHarvest                          // URLs harvested from a visit to a page have this source
	EoRedirect                         // URLs enqueued from a fetch redirection have this source by default
	EoError                            // URLs enqueued after an error
	EoCustomStart                      // Custom EnqueueOrigins should start at this value instead of iota
)

type EnqueueRedirectError 

type EnqueueRedirectError struct {
	// contains filtered or unexported fields
}

The error type returned when a redirection is requested, so that the worker knows that this is not an actual Fetch error, but a request to enqueue the redirect-to URL.

func (*EnqueueRedirectError) Error 

func (this *EnqueueRedirectError) Error() string

Implement the error interface

type Extender 

type Extender interface {
	Start([]string) []string
	End(EndReason)
	Error(*CrawlError)
	Log(LogFlags, LogFlags, string)

	ComputeDelay(string, *DelayInfo, *FetchInfo) time.Duration
	Fetch(*url.URL, string, bool) (*http.Response, error)
	RequestGet(*http.Response) bool
	RequestRobots(*url.URL, string) (bool, []byte)
	FetchedRobots(*http.Response)

	Filter(*url.URL, *url.URL, bool, EnqueueOrigin) (bool, int, HeadRequestMode)
	Enqueued(*url.URL, *url.URL)
	Visit(*http.Response, *goquery.Document) ([]*url.URL, bool)
	Visited(*url.URL, []*url.URL)
	Disallowed(*url.URL)
}

Extension methods required to provide an extender instance.

type FetchInfo 

type FetchInfo struct {
	Duration      time.Duration
	StatusCode    int
	HeadRequest   bool
	RobotsRequest bool
}

Fetch information: the duration of the fetch, the returned status code, whether or not it was a HEAD request, and whether or not it was a robots.txt request.

type HeadRequestMode 

type HeadRequestMode uint8

Flag indicating the head request override mode 

const (
	HrmDefault HeadRequestMode = iota
	HrmRequest
	HrmIgnore
)

type LogFlags 

type LogFlags uint
const (
	LogError LogFlags = 1 << iota
	LogInfo
	LogEnqueued
	LogIgnored
	LogTrace
	LogNone LogFlags = 0
	LogAll  LogFlags = LogError | LogInfo | LogEnqueued | LogIgnored | LogTrace
)

Log levels for the library's logger

type Options 

type Options struct {
	UserAgent             string
	RobotUserAgent        string
	MaxVisits             int
	EnqueueChanBuffer     int
	HostBufferFactor      int
	CrawlDelay            time.Duration // Applied per host
	WorkerIdleTTL         time.Duration
	SameHostOnly          bool
	HeadBeforeGet         bool
	URLNormalizationFlags purell.NormalizationFlags
	LogFlags              LogFlags
	Extender              Extender
}

The Options available to control and customize the crawling process.

func NewOptions 

func NewOptions(ext Extender) *Options

Source Files

View all Source files

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