refactor rewriters to modify html in single pass with multiple rewriters; improve html rewriter edge case handling

proxychain/responsemodifers/inject_script.go

@@ -0,0 +1,27 @@
+package responsemodifers
+
+import (
+	_ "embed"
+	"ladder/proxychain"
+	"ladder/proxychain/responsemodifers/rewriters"
+	"strings"
+)
+
+// InjectScript modifies HTTP responses
+// to execute javascript at a particular time.
+func InjectScript(js string, execTime rewriters.ScriptExecTime) proxychain.ResponseModification {
+	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
+		}
+
+		// the rewriting actually happens in chain.Execute() as the client is streaming the response body back
+		rr := rewriters.NewScriptInjectorRewriter(js, execTime)
+		// we just queue it up here
+		chain.AddHTMLTokenRewriter(rr)
+
+		return nil
+	}
+}