go-crawler, v1.1

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

Repeated extracting of relative links and parallelization possibilities of crawling.

Change Log

• repeated extracting of relative links on error (optional):
  • only specified repeat count;
  • supporting of delay between repeats;
• parallelization possibilities:
  • crawling of relative links in parallel;
  • simulate an unbounded channel of links to avoid a deadlock.

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;
• calling of an outer handler for an each found link:
  • it's called directly during crawling;
• custom filtering of considered links:
  • by relativity of a link (optional);
• 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():

package main

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

    "github.com/go-log/log/print"
    crawler "github.com/thewizardplusplus/go-crawler"
    "github.com/thewizardplusplus/go-crawler/checkers"
    "github.com/thewizardplusplus/go-crawler/extractors"
    htmlselector "github.com/thewizardplusplus/go-html-selector"
)

type LinkHandler struct {
    ServerURL string
}

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

    fmt.Printf("have got the link: %s\n", link)
}

func main() {
    server := httptest.NewServer(http.HandlerFunc(func(
        writer http.ResponseWriter,
        request *http.Request,
    ) {
        if request.URL.Path != "/" {
            return
        }

        fmt.Fprintf( // nolint: errcheck
            writer,
            `<ul>
                <li><a href="http://%[1]s/1">1</a></li>
                <li><a href="http://%[1]s/2">2</a></li>
            </ul>`,
            request.Host,
        )
    }))
    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.Dependencies{
            Waiter: &waiter,
            LinkExtractor: extractors.RepeatingExtractor{
                LinkExtractor: extractors.DefaultExtractor{
                    HTTPClient: http.DefaultClient,
                    Filters: htmlselector.OptimizeFilters(htmlselector.FilterGroup{
                        "a": {"href"},
                    }),
                },
                RepeatCount: 5,
                RepeatDelay: time.Second,
                Logger:         wrappedLogger,
            },
            LinkChecker: checkers.HostChecker{
                Logger: wrappedLogger,
            },
            LinkHandler: LinkHandler{
                ServerURL: server.URL,
            },
            Logger: wrappedLogger,
        },
    )

    waiter.Wait()

    // Unordered output:
    // have got the link: http://example.com
    // have got the link: http://example.com/1
    // have got the link: http://example.com/2
}

Repository

Link: https://github.com/thewizardplusplus/go-crawler/tree/v1.1.

Content: code.

License: MIT.