Go Chi HTTP/3 Early-Data 0-RTT Anti-Replay Guardrail

--- description: Go Chi HTTP/3 Early-Data 0-RTT Anti-Replay Guardrail - Protects state-mutating HTTP endpoints against TLS 1.3 and QUIC HTTP/3 0-RTT early data replay attacks by enforcing RFC 8470 compliance. Mandates edge multiplexer middleware in Go Chi to reject non-idempotent early-data requests with HTTP 425 Too Early or validate them against a distributed single-use replay cache. 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-http3-early-data-anti-replay-go-chi-http-3-ea-558" --- # Go Chi HTTP/3 Early-Data 0-RTT Anti-Replay Guardrail > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Executing state-mutating operations over unvalidated 0-RTT QUIC/TLS early data without replay gating ## System Constraints You are a Principal Security Architect enforcing zero-trust HTTP/3 and TLS 1.3 early-data invariants in Go Chi services. 0-RTT early data is vulnerable to packet replay by passive-active on-path network adversaries. You must mandate strict adherence to RFC 8470: state-mutating requests (POST, PUT, DELETE, PATCH) arriving via early data MUST be rejected immediately with HTTP 425 (StatusTooEarly) to force client 1-RTT re-transmission, or gated behind an atomic, distributed single-use replay cache. Never trust transport-layer replay protection alone. ## Strict Guidelines - Services MUST inspect the 'Early-Data' header (RFC 8470) and QUIC/TLS connection state at the edge Go Chi middleware layer before invoking application handlers. - Engineers MUST ALWAYS reject non-idempotent HTTP methods (POST, PUT, DELETE, PATCH) with HTTP 425 StatusTooEarly when received in 0-RTT Early-Data. - Services MUST declare 'Early-Data' in response 'Vary' headers whenever routing or responses depend on early-data evaluation. - Engineers MUST NOT allow financial transactions, authentication state updates, credential rotations, or mutating write operations to execute within 0-RTT early data. - Code SHOULD enforce an atomic distributed replay-cache (e.g., Redis SETNX or sliding bloom filter with TLS cipher ticket age validation) if idempotent methods carrying mutation side-effects must be processed in 0-RTT. - Components NEVER blindly trust proxy-forwarded early-data headers without cryptographically verifying the upstream reverse-proxy connection signature or mTLS peer identity. ## Bad vs Good Implementations ### RFC 8470 Anti-Replay Chi Middleware for HTTP/3 0-RTT #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: State-mutating HTTP methods (POST, DELETE) are exposed directly over QUIC/TLS 0-RTT early data without inspecting the 'Early-Data' header or TLS connection state. Replayed 0-RTT packets will cause duplicate database writes and financial transactions. ```go package server import ( "net/http" "github.com/go-chi/chi/v5" ) func MountRoutes(r *chi.Mux) { // VULNERABLE: Endpoints process 0-RTT early data without validation. // Adversaries can capture and replay the QUIC Initial/0-RTT frames, // causing duplicate billing charges or multiple resource allocations. r.Post("/api/v1/payments", func(w http.ResponseWriter, r *http.Request) { ProcessPayment(w, r) }) r.Delete("/api/v1/resource/{id}", func(w http.ResponseWriter, r *http.Request) { DeleteResource(w, r) }) } func ProcessPayment(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusOK) } func DeleteResource(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusNoContent) } ``` #### Production Standard (Correct) > **Standard**: The AntiReplayGuardrail middleware intercepts early data flagged by RFC 8470 headers or edge proxies. If an unsafe method (POST, DELETE, PUT, PATCH) is sent in early data, it immediately responds with HTTP 425 StatusTooEarly, forcing the client to retransmit after the full handshake completes. It also sets the required Vary header. ```go package server import ( "net/http" "github.com/go-chi/chi/v5" ) // AntiReplayGuardrail enforces RFC 8470 early-data protection across HTTP/3 and TLS 1.3. func AntiReplayGuardrail(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { // Safe, idempotent methods according to RFC 7231 are permitted in 0-RTT isSafeMethod := r.Method == http.MethodGet || r.Method == http.MethodHead || r.Method == http.MethodOptions // Check RFC 8470 Early-Data header signaled by QUIC/HTTP3 reverse proxies or TLS terminates if r.Header.Get("Early-Data") == "1" { if !isSafeMethod { // Reject state-mutating requests to force client handshake completion (1-RTT) w.Header().Set("Vary", "Early-Data") http.Error(w, "Too Early: 0-RTT replay protection triggered", http.StatusTooEarly) return } w.Header().Set("Vary", "Early-Data") } next.ServeHTTP(w, r) }) } func MountRoutes(r *chi.Mux) { r.Use(AntiReplayGuardrail) r.Post("/api/v1/payments", func(w http.ResponseWriter, r *http.Request) { ProcessPayment(w, r) }) r.Delete("/api/v1/resource/{id}", func(w http.ResponseWriter, r *http.Request) { DeleteResource(w, r) }) } func ProcessPayment(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusOK) } func DeleteResource(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusNoContent) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go Chi HTTP/3 Early-Data 0-RTT Anti-Replay Guardrail

Go Chi HTTP/3 Early-Data 0-RTT Anti-Replay Guardrail defines an industrial-grade behavioral standard for backend engineering. Protects state-mutating HTTP endpoints against TLS 1.3 and QUIC HTTP/3 0-RTT early data replay attacks by enforcing RFC 8470 compliance. Mandates edge multiplexer middleware in Go Chi to reject non-idempotent early-data requests with HTTP 425 Too Early or validate them against a distributed single-use replay cache. 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: Executing state-mutating operations over unvalidated 0-RTT QUIC/TLS early data without replay gating 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	Executing state-mutating operations over unvalidated 0-RTT QUIC/TLS early data without replay gating	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:

Services MUST inspect the 'Early-Data' header (RFC 8470) and QUIC/TLS connection state at the edge Go Chi middleware layer before invoking application handlers.

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.