add subdomain url extractor; add 3p script blocker modifier

proxychain/responsemodifiers/rewriters/block_third_party_scripts.go

@@ -0,0 +1,69 @@
+package rewriters
+
+import (
+	_ "embed"
+	"fmt"
+	"log"
+	"net/url"
+	"strings"
+
+	"golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
+)
+
+// BlockThirdPartyScriptsRewriter implements HTMLTokenRewriter
+// and blocks 3rd party JS in script tags by replacing the src attribute value "blocked"
+type BlockThirdPartyScriptsRewriter struct {
+	baseURL  *url.URL
+	proxyURL string // ladder URL, not proxied site URL
+}
+
+// NewBlockThirdPartyScriptsRewriter creates a new instance of BlockThirdPartyScriptsRewriter.
+// This rewriter will strip out 3rd party JS URLs from script tags.
+func NewBlockThirdPartyScriptsRewriter(baseURL *url.URL, proxyURL string) *BlockThirdPartyScriptsRewriter {
+	return &BlockThirdPartyScriptsRewriter{
+		baseURL:  baseURL,
+		proxyURL: proxyURL,
+	}
+}
+
+func (r *BlockThirdPartyScriptsRewriter) ShouldModify(token *html.Token) bool {
+	if token.DataAtom != atom.Script {
+		return false
+	}
+
+	// check for 3p .js urls in html elements
+	for i := range token.Attr {
+		attr := token.Attr[i]
+		switch {
+		case attr.Key != "src":
+			continue
+		case strings.HasPrefix(attr.Val, "/"):
+			return false
+		case !strings.HasPrefix(attr.Val, "http"):
+			return false
+		case strings.HasPrefix(attr.Val, r.proxyURL):
+			return false
+		case strings.HasPrefix(attr.Val, fmt.Sprintf("%s://%s", r.baseURL.Scheme, r.baseURL.Hostname())):
+			return false
+		}
+	}
+
+	return true
+}
+
+func (r *BlockThirdPartyScriptsRewriter) ModifyToken(token *html.Token) (string, string) {
+	for i := range token.Attr {
+		attr := &token.Attr[i]
+		if attr.Key != "src" {
+			continue
+		}
+
+		if !strings.HasPrefix(attr.Val, "http") {
+			continue
+		}
+		log.Printf("INFO: blocked 3P js: '%s' on '%s'\n", attr.Val, r.baseURL.String())
+		attr.Key = "blocked"
+	}
+	return "", ""
+}