add subdomain url extractor; add 3p script blocker modifier

proxychain/responsemodifiers/block_third_party_scripts.go

@@ -0,0 +1,33 @@
+package responsemodifiers
+
+import (
+	_ "embed"
+	"fmt"
+	"strings"
+
+	"ladder/proxychain"
+	"ladder/proxychain/responsemodifiers/rewriters"
+)
+
+// BlockThirdPartyScripts rewrites HTML and injects JS to block all third party JS from loading.
+func BlockThirdPartyScripts() proxychain.ResponseModification {
+	// TODO: monkey patch fetch and XMLHttpRequest to firewall 3P JS as well.
+	return func(chain *proxychain.ProxyChain) error {
+		// don't add rewriter if it's not even html
+		ct := chain.Response.Header.Get("content-type")
+		if !strings.HasPrefix(ct, "text/html") {
+			return nil
+		}
+
+		// proxyURL is the URL of the ladder: http://localhost:8080 (ladder)
+		originalURI := chain.Context.Request().URI()
+		proxyURL := fmt.Sprintf("%s://%s", originalURI.Scheme(), originalURI.Host())
+
+		// replace http.Response.Body with a readcloser that wraps the original, modifying the html attributes
+		rr := rewriters.NewBlockThirdPartyScriptsRewriter(chain.Request.URL, proxyURL)
+		blockJSRewriter := rewriters.NewHTMLRewriter(chain.Response.Body, rr)
+		chain.Response.Body = blockJSRewriter
+
+		return nil
+	}
+}