Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard

--- description: Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard - Enforces deterministic anti-replay protection across HTTP/3 QUIC 0-RTT early-data handshakes in Go Chi routing topologies. Eliminates duplicate state mutations during volatile mobile edge reconnects by pairing RFC 8470 Early-Data validation with distributed atomic nonce reservations. 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-http3-0rtt-anti-replay-idempotency" --- # Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Blind Execution of State-Mutating Handshake Requests Over HTTP/3 0-RTT Early Data ## System Constraints You are a Principal Software Architect enforcing the Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard. Mandate that any state-mutating HTTP methods (POST, PUT, PATCH, DELETE) received with an 'Early-Data: 1' header or over QUIC 0-RTT handshakes strictly implement RFC 8470 validation and atomic distributed nonce fingerprinting. Never allow unverified mutation pipelines to process early data. ## Strict Guidelines - Engineers MUST ALWAYS inspect the 'Early-Data' header on state-mutating routes (POST, PUT, PATCH, DELETE) when serving HTTP/3 over QUIC. - Engineers MUST NOT allow non-idempotent mutations over 0-RTT without an explicit, cryptographically verifiable 'Idempotency-Key' and deterministic client fingerprint. - Code SHOULD return '425 Too Early' immediately if a mutating request arrives via 0-RTT without an idempotency key or if downstream replay validation cannot complete atomically. - Services MUST atomically claim idempotency fingerprints using a distributed lock-free primitive (e.g., Redis SET NX EX) before initiating business transactions. - Components NEVER execute raw database writes or external side-effects inside Chi handlers prior to early-data validation and nonce confirmation. ## Bad vs Good Implementations ### Chi Anti-Replay Middleware for QUIC 0-RTT Early Data #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Fails to inspect the 'Early-Data' header or enforce idempotency keys on QUIC early-data handshakes. State-mutating requests can be intercepted and replayed multiple times by an on-path attacker before the TLS 1.3 handshake completes. ```go package middleware import ( "net/http" ) // Flawed: Passes 0-RTT early-data directly to mutating handlers without replay checks. func NaiveEarlyDataHandler(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { // 0-RTT replay vulnerability: Attacker can retransmit TLS ClientHello and // duplicate credit deductions or order placements over QUIC early data. next.ServeHTTP(w, r) }) } ``` #### Production Standard (Correct) > **Standard**: Implements RFC 8470 early-data rejection via HTTP 425 (Too Early) when idempotency nonces are absent or duplicated. Employs atomic distributed key claims (SetNX) to ensure replayed QUIC packets cannot trigger duplicate mutations during connection handshakes. ```go package middleware import ( "context" "crypto/sha256" "encoding/hex" "fmt" "net/http" "time" "github.com/redis/go-redis/v9" ) type AntiReplay struct { rdb *redis.Client ttl time.Duration } func NewAntiReplay(rdb *redis.Client, ttl time.Duration) *AntiReplay { return &AntiReplay{rdb: rdb, ttl: ttl} } func (ar *AntiReplay) Middleware(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { isEarlyData := r.Header.Get("Early-Data") == "1" isMutating := r.Method == http.MethodPost || r.Method == http.MethodPut || r.Method == http.MethodPatch || r.Method == http.MethodDelete if !isEarlyData || !isMutating { next.ServeHTTP(w, r) return } idempotencyKey := r.Header.Get("Idempotency-Key") if idempotencyKey == "" { // RFC 8470: Reject unsafe 0-RTT requests lacking client idempotency guarantees. w.Header().Set("Retry-After", "1") http.Error(w, "Too Early: Idempotency-Key required for 0-RTT mutations", http.StatusTooEarly) return } // Create deterministic fingerprint over client token and request scope hash := sha256.New() hash.Write([]byte(fmt.Sprintf("%s:%s:%s", r.Method, r.URL.Path, idempotencyKey))) fingerprint := hex.EncodeToString(hash.Sum(nil)) redisKey := fmt.Sprintf("replay_guard:0rtt:%s", fingerprint) ctx, cancel := context.WithTimeout(r.Context(), 500*time.Millisecond) defer cancel() ok, err := ar.rdb.SetNX(ctx, redisKey, "claimed", ar.ttl).Result() if err != nil || !ok { // Nonce exists or cache unavailable; force client to re-send over 1-RTT. w.Header().Set("Retry-After", "1") http.Error(w, "Too Early: Potential 0-RTT replay detected", http.StatusTooEarly) return } next.ServeHTTP(w, r) }) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard

Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Standard defines an industrial-grade behavioral standard for backend engineering. Enforces deterministic anti-replay protection across HTTP/3 QUIC 0-RTT early-data handshakes in Go Chi routing topologies. Eliminates duplicate state mutations during volatile mobile edge reconnects by pairing RFC 8470 Early-Data validation with distributed atomic nonce reservations. 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: Blind Execution of State-Mutating Handshake Requests Over HTTP/3 0-RTT Early Data 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	Blind Execution of State-Mutating Handshake Requests Over HTTP/3 0-RTT Early Data	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 'Early-Data' header on state-mutating routes (POST, PUT, PATCH, DELETE) when serving HTTP/3 over QUIC.

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.