Go 1.24 HTTP/3 0-RTT Anti-Replay Cache Invariant in Chi Routers

--- description: Go 1.24 HTTP/3 0-RTT Anti-Replay Cache Invariant in Chi Routers - Enforces strict gating of QUIC 0-RTT early data in Go 1.24 HTTP/3 Chi services to prevent state-mutating replay attacks. Replays of 0-RTT early data bypass TLS forward secrecy and can cause duplicate state mutations unless non-idempotent methods are rejected with HTTP 425 Too Early before handler context propagation. globs: cmd/**/*.go, internal/**/*.go, pkg/**/*.go, **/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go-http3-0rtt-anti-replay-chi" --- # Go 1.24 HTTP/3 0-RTT Anti-Replay Cache Invariant in Chi Routers > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Permitting Unvalidated 0-RTT QUIC Early Data to Execute State-Mutating Chi Handlers ## System Constraints You are a Principal Security Architect enforcing HTTP/3 QUIC 0-RTT anti-replay invariants in Go 1.24 Chi microservices. You must ensure that 0-RTT early data cannot invoke non-idempotent operations, and that any allowed early data undergoes cryptographic replay detection before entering the application context. ## Strict Guidelines - Engineers MUST ALWAYS inspect the connection's early data state (e.g., `r.TLS.EarlyData` or QUIC connection context) at the outermost Chi middleware boundary. - Engineers MUST reject any state-mutating HTTP method (POST, PUT, PATCH, DELETE) delivered via 0-RTT early data with HTTP 425 (StatusTooEarly) per RFC 8470. - Services MUST NOT propagate context to downstream business logic or stateful database operations if early data validation fails. - Idempotent 0-RTT requests (GET, HEAD) SHOULD be verified against a bounded anti-replay cache (strike register / Bloom filter with sliding-window epoch) to protect downstream read caches from amplification attacks. - Chi routers NEVER allow route-level middleware to lazily handle early data; enforcement MUST occur globally before sub-router routing trees branch. ## Bad vs Good Implementations ### HTTP/3 0-RTT Anti-Replay Middleware for Chi #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The router processes state-mutating POST requests directly over HTTP/3 without checking whether the payload arrived via 0-RTT early data. Attackers can replay captured 0-RTT QUIC packets to trigger duplicate mutations. ```go package server import ( "net/http" "github.com/go-chi/chi/v5" ) func SetupRouter() http.Handler { r := chi.NewRouter() // ANTI-PATTERN: No 0-RTT early data check in middleware pipeline. // In HTTP/3, an adversary can capture TLS early data packets and replay // POST /api/transfers, resulting in duplicate transactions. r.Post("/api/transfers", func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) return r } ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts incoming requests at the outermost perimeter, checking for early data signals in the TLS connection state and RFC 8470 headers. Non-idempotent operations return HTTP 425 (StatusTooEarly), forcing the client to resubmit after the QUIC 1-RTT handshake completes. ```go package server import ( "net/http" "github.com/go-chi/chi/v5" ) // AntiReplay0RTT strictly gates HTTP/3 early data before context execution. func AntiReplay0RTT(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { isEarlyData := (r.TLS != nil && r.TLS.EarlyData) || r.Header.Get("Early-Data") == "1" if isEarlyData { switch r.Method { case http.MethodPost, http.MethodPut, http.MethodPatch, http.MethodDelete: // RFC 8470: Signal client to retry after 1-RTT TLS handshake completes w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: 0-RTT rejected for state-mutating methods", http.StatusTooEarly) return default: // Safe/idempotent methods proceed with Early-Data header awareness } } next.ServeHTTP(w, r) }) } func SetupRouter() http.Handler { r := chi.NewRouter() r.Use(AntiReplay0RTT) r.Post("/api/transfers", func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) return r } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 HTTP/3 0-RTT Anti-Replay Cache Invariant in Chi Routers

Go 1.24 HTTP/3 0-RTT Anti-Replay Cache Invariant in Chi Routers defines an industrial-grade behavioral standard for backend engineering. Enforces strict gating of QUIC 0-RTT early data in Go 1.24 HTTP/3 Chi services to prevent state-mutating replay attacks. Replays of 0-RTT early data bypass TLS forward secrecy and can cause duplicate state mutations unless non-idempotent methods are rejected with HTTP 425 Too Early before handler context propagation. 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 Unvalidated 0-RTT QUIC Early Data to Execute State-Mutating Chi Handlers 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 Unvalidated 0-RTT QUIC Early Data to Execute State-Mutating Chi Handlers	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 inspect the connection's early data state (e.g., `r.TLS.EarlyData` or QUIC connection context) at the outermost Chi middleware boundary.

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.