1 files changed, 191 insertions, 0 deletions
diff --git a/misc/linkcheck/linkcheck.go b/misc/linkcheck/linkcheck.go
new file mode 100644
index 0000000..efe4009
--- /dev/null
+++ b/misc/linkcheck/linkcheck.go
@@ -0,0 +1,191 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The linkcheck command finds missing links in the godoc website.
+// It crawls a URL recursively and notes URLs and URL fragments
+// that it's seen and prints a report of missing links at the end.
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"regexp"
+	"strings"
+	"sync"
+)
+
+var (
+	root    = flag.String("root", "http://localhost:6060", "Root to crawl")
+	verbose = flag.Bool("verbose", false, "verbose")
+)
+
+var wg sync.WaitGroup        // outstanding fetches
+var urlq = make(chan string) // URLs to crawl
+
+// urlFrag is a URL and its optional #fragment (without the #)
+type urlFrag struct {
+	url, frag string
+}
+
+var (
+	mu          sync.Mutex
+	crawled     = make(map[string]bool)      // URL without fragment -> true
+	neededFrags = make(map[urlFrag][]string) // URL#frag -> who needs it
+)
+
+var aRx = regexp.MustCompile(`<a href=['"]?(/[^\s'">]+)`)
+
+// Owned by crawlLoop goroutine:
+var (
+	linkSources = make(map[string][]string) // url no fragment -> sources
+	fragExists  = make(map[urlFrag]bool)
+	problems    []string
+)
+
+func localLinks(body string) (links []string) {
+	seen := map[string]bool{}
+	mv := aRx.FindAllStringSubmatch(body, -1)
+	for _, m := range mv {
+		ref := m[1]
+		if strings.HasPrefix(ref, "/src/") {
+			continue
+		}
+		if !seen[ref] {
+			seen[ref] = true
+			links = append(links, m[1])
+		}
+	}
+	return
+}
+
+var idRx = regexp.MustCompile(`\bid=['"]?([^\s'">]+)`)
+
+func pageIDs(body string) (ids []string) {
+	mv := idRx.FindAllStringSubmatch(body, -1)
+	for _, m := range mv {
+		ids = append(ids, m[1])
+	}
+	return
+}
+
+// url may contain a #fragment, and the fragment is then noted as needing to exist.
+func crawl(url string, sourceURL string) {
+	if strings.Contains(url, "/devel/release") {
+		return
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if u, frag, ok := strings.Cut(url, "#"); ok {
+		url = u
+		if frag != "" {
+			uf := urlFrag{url, frag}
+			neededFrags[uf] = append(neededFrags[uf], sourceURL)
+		}
+	}
+	if crawled[url] {
+		return
+	}
+	crawled[url] = true
+
+	wg.Add(1)
+	go func() {
+		urlq <- url
+	}()
+}
+
+func addProblem(url, errmsg string) {
+	msg := fmt.Sprintf("Error on %s: %s (from %s)", url, errmsg, linkSources[url])
+	if *verbose {
+		log.Print(msg)
+	}
+	problems = append(problems, msg)
+}
+
+func crawlLoop() {
+	for url := range urlq {
+		if err := doCrawl(url); err != nil {
+			addProblem(url, err.Error())
+		}
+	}
+}
+
+func doCrawl(url string) error {
+	defer wg.Done()
+
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return err
+	}
+	res, err := http.DefaultTransport.RoundTrip(req)
+	if err != nil {
+		return err
+	}
+	// Handle redirects.
+	if res.StatusCode/100 == 3 {
+		newURL, err := res.Location()
+		if err != nil {
+			return fmt.Errorf("resolving redirect: %v", err)
+		}
+		if !strings.HasPrefix(newURL.String(), *root) {
+			// Skip off-site redirects.
+			return nil
+		}
+		crawl(newURL.String(), url)
+		return nil
+	}
+	if res.StatusCode != 200 {
+		return errors.New(res.Status)
+	}
+	slurp, err := io.ReadAll(res.Body)
+	res.Body.Close()
+	if err != nil {
+		log.Fatalf("Error reading %s body: %v", url, err)
+	}
+	if *verbose {
+		log.Printf("Len of %s: %d", url, len(slurp))
+	}
+	body := string(slurp)
+	for _, ref := range localLinks(body) {
+		if *verbose {
+			log.Printf("  links to %s", ref)
+		}
+		dest := *root + ref
+		linkSources[dest] = append(linkSources[dest], url)
+		crawl(dest, url)
+	}
+	for _, id := range pageIDs(body) {
+		if *verbose {
+			log.Printf(" url %s has #%s", url, id)
+		}
+		fragExists[urlFrag{url, id}] = true
+	}
+	return nil
+}
+
+func main() {
+	flag.Parse()
+
+	go crawlLoop()
+	crawl(*root, "")
+
+	wg.Wait()
+	close(urlq)
+	for uf, needers := range neededFrags {
+		if !fragExists[uf] {
+			problems = append(problems, fmt.Sprintf("Missing fragment for %+v from %v", uf, needers))
+		}
+	}
+
+	for _, s := range problems {
+		fmt.Println(s)
+	}
+	if len(problems) > 0 {
+		os.Exit(1)
+	}
+}