Go Chi RFC 8470 TLS 0-RTT Early-Data Anti-Replay Guardrail

--- description: Go Chi RFC 8470 TLS 0-RTT Early-Data Anti-Replay Guardrail - Enforces RFC 8470 compliance on Go Chi routers by strictly fencing TLS 1.3 and QUIC 0-RTT early data against non-safe HTTP methods. Prevents replay-based state corruption and duplicate transactions on distributed HTTP/3 endpoints by deterministically terminating early requests with HTTP 425 Too Early. globs: **/*.go, cmd/**/*.go, internal/**/*.go, pkg/**/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go-chi-rfc-8470-early-data-anti-replay" --- # Go Chi RFC 8470 TLS 0-RTT Early-Data Anti-Replay Guardrail > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Permitting Non-Idempotent HTTP/3 0-RTT Early Data Execution Without RFC 8470 Fencing ## System Constraints You are a Principal Backend Security Architect enforcing the Go Chi RFC 8470 Early-Data Anti-Replay Invariant. TLS 1.3 and QUIC 0-RTT early data does not provide replay protection across distributed nodes. You must ensure that any non-safe HTTP method (POST, PUT, PATCH, DELETE) received within an early-data context is immediately rejected with HTTP 425 (Too Early) before touching application state or handler pipelines. ## Strict Guidelines - Engineers MUST ALWAYS enforce early-data rejection middleware at the root or mutation-specific subrouters in Go Chi before any business logic handlers execute. - Engineers MUST NOT allow non-idempotent or non-safe HTTP methods (POST, PUT, PATCH, DELETE) to execute when the 'Early-Data' header equals '1' or when the underlying TLS connection state indicates early data. - Services MUST emit an HTTP 425 (Too Early) status code and include a 'Retry-After: 0' header when rejecting early data under RFC 8470 specifications. - Components NEVER rely on application-level deduplication caches alone for replay defense under 0-RTT; transport fencing MUST happen before request body consumption or database transactions. - Edge proxies and reverse proxies MUST be configured to forward the standard 'Early-Data: 1' header to upstream Go Chi servers if the proxy terminated 0-RTT QUIC/TLS handshakes. ## Bad vs Good Implementations ### RFC 8470 Early Data Replay Protection in Go Chi #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The handler registers state-altering POST routes directly without evaluating early-data markers. Under HTTP/3 or TLS 1.3 0-RTT, network adversaries can replay early flights to repeat operations with side effects. ```go package transport import ( "net/http" "github.com/go-chi/chi/v5" ) func RegisterRoutes(r *chi.Mux) { // VULNERABLE: Lacks RFC 8470 0-RTT fencing. // An adversary intercepting initial HTTP/3 QUIC 0-RTT flight packets // can replay duplicate transfer requests across edge instances. r.Post("/api/v1/settlements", func(w http.ResponseWriter, r *http.Request) { executeFundsTransfer(r.Context(), r.Body) w.WriteHeader(http.StatusAccepted) }) } ``` #### Production Standard (Correct) > **Standard**: Middleware intercepts the request before body consumption or routing execution. If 'Early-Data: 1' is present on non-safe verbs, it aborts immediately with HTTP 425 and instructs the client to retry over a finalized 1-RTT connection. ```go package transport import ( "net/http" "github.com/go-chi/chi/v5" ) // RFC8470AntiReplay returns a Chi middleware enforcing RFC 8470 early-data invariant. func RFC8470AntiReplay(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { if r.Header.Get("Early-Data") == "1" { switch r.Method { case http.MethodPost, http.MethodPut, http.MethodPatch, http.MethodDelete: w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: 0-RTT early data disallowed for non-safe methods", http.StatusTooEarly) return } } next.ServeHTTP(w, r) }) } func RegisterRoutes(r *chi.Mux) { r.Route("/api/v1", func(api chi.Router) { api.Use(RFC8470AntiReplay) api.Post("/settlements", func(w http.ResponseWriter, r *http.Request) { executeFundsTransfer(r.Context(), r.Body) w.WriteHeader(http.StatusAccepted) }) }) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go Chi RFC 8470 TLS 0-RTT Early-Data Anti-Replay Guardrail

Go Chi RFC 8470 TLS 0-RTT Early-Data Anti-Replay Guardrail defines an industrial-grade behavioral standard for backend engineering. Enforces RFC 8470 compliance on Go Chi routers by strictly fencing TLS 1.3 and QUIC 0-RTT early data against non-safe HTTP methods. Prevents replay-based state corruption and duplicate transactions on distributed HTTP/3 endpoints by deterministically terminating early requests with HTTP 425 Too Early. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Permitting Non-Idempotent HTTP/3 0-RTT Early Data Execution Without RFC 8470 Fencing Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Permitting Non-Idempotent HTTP/3 0-RTT Early Data Execution Without RFC 8470 Fencing	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS enforce early-data rejection middleware at the root or mutation-specific subrouters in Go Chi before any business logic handlers execute.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.