add patch google analytics response modifier

proxychain/responsemodifers/patch_google_analytics.go

@@ -0,0 +1,33 @@
+package responsemodifers
+
+import (
+	_ "embed"
+	"io"
+	"ladder/proxychain"
+	"strings"
+)
+
+//go:embed patch_google_analytics.js
+var gaPatch string
+
+// PatchGoogleAnalytics replaces any request to google analytics with a no-op stub function.
+// Some sites will not display content until GA is loaded, so we fake one instead.
+// Credit to Raymond Hill @ github.com/gorhill/uBlock
+func PatchGoogleAnalytics() proxychain.ResponseModification {
+	return func(chain *proxychain.ProxyChain) error {
+
+		// preflight check
+		isGADomain := chain.Request.URL.Host == "www.google-analytics.com" || chain.Request.URL.Host == "google-analytics.com"
+		isGAPath := strings.HasSuffix(chain.Request.URL.Path, "analytics.js")
+		if !(isGADomain || isGAPath) {
+			return nil
+		}
+
+		// send modified js payload to client containing
+		// stub functions from patch_google_analytics.js
+		gaPatchReader := io.NopCloser(strings.NewReader(gaPatch))
+		chain.Response.Body = gaPatchReader
+		chain.Context.Set("content-type", "text/javascript")
+		return nil
+	}
+}