From 62c62b5c339434a7c2edaa8a4e3012ec1c7aaa52 Mon Sep 17 00:00:00 2001
From: kjuulh <contact@kjuulh.io>
Date: Wed, 23 Feb 2022 03:22:24 +0100
Subject: [PATCH] Add linkchecker

---
 linkchecker/go.mod                     |   5 +
 linkchecker/go.sum                     |   2 +
 linkchecker/linkchecker/linkchecker.go | 184 +++++++++++++++++++++++++
 linkchecker/main.go                    |  14 ++
 4 files changed, 205 insertions(+)
 create mode 100644 linkchecker/go.mod
 create mode 100644 linkchecker/go.sum
 create mode 100644 linkchecker/linkchecker/linkchecker.go
 create mode 100644 linkchecker/main.go

diff --git a/linkchecker/go.mod b/linkchecker/go.mod
new file mode 100644
index 0000000..6bfba6b
--- /dev/null
+++ b/linkchecker/go.mod
@@ -0,0 +1,5 @@
+module linkchecker
+
+go 1.17
+
+require golang.org/x/net v0.0.0-20220127200216-cd36cc0744dd // indirect
diff --git a/linkchecker/go.sum b/linkchecker/go.sum
new file mode 100644
index 0000000..aff97b6
--- /dev/null
+++ b/linkchecker/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/net v0.0.0-20220127200216-cd36cc0744dd h1:O7DYs+zxREGLKzKoMQrtrEacpb0ZVXA5rIwylE2Xchk=
+golang.org/x/net v0.0.0-20220127200216-cd36cc0744dd/go.mod h1:CfG3xpIq0wQ8r1q4Su4UZFWDARRcnwPjda9FqA0JpMk=
diff --git a/linkchecker/linkchecker/linkchecker.go b/linkchecker/linkchecker/linkchecker.go
new file mode 100644
index 0000000..1ec9244
--- /dev/null
+++ b/linkchecker/linkchecker/linkchecker.go
@@ -0,0 +1,184 @@
+package linkchecker
+
+import (
+	"errors"
+	"golang.org/x/net/html"
+	"log"
+	"net/http"
+	"sync"
+)
+
+const (
+	NotScanned = iota
+	Success
+	Broken
+)
+
+type Link struct {
+	Url        string
+	links      []*Link
+	Status     uint64
+	StatusCode int
+	Parent     *Link
+}
+
+type LinkChecker struct {
+	link *Link
+}
+
+func New(url string) *LinkChecker {
+	return &LinkChecker{
+		link: &Link{
+			Url:    url,
+			links:  make([]*Link, 0),
+			Status: NotScanned,
+			Parent: nil,
+		},
+	}
+}
+
+func (c *LinkChecker) Scan(depth uint64) {
+	wg := &sync.WaitGroup{}
+
+	c.link.Scan(depth, wg)
+
+	wg.Wait()
+}
+
+func (c *LinkChecker) Print() {
+	log.Printf("linkcheck %s", c.link.Url)
+
+	// Stats
+	scanned := c.link.collectScanned()
+	broken := make([]*Link, 0)
+	c.link.collectBroken(&broken)
+	log.Printf("%d links scanned, %d broken links found", scanned, len(broken))
+
+	for i, brokenLink := range broken {
+		if brokenLink.Parent != nil {
+			log.Printf("%d. Source page: %s", i+1, brokenLink.Parent.Url)
+		} else {
+			log.Printf("%d", i+1)
+		}
+		if brokenLink.StatusCode != 0 {
+			log.Printf("Target: %s (status: %d)", brokenLink.Url, brokenLink.StatusCode)
+		} else {
+			log.Printf("Target: %s (status: Unknown error occurred)", brokenLink.Url)
+		}
+	}
+}
+
+func (l *Link) Scan(depth uint64, wg *sync.WaitGroup) {
+	if depth == 0 {
+		return
+	}
+	wg.Add(1)
+	defer wg.Done()
+
+	log.Printf("Calling: %s\n", l.Url)
+	response, err := http.Get(l.Url)
+	if err != nil {
+		l.Status = Broken
+		return
+	}
+	defer response.Body.Close()
+
+	l.StatusCode = response.StatusCode
+	if response.StatusCode > 299 {
+		log.Printf("Status was broken for: %s\n", l.Url)
+		l.Status = Broken
+		return
+	}
+	l.Status = Success
+
+	//	log.Printf("Getting outgoing links for: %s\n", l.Url)
+	links := getAllOutgoingLinks(response)
+	l.links = links
+	for _, link := range links {
+		link.Parent = l
+		go link.Scan(depth-1, wg)
+	}
+
+}
+
+func (l *Link) collectScanned() int {
+	if l.Status == NotScanned {
+		return 0
+	}
+
+	if l.Status == Broken {
+		return 1
+	}
+
+	sumOfChildrenScans := 0
+	for _, link := range l.links {
+		sumOfChildrenScans += link.collectScanned()
+	}
+
+	return 1 + sumOfChildrenScans
+}
+
+func (l *Link) collectBroken(brokenLinks *[]*Link) {
+	if l.Status == NotScanned {
+		return
+	}
+
+	if l.Status == Broken {
+		*brokenLinks = append(*brokenLinks, l)
+		return
+	}
+
+	for _, link := range l.links {
+		link.collectBroken(brokenLinks)
+	}
+}
+
+func traverse(n *html.Node, links *[]*Link) {
+	if l, err := checkLink(n); err == nil {
+		//		log.Printf("Found link: %s\n", l.Url)
+		*links = append(*links, l)
+	}
+
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		traverse(c, links)
+	}
+}
+
+func checkLink(n *html.Node) (*Link, error) {
+	if n.Type == html.ElementNode && n.Data == "a" {
+		s, ok := getLinkElementWithSource(n)
+		if ok {
+			if len(s) > 0 && (s[0] == '/' || s[0] == '#') {
+				return nil, errors.New("local url, cannot continue")
+			}
+			return &Link{
+				Url:    s,
+				links:  make([]*Link, 0),
+				Status: 0,
+			}, nil
+		}
+	}
+
+	return nil, errors.New("was not an element")
+}
+
+func getLinkElementWithSource(n *html.Node) (string, bool) {
+	for _, attr := range n.Attr {
+		if attr.Key == "href" {
+			return attr.Val, true
+		}
+	}
+	return "", false
+}
+
+func getAllOutgoingLinks(response *http.Response) []*Link {
+	doc, err := html.Parse(response.Body)
+	if err != nil {
+		return nil
+	}
+
+	links := make([]*Link, 0)
+	traverse(doc, &links)
+
+	return links
+}
diff --git a/linkchecker/main.go b/linkchecker/main.go
new file mode 100644
index 0000000..6ca0a37
--- /dev/null
+++ b/linkchecker/main.go
@@ -0,0 +1,14 @@
+package main
+
+import "linkchecker/linkchecker"
+
+func main() {
+	lc := linkchecker.New("https://bitfieldconsulting.com/golang/how")
+	//lc := linkchecker.New("https://example.com")
+	//lc := linkchecker.New("https://www.aksjhdfjkhashjkd.com/")
+	//lc := linkchecker.New("https://lamehackersguide.blogspot.com/2017/02/weaponizing-postscript.html")
+
+	lc.Scan(3)
+
+	lc.Print()
+}