add modify incoming scripts with regex modifier

proxychain/responsemodifiers/modify_incoming_scripts_with_regex.go

@@ -0,0 +1,53 @@
+package responsemodifiers
+
+import (
+	"bytes"
+	"io"
+	"regexp"
+	"strings"
+
+	"github.com/everywall/ladder/proxychain"
+)
+
+// ModifyIncomingScriptsWithRegex modifies all incoming javascript (application/javascript and inline <script> in text/html) using a regex match and replacement.
+func ModifyIncomingScriptsWithRegex(matchRegex string, replacement string) proxychain.ResponseModification {
+	return func(chain *proxychain.ProxyChain) error {
+		path := chain.Request.URL.Path
+		ct := chain.Response.Header.Get("content-type")
+		isJavascript := strings.HasSuffix(path, ".js") || ct == "text/javascript" || ct == "application/javascript"
+		isHTML := strings.HasSuffix(chain.Request.URL.Path, ".html") || ct == "text/html"
+
+		switch {
+		case isJavascript:
+			rBody, err := modifyResponse(chain.Response.Body, matchRegex, replacement)
+			if err != nil {
+				return err
+			}
+			chain.Response.Body = rBody
+		case isHTML:
+		default:
+			return nil
+		}
+		return nil
+	}
+}
+
+func modifyResponse(body io.ReadCloser, matchRegex, replacement string) (io.ReadCloser, error) {
+	content, err := io.ReadAll(body)
+	if err != nil {
+		return nil, err
+	}
+
+	re, err := regexp.Compile(matchRegex)
+	if err != nil {
+		return nil, err
+	}
+	err = body.Close()
+	if err != nil {
+		return body, err
+	}
+
+	modifiedContent := re.ReplaceAll(content, []byte(replacement))
+
+	return io.NopCloser(bytes.NewReader(modifiedContent)), nil
+}