feat: SlickVPN Support (#961)

- `internal/updater/html` package
- Add unit tests for slickvpn updating code
- Change shared html package to be more share-able
- Split html utilities in multiple files
- Fix processing .ovpn files with prefix space

Authored by @Rohaq 
Co-authored-by: Quentin McGaw <quentin.mcgaw@gmail.com>

internal/updater/html/attribute.go

@@ -0,0 +1,12 @@
+package html
+
+import "golang.org/x/net/html"
+
+func Attribute(node *html.Node, key string) (value string) {
+	for _, attribute := range node.Attr {
+		if attribute.Key == key {
+			return attribute.Val
+		}
+	}
+	return ""
+}

internal/updater/html/bfs.go

@@ -0,0 +1,43 @@
+package html
+
+import (
+	"container/list"
+	"fmt"
+
+	"golang.org/x/net/html"
+)
+
+// BFS returns the node matching the match function and nil
+// if no node is found.
+func BFS(rootNode *html.Node, match MatchFunc) (node *html.Node) {
+	visited := make(map[*html.Node]struct{})
+	queue := list.New()
+	_ = queue.PushBack(rootNode)
+
+	for queue.Len() > 0 {
+		listElement := queue.Front()
+		node, ok := queue.Remove(listElement).(*html.Node)
+		if !ok {
+			panic(fmt.Sprintf("linked list has bad type %T", listElement.Value))
+		}
+
+		if node == nil {
+			continue
+		}
+
+		if _, ok := visited[node]; ok {
+			continue
+		}
+		visited[node] = struct{}{}
+
+		if match(node) {
+			return node
+		}
+
+		for child := node.FirstChild; child != nil; child = child.NextSibling {
+			_ = queue.PushBack(child)
+		}
+	}
+
+	return nil
+}

internal/updater/html/css.go

@@ -0,0 +1,22 @@
+package html
+
+import (
+	"strings"
+
+	"golang.org/x/net/html"
+)
+
+func HasClassStrings(node *html.Node, classStrings ...string) (match bool) {
+	targetClasses := make(map[string]struct{}, len(classStrings))
+	for _, classString := range classStrings {
+		targetClasses[classString] = struct{}{}
+	}
+
+	classAttribute := Attribute(node, "class")
+	classes := strings.Fields(classAttribute)
+	for _, class := range classes {
+		delete(targetClasses, class)
+	}
+
+	return len(targetClasses) == 0
+}

internal/updater/html/errors.go

@@ -0,0 +1,27 @@
+package html
+
+import (
+	"bytes"
+	"fmt"
+
+	"golang.org/x/net/html"
+)
+
+func WrapError(sentinelError error, node *html.Node) error {
+	return fmt.Errorf("%w: in HTML code: %s",
+		sentinelError, mustRenderHTML(node))
+}
+
+func WrapWarning(warning string, node *html.Node) string {
+	return fmt.Sprintf("%s: in HTML code: %s",
+		warning, mustRenderHTML(node))
+}
+
+func mustRenderHTML(node *html.Node) (rendered string) {
+	stringBuffer := bytes.NewBufferString("")
+	err := html.Render(stringBuffer, node)
+	if err != nil {
+		panic(err)
+	}
+	return stringBuffer.String()
+}

internal/updater/html/match.go

@@ -0,0 +1,43 @@
+package html
+
+import (
+	"golang.org/x/net/html"
+)
+
+type MatchFunc func(node *html.Node) (match bool)
+
+func MatchID(id string) MatchFunc {
+	return func(node *html.Node) (match bool) {
+		if node == nil {
+			return false
+		}
+
+		return Attribute(node, "id") == id
+	}
+}
+
+func MatchData(data string) MatchFunc {
+	return func(node *html.Node) (match bool) {
+		return node != nil && node.Type == html.ElementNode && node.Data == data
+	}
+}
+
+func DirectChild(parent *html.Node,
+	matchFunc MatchFunc) (child *html.Node) {
+	for child := parent.FirstChild; child != nil; child = child.NextSibling {
+		if matchFunc(child) {
+			return child
+		}
+	}
+	return nil
+}
+
+func DirectChildren(parent *html.Node,
+	matchFunc MatchFunc) (children []*html.Node) {
+	for child := parent.FirstChild; child != nil; child = child.NextSibling {
+		if matchFunc(child) {
+			children = append(children, child)
+		}
+	}
+	return children
+}