add patch tracker scripts response modifier

proxychain/responsemodifers/patch_tracker_scripts.go

@@ -0,0 +1,99 @@
+package responsemodifers
+
+import (
+	"embed"
+	"encoding/json"
+	"io"
+	"ladder/proxychain"
+	"log"
+	"regexp"
+)
+
+//go:embed vendor/ddg-tracker-surrogates/mapping.json
+var mappingJSON []byte
+
+//go:embed vendor/ddg-tracker-surrogates/surrogates/*
+var surrogateFS embed.FS
+
+var rules domainRules
+
+func init() {
+	err := json.Unmarshal([]byte(mappingJSON), &rules)
+	if err != nil {
+		log.Printf("[ERROR]: PatchTrackerScripts: failed to deserialize ladder/proxychain/responsemodifers/vendor/ddg-tracker-surrogates/mapping.json")
+	}
+}
+
+// mapping.json schema
+type rule struct {
+	RegexRule *regexp.Regexp `json:"regexRule"`
+	Surrogate string         `json:"surrogate"`
+	Action    string         `json:"action,omitempty"`
+}
+
+type domainRules map[string][]rule
+
+func (r *rule) UnmarshalJSON(data []byte) error {
+	type Tmp struct {
+		RegexRule string `json:"regexRule"`
+		Surrogate string `json:"surrogate"`
+		Action    string `json:"action,omitempty"`
+	}
+
+	var tmp Tmp
+	if err := json.Unmarshal(data, &tmp); err != nil {
+		return err
+	}
+
+	regex := regexp.MustCompile(tmp.RegexRule)
+
+	r.RegexRule = regex
+	r.Surrogate = tmp.Surrogate
+	r.Action = tmp.Action
+
+	return nil
+}
+
+// PatchTrackerScripts replaces any request to tracker scripts such as google analytics
+// with a no-op stub that mocks the API structure of the original scripts they replace.
+// Some pages depend on the existence of these structures for proper loading, so this may fix
+// some broken elements.
+// Surrogate script code borrowed from: DuckDuckGo Privacy Essentials browser extension for Firefox, Chrome. (Apache 2.0 license)
+func PatchTrackerScripts() proxychain.ResponseModification {
+
+	return func(chain *proxychain.ProxyChain) error {
+
+		// preflight checks
+		reqURL := chain.Request.URL.String()
+		isTracker := false
+
+		var surrogateScript io.ReadCloser
+		for domain, domainRules := range rules {
+			for _, rule := range domainRules {
+				if !rule.RegexRule.MatchString(reqURL) {
+					continue
+				}
+
+				// found tracker script, replacing response body with nop stub from
+				// ./vendor/ddg-tracker-surrogates/surrogates/{{rule.Surrogate}}
+				isTracker = true
+				script, err := surrogateFS.Open("vendor/ddg-tracker-surrogates/surrogates/" + rule.Surrogate)
+				if err != nil {
+					panic(err)
+				}
+				surrogateScript = io.NopCloser(script)
+				log.Printf("INFO: PatchTrackerScripts :: injecting surrogate for '%s' => 'surrogates/%s'\n", domain, rule.Surrogate)
+				break
+
+			}
+		}
+
+		if !isTracker {
+			return nil
+		}
+
+		chain.Response.Body = surrogateScript
+		chain.Context.Set("content-type", "text/javascript")
+		return nil
+	}
+}