Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement

--- description: Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement - Mandates strict rejection or deterministic idempotency caching of QUIC 0-RTT early-data requests across distributed Go Chi edge gateways. Non-safe HTTP methods delivered via 0-RTT without cryptographically validated idempotency tokens must return HTTP 425 (Too Early) to force handshake completion. Ephemeral distributed Bloom filters must deduplicate concurrent and replayed early requests within the TLS ticket validity window. globs: **/middleware/**/*.go, **/router/**/*.go, **/gateway/**/*.go, cmd/gateway/**/*.go, pkg/transport/http3/**/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go-chi-http3-0rtt-anti-replay" --- # Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Permitting Non-Idempotent Mutations in Unverified QUIC 0-RTT Early Data Handshakes ## System Constraints You are a Principal Engineer enforcing Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement. Mandate invariants that block state-mutating replay attacks across QUIC early-data streams using distributed ephemeral bloom filters, RFC 8470 compliance, and HTTP 425 fallback semantics. ## Strict Guidelines - Services MUST inspect HTTP/3 early-data signals (RFC 8470 'Early-Data: 1' or TLS ConnectionState EarlyData) before routing requests to mutating handlers. - Engineers MUST NOT allow non-safe HTTP methods (POST, PUT, PATCH, DELETE) to execute inside 0-RTT early data unless accompanied by a verified Idempotency-Key and validated against the distributed ephemeral bloom filter. - Middleware MUST return HTTP 425 (Too Early) immediately if an early-data mutating request lacks a valid Idempotency-Key or if the anti-replay bloom filter indicates potential duplication. - The distributed ephemeral bloom filter MUST have a sliding retention window strictly bounded by the TLS session ticket lifetime (maximum early-data acceptance window). - Services MUST record successfully admitted 0-RTT idempotency keys in the distributed Bloom filter atomically before dispatching down the Chi middleware pipeline. ## Bad vs Good Implementations ### Vulnerable Mutating Route in 0-RTT Early Data vs RFC 8470 Anti-Replay Filter #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The handler does not inspect whether the request arrived via 0-RTT Early Data (RFC 8470). Network adversaries can capture the initial QUIC 0-RTT flight and replay it before the TLS session ticket expires, causing duplicate executions of state-mutating database operations. ```go package middleware import ( "net/http" "github.com/go-chi/chi/v5" ) // Flaw: Blindly passes HTTP/3 0-RTT early-data requests through to // mutating handlers, allowing packet replay attacks via QUIC handshakes. func UnsafeHTTP3Router() http.Handler { r := chi.NewRouter() r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { // If client used QUIC 0-RTT, an on-path attacker can replay this request // multiple times, causing duplicate financial transactions. executeFundsTransfer(r.Context(), r.Body) w.WriteHeader(http.StatusOK) }) return r } ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts early data via RFC 8470 headers. Non-safe HTTP methods without an Idempotency-Key or those detected as potentially replayed by the distributed Bloom filter are halted immediately with HTTP 425 (Too Early), instructing QUIC clients to retransmit only after the TLS 1.3 1-RTT handshake completes. ```go package middleware import ( "context" "net/http" "github.com/go-chi/chi/v5" ) type DistributedBloomFilter interface { TestAndAdd(ctx context.Context, key string) (alreadyExists bool, err error) } // HTTP3AntiReplayMiddleware enforces RFC 8470 safety and ephemeral bloom filter idempotency. func HTTP3AntiReplayMiddleware(bloom DistributedBloomFilter) func(next http.Handler) http.Handler { return func(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { isEarlyData := r.Header.Get("Early-Data") == "1" isSafeMethod := r.Method == http.MethodGet || r.Method == http.MethodHead || r.Method == http.MethodOptions if !isEarlyData { next.ServeHTTP(w, r) return } // Invariant: Non-safe methods in early data require an Idempotency-Key and replay verification if !isSafeMethod { idempotencyKey := r.Header.Get("Idempotency-Key") if idempotencyKey == "" { // Force client to retry after 1-RTT handshake completes w.Header().Set("Retry-After", "0") w.WriteHeader(http.StatusTooEarly) return } exists, err := bloom.TestAndAdd(r.Context(), idempotencyKey) if err != nil || exists { w.Header().Set("Retry-After", "0") w.WriteHeader(http.StatusTooEarly) return } } next.ServeHTTP(w, r) }) } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement

Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Idempotency Enforcement defines an industrial-grade behavioral standard for backend engineering. Mandates strict rejection or deterministic idempotency caching of QUIC 0-RTT early-data requests across distributed Go Chi edge gateways. Non-safe HTTP methods delivered via 0-RTT without cryptographically validated idempotency tokens must return HTTP 425 (Too Early) to force handshake completion. Ephemeral distributed Bloom filters must deduplicate concurrent and replayed early requests within the TLS ticket validity window. 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 Mutations in Unverified QUIC 0-RTT Early Data Handshakes 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 Mutations in Unverified QUIC 0-RTT Early Data Handshakes	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 HTTP/3 early-data signals (RFC 8470 'Early-Data

Services MUST inspect HTTP/3 early-data signals (RFC 8470 'Early-Data: 1' or TLS ConnectionState EarlyData) before routing requests to mutating 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.