feat: initial goget release — modern IPv6-first download utility

internal/linkrewrite/rewriter.go

@@ -0,0 +1,143 @@
+//go:build linux || freebsd
+// +build linux freebsd
+
+// Package linkrewrite rewrites HTML links for local offline viewing.
+package linkrewrite
+
+import (
+	"net/url"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"golang.org/x/net/html"
+)
+
+// Rewriter converts absolute URLs in HTML to local relative paths.
+type Rewriter struct {
+	baseURL   *url.URL
+	outputDir string
+	visited   map[string]string
+	visitedMu sync.RWMutex
+}
+
+// New creates a link rewriter for a mirror or recursive download.
+func New(baseURL *url.URL, outputDir string) *Rewriter {
+	return &Rewriter{
+		baseURL:   baseURL,
+		outputDir: outputDir,
+		visited:   make(map[string]string),
+	}
+}
+
+// Register records a downloaded URL and its local path.
+func (lr *Rewriter) Register(u *url.URL, localPath string) {
+	lr.visitedMu.Lock()
+	defer lr.visitedMu.Unlock()
+	lr.visited[u.String()] = localPath
+}
+
+// RewriteLinks converts URLs in an HTML document to local paths.
+func (lr *Rewriter) RewriteLinks(doc *html.Node, filePath string) int {
+	converted := 0
+	dir := filepath.Dir(filePath)
+
+	var traverse func(*html.Node)
+	traverse = func(n *html.Node) {
+		if n.Type == html.ElementNode {
+			switch n.Data {
+			case "a":
+				converted += lr.rewriteAttr(n, "href", dir)
+			case "img", "script", "iframe", "video", "audio", "source", "track", "embed", "object":
+				converted += lr.rewriteAttr(n, "src", dir)
+			case "link":
+				converted += lr.rewriteAttr(n, "href", dir)
+			case "form":
+				converted += lr.rewriteAttr(n, "action", dir)
+			case "area":
+				converted += lr.rewriteAttr(n, "href", dir)
+			case "meta":
+				for _, attr := range n.Attr {
+					if attr.Key == "content" && strings.Contains(attr.Val, "url=") {
+						converted += lr.rewriteMetaRefresh(n, dir)
+					}
+					if attr.Key == "property" && strings.Contains(attr.Val, "image") {
+						converted += lr.rewriteAttr(n, "content", dir)
+					}
+				}
+			}
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			traverse(c)
+		}
+	}
+
+	traverse(doc)
+	return converted
+}
+
+func (lr *Rewriter) rewriteMetaRefresh(n *html.Node, baseDir string) int {
+	for i, attr := range n.Attr {
+		if attr.Key == "content" {
+			content := attr.Val
+			idx := strings.Index(strings.ToLower(content), "url=")
+			if idx == -1 {
+				return 0
+			}
+			urlStr := strings.TrimSpace(content[idx+4:])
+			parsed, err := url.Parse(urlStr)
+			if err != nil {
+				return 0
+			}
+			resolved := lr.baseURL.ResolveReference(parsed)
+			lr.visitedMu.RLock()
+			localPath, exists := lr.visited[resolved.String()]
+			lr.visitedMu.RUnlock()
+			if exists {
+				relPath, err := filepath.Rel(baseDir, localPath)
+				if err != nil {
+					relPath = localPath
+				}
+				n.Attr[i].Val = content[:idx+4] + filepath.ToSlash(relPath)
+				return 1
+			}
+			return 0
+		}
+	}
+	return 0
+}
+
+func (lr *Rewriter) rewriteAttr(n *html.Node, attrName, baseDir string) int {
+	for i, attr := range n.Attr {
+		if attr.Key != attrName {
+			continue
+		}
+		value := attr.Val
+		if strings.HasPrefix(value, "#") ||
+			strings.HasPrefix(value, "javascript:") ||
+			strings.HasPrefix(value, "mailto:") ||
+			strings.HasPrefix(value, "tel:") ||
+			strings.HasPrefix(value, "data:") ||
+			strings.HasPrefix(value, "about:") {
+			return 0
+		}
+		parsed, err := url.Parse(value)
+		if err != nil {
+			return 0
+		}
+		resolved := lr.baseURL.ResolveReference(parsed)
+		lr.visitedMu.RLock()
+		localPath, exists := lr.visited[resolved.String()]
+		lr.visitedMu.RUnlock()
+		if !exists {
+			return 0
+		}
+		relPath, err := filepath.Rel(baseDir, localPath)
+		if err != nil {
+			relPath = localPath
+		}
+		n.Attr[i].Val = filepath.ToSlash(relPath)
+		return 1
+	}
+	return 0
+}