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

--- description: Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Barrier - Enforces a strict idempotency and early data rejection barrier for HTTP/3 connections using Go and Chi. QUIC 0-RTT allows early application data frames to be sent prior to the completion of the 1-RTT cryptographic handshake, exposing state-mutating HTTP methods to network-level replay attacks. The guardrail guarantees that unsafe HTTP requests arriving in early data are intercepted and rejected with HTTP 425 (Too Early) or validated through an atomic, distributed replay cache. globs: **/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go-chi-quic-0rtt-anti-replay-idempotency" --- # Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Barrier > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Executing Non-Idempotent HTTP Handlers on Unvalidated 0-RTT QUIC Early Data ## System Constraints You are a Principal Security and Network Architect enforcing strict HTTP/3 QUIC 0-RTT anti-replay boundaries in Go applications utilizing the Chi router. You must reject or deflect any state-mutating requests received over early data channels lacking full 1-RTT cryptographic finality. Mandate invariant enforcement across middleware stacks, TLS configurations, and idempotency key layers. ## Strict Guidelines - Engineers MUST ALWAYS inspect the request TLS state or quic-go early data context to verify whether a request arrived via 0-RTT early data. - Engineers MUST NOT allow non-safe HTTP methods (POST, PUT, PATCH, DELETE) to execute over 0-RTT without an explicit, cryptographically bound anti-replay token validated against an atomic distributed store. - Services MUST emit HTTP status code 425 (Too Early) whenever an unsafe or non-idempotent request is received over early data, instructing the client to retransmit only after the full 1-RTT handshake completes. - Middleware MUST record and validate client-supplied Idempotency-Keys in a distributed Redis/Dragonfly cluster with atomic SETNX and finite lease windows before routing requests to handler pipelines. - Code MUST isolate safe idempotent read operations (GET, HEAD, OPTIONS) from mutating operations when configuring early data acceptance thresholds in quic-go/http3 listeners. ## Bad vs Good Implementations ### Chi Anti-Replay 0-RTT Barrier Middleware Implementation #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The HTTP POST route executes business logic without checking if the request was delivered via QUIC 0-RTT early data. In an active replay attack, an eavesdropper can replay recorded QUIC 0-RTT packets before TLS key establishment finishes, causing duplicate financial transactions. ```go package server import ( "net/http" "github.com/go-chi/chi/v5" ) func MountVulnerableRoutes(r chi.Router) { // ANTI-PATTERN: Mutating endpoint exposed directly over HTTP/3 with 0-RTT enabled // Attacker can duplicate the 0-RTT QUIC initial flight packets, triggering duplicate transfers r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { // State-changing operation executes immediately upon early data receipt w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) } ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts incoming requests to inspect the QUIC TLS EarlyData flag and HTTP Early-Data headers. If an unsafe mutating HTTP method arrives prior to handshake completion, it either fails fast with HTTP 425 (Too Early) forcing 1-RTT retransmission, or demands an atomic distributed idempotency token via Redis SETNX. ```go package server import ( "context" "net/http" "time" "github.com/go-chi/chi/v5" "github.com/quic-go/quic-go/http3" "github.com/redis/go-redis/v9" ) // AntiReplayBarrier prevents execution of unsafe methods in 0-RTT early data func AntiReplayBarrier(rdb *redis.Client) func(http.Handler) http.Handler { return func(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) { ctx := req.Context() // Check if request was received in 0-RTT early data isEarlyData := false if req.TLS != nil && req.TLS.EarlyData { isEarlyData = true } else if req.Header.Get("Early-Data") == "1" { isEarlyData = true } isSafeMethod := req.Method == http.MethodGet || req.Method == http.MethodHead || req.Method == http.MethodOptions if isEarlyData && !isSafeMethod { idempotencyKey := req.Header.Get("Idempotency-Key") if idempotencyKey == "" { // Invariant: Non-idempotent 0-RTT requests must fail with 425 Too Early w.Header().Set("Retry-After-Handshake", "1") http.Error(w, "Too Early: Retransmit over 1-RTT", http.StatusTooEarly) return } // Atomic lock to guarantee replay rejection lockKey := "0rtt:lock:" + idempotencyKey ok, err := rdb.SetNX(ctx, lockKey, "locked", 10*time.Minute).Result() if err != nil || !ok { http.Error(w, "Duplicate early data frame rejected", http.StatusTooEarly) return } } next.ServeHTTP(w, req) }) } } ```

Architectural Specification & Invariant Rationale

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

Go Chi HTTP/3 0-RTT Anti-Replay Idempotency Barrier defines an industrial-grade behavioral standard for backend engineering. Enforces a strict idempotency and early data rejection barrier for HTTP/3 connections using Go and Chi. QUIC 0-RTT allows early application data frames to be sent prior to the completion of the 1-RTT cryptographic handshake, exposing state-mutating HTTP methods to network-level replay attacks. The guardrail guarantees that unsafe HTTP requests arriving in early data are intercepted and rejected with HTTP 425 (Too Early) or validated through an atomic, distributed 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 Non-Idempotent HTTP Handlers on Unvalidated 0-RTT QUIC 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	Executing Non-Idempotent HTTP Handlers on Unvalidated 0-RTT QUIC 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 request TLS state or quic-go early data context to verify whether a request arrived via 0-RTT early data.

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.