go-crawler, v1.7

The library that implements crawling of all relative links for specified ones.

Supporting of grouping of link extractors and extracting links from a sitemap.xml file (optional).

Change Log

• crawling of all relative links for specified ones:
  • extracting links from a sitemap.xml file (optional):
    • supporting of few sitemap.xml files for a single link;
    • supporting of a Sitemap index file;
    • supporting of a delay before loading of a specific sitemap.xml file;
  • supporting of grouping of link extractors:
    • result of group extracting is merged results of each extractor in the group.

Features

• crawling of all relative links for specified ones:
  • repeated extracting of relative links on error (optional):
    • only specified repeat count;
    • supporting of delay between repeats;
  • delayed extracting of relative links (optional):
    • reducing of a delay time by the time elapsed since the last request;
    • using of individual delays for each thread;
  • extracting links from a sitemap.xml file (optional):
    • supporting of few sitemap.xml files for a single link;
    • supporting of a Sitemap index file;
    • supporting of a delay before loading of a specific sitemap.xml file;
  • supporting of grouping of link extractors:
    • result of group extracting is merged results of each extractor in the group;
• calling of an outer handler for an each found link:
  • it's called directly during crawling;
  • handling of links immediately after they have been extracted;
  • passing of the source link in the outer handler;
  • handling links filtered by a custom link filter (optional);
  • handling links concurrently (optional);
• custom filtering of considered links:
  • by relativity of a link (optional);
  • by uniqueness of an extracted link (optional):
    • supporting of sanitizing of a link before checking of uniqueness (optional);
  • by a robots.txt file (optional):
    • customized user agent;
  • supporting of grouping of link filters:
    • result of group filtering is successful only when all filters are successful;
• parallelization possibilities:
  • crawling of relative links in parallel;
  • supporting of background working:
    • automatic completion after processing all filtered links;
  • simulate an unbounded channel of links to avoid a deadlock.

Examples

crawler.HandleLinksConcurrently() with processing a sitemap.xml file:

package main

import (
    "context"
    "fmt"
    "io"
    stdlog "log"
    "net/http"
    "net/http/httptest"
    "os"
    "path"
    "runtime"
    "strings"
    "sync"
    "text/template"
    "time"

    "github.com/go-log/log/print"
    "github.com/thewizardplusplus/go-crawler"
    "github.com/thewizardplusplus/go-crawler/checkers"
    "github.com/thewizardplusplus/go-crawler/extractors"
    "github.com/thewizardplusplus/go-crawler/handlers"
    "github.com/thewizardplusplus/go-crawler/models"
    "github.com/thewizardplusplus/go-crawler/registers"
    "github.com/thewizardplusplus/go-crawler/registers/sitemap"
    "github.com/thewizardplusplus/go-crawler/sanitizing"
    htmlselector "github.com/thewizardplusplus/go-html-selector"
)

type LinkHandler struct {
    ServerURL string
}

func (handler LinkHandler) HandleLink(
    ctx context.Context,
    link models.SourcedLink,
) {
    fmt.Printf(
        "have got the link %q from the page %q\n",
        handler.replaceServerURL(link.Link),
        handler.replaceServerURL(link.SourceLink),
    )
}

// replace the test server URL for reproducibility of the example
func (handler LinkHandler) replaceServerURL(link string) string {
    return strings.Replace(link, handler.ServerURL, "http://example.com", -1)
}

func RunServer() *httptest.Server {
    return httptest.NewServer(http.HandlerFunc(func(
        writer http.ResponseWriter,
        request *http.Request,
    ) {
        if request.URL.Path == "/robots.txt" {
            // nolint: errcheck
            fmt.Fprint(writer, `
                User-agent: go-crawler
                Disallow: /2
            `)

            return
        }

        if request.URL.Path == "/sitemap.xml" {
            links := []string{"/1", "/2", "/hidden/1", "/hidden/2"}
            completeLinksWithHost(links, request.Host)

            // nolint: errcheck
            renderTemplate(writer, links, `
                <?xml version="1.0" encoding="UTF-8" ?>
                <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
                    {{ range $link := . }}
                        <url>
                            <loc>{{ $link }}</loc>
                        </url>
                    {{ end }}
                </urlset>
            `)

            return
        }

        var links []string
        switch request.URL.Path {
        case "/":
            links = []string{"/1", "/2", "/2", "https://golang.org/"}
        case "/1":
            links = []string{"/1/1", "/1/2"}
        case "/2":
            links = []string{"/2/1", "/2/2"}
        }
        completeLinksWithHost(links, request.Host)

        // nolint: errcheck
        renderTemplate(writer, links, `
            <ul>
                {{ range $link := . }}
                    <li>
                        <a href="{{ $link }}">{{ $link }}</a>
                    </li>
                {{ end }}
            </ul>
        `)
    }))
}

func completeLinksWithHost(links []string, host string) {
    for index := range links {
        if strings.HasPrefix(links[index], "/") {
            links[index] = "http://" + path.Join(host, links[index])
        }
    }
}

func renderTemplate(writer io.Writer, data interface{}, text string) error {
    template, err := template.New("").Parse(text)
    if err != nil {
        return err
    }

    return template.Execute(writer, data)
}

func main() {
    server := RunServer()
    defer server.Close()

    links := make(chan string, 1000)
    links <- server.URL

    var waiter sync.WaitGroup
    waiter.Add(1)

    logger := stdlog.New(os.Stderr, "", stdlog.LstdFlags|stdlog.Lmicroseconds)
    // wrap the standard logger via the github.com/go-log/log package
    wrappedLogger := print.New(logger)

    crawler.HandleLinksConcurrently(
        context.Background(),
        runtime.NumCPU(),
        links,
        crawler.HandleLinkDependencies{
            CrawlDependencies: crawler.CrawlDependencies{
                LinkExtractor: extractors.RepeatingExtractor{
                    LinkExtractor: extractors.ExtractorGroup{
                        extractors.DefaultExtractor{
                            HTTPClient: http.DefaultClient,
                            Filters: htmlselector.OptimizeFilters(htmlselector.FilterGroup{
                                "a": {"href"},
                            }),
                        },
                        extractors.SitemapExtractor{
                            SitemapRegister: registers.NewSitemapRegister(
                                time.Second,
                                sitemap.SimpleLinkGenerator{},
                                wrappedLogger,
                                time.Sleep,
                                nil,
                            ),
                            Logger: wrappedLogger,
                        },
                    },
                    RepeatCount:  5,
                    RepeatDelay:  time.Second,
                    Logger:       wrappedLogger,
                    SleepHandler: time.Sleep,
                },
                LinkChecker: checkers.CheckerGroup{
                    checkers.HostChecker{
                        Logger: wrappedLogger,
                    },
                    checkers.DuplicateChecker{
                        LinkRegister: registers.NewLinkRegister(
                            sanitizing.SanitizeLink,
                            wrappedLogger,
                        ),
                    },
                },
                LinkHandler: handlers.CheckedHandler{
                    LinkChecker: checkers.DuplicateChecker{
                        // don't use here the link register from the duplicate checker above
                        LinkRegister: registers.NewLinkRegister(
                            sanitizing.SanitizeLink,
                            wrappedLogger,
                        ),
                    },
                    LinkHandler: LinkHandler{
                        ServerURL: server.URL,
                    },
                },
                Logger: wrappedLogger,
            },
            Waiter: &waiter,
        },
    )

    waiter.Wait()

    // Unordered output:
    // have got the link "http://example.com/1" from the page "http://example.com"
    // have got the link "http://example.com/1/1" from the page "http://example.com/1"
    // have got the link "http://example.com/1/2" from the page "http://example.com/1"
    // have got the link "http://example.com/2" from the page "http://example.com"
    // have got the link "http://example.com/2/1" from the page "http://example.com/2"
    // have got the link "http://example.com/2/2" from the page "http://example.com/2"
    // have got the link "http://example.com/hidden/1" from the page "http://example.com"
    // have got the link "http://example.com/hidden/2" from the page "http://example.com"
    // have got the link "https://golang.org/" from the page "http://example.com"
}

Repository

Link: https://github.com/thewizardplusplus/go-crawler/tree/v1.7.

Content: code.

License: MIT.