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|
package main
import (
"context"
"flag"
"fmt"
"log"
"net/url"
)
func main() {
maxConcurrency := flag.Int("c", 0, "Maximum number of concurrent queue pushes")
startRawURL := flag.String("url", "", "Entry-point URL")
flag.Parse()
if *maxConcurrency == 0 {
log.Fatal("Missing -c argument")
}
if *startRawURL == "" {
log.Fatal("Missing -url argument")
}
startURL, err := url.Parse(*startRawURL)
if err != nil {
log.Fatal(err)
}
/* Main logic starts here. */
worklist := make(chan []url.URL)
go func() {
worklist <- []url.URL{*startURL}
}()
sem := make(chan struct{}, *maxConcurrency)
ctx, cancel := context.WithCancel(context.Background())
seen := make(map[url.URL]bool)
i := 1
loop:
for list := range worklist {
for _, u := range list {
if len(seen) == 30 {
cancel()
break loop
}
if !seen[u] {
fmt.Printf("%d. %s\n", i, &u)
i++
seen[u] = true
go func() {
sem <- struct{}{}
defer func() { <-sem }()
worklist <- crawl(ctx, u)
}()
}
}
}
}
func crawl(ctx context.Context, u url.URL) []url.URL {
select {
case <-ctx.Done():
return nil
default:
}
doc, err := fetch(u)
if err != nil {
log.Print(err)
return nil
}
return findURLs(u, doc)
}
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