Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Guardrail for Mutating Endpoints

--- description: Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Guardrail for Mutating Endpoints - Enforces strict rejection of non-idempotent HTTP methods received via HTTP/3 0-RTT early data handshakes using HTTP 425 (Too Early) per RFC 8470. Prevents network attackers from executing packet replay attacks against state-mutating handlers before the QUIC/TLS handshake completes. 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-zero-rtt-anti-replay-guardrail-go-1-24-chi-http-359" --- # Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Guardrail for Mutating Endpoints > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Executing State-Mutating Chi Handlers via Replayable HTTP/3 0-RTT Early Data ## System Constraints You are a Principal Systems and Security Architect enforcing HTTP/3 0-RTT anti-replay boundaries in Go 1.24 services using the Chi router. Mandate that mutating HTTP methods (POST, PUT, PATCH, DELETE) executed across QUIC 0-RTT early data handshakes are rejected with status 425 (Too Early) or gated strictly behind replay-safe middleware. ## Strict Guidelines - Services MUST inspect the 'Early-Data' header (RFC 8470) and QUIC early data context before processing non-safe HTTP methods (POST, PUT, PATCH, DELETE). - Middleware MUST respond with HTTP 425 (StatusTooEarly) whenever an early-data request targets a non-idempotent endpoint, allowing compliant clients to retry on 1-RTT. - Engineers MUST NOT disable TLS 0-RTT replay protection flags or assume transport-layer deduplication protects application-level state. - Chi route subtrees containing transactional mutations MUST be wrapped with an Anti-Replay / Early-Data rejection middleware. - Engineers MUST ensure safe, read-only methods (GET, HEAD, OPTIONS) accepted in 0-RTT remain strictly idempotent and free of stateful side-effects. ## Bad vs Good Implementations ### Chi HTTP/3 0-RTT Anti-Replay Middleware Implementation #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The POST handler accepts requests transported via HTTP/3 0-RTT early data without checking the 'Early-Data' header or QUIC early data status. An attacker replaying 0-RTT packets can trigger repeated financial transactions without possessing the client's current session keys. ```go package main import ( "net/http" "github.com/go-chi/chi/v5" ) func main() { r := chi.NewRouter() // VULNERABILITY: Non-idempotent mutation handler directly exposed to HTTP/3. // A passive network attacker can capture the 0-RTT QUIC Initial/0-RTT packets // and replay them to execute duplicate fund transfers. r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { // State mutation executes without checking if request is early data w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) _ = http.ListenAndServeTLS(":443", "cert.pem", "key.pem", r) } ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts early-data requests indicated by RFC 8470. Non-idempotent methods are rejected with HTTP 425 (StatusTooEarly) and a 'Retry-After: 0' header, ensuring mutating state operations execute strictly after the TLS 1-RTT handshake is finalized. ```go package main import ( "net/http" "github.com/go-chi/chi/v5" ) // RejectEarlyDataForMutations enforces RFC 8470 anti-replay safety. func RejectEarlyDataForMutations(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { isEarlyData := r.Header.Get("Early-Data") == "1" // Safe/idempotent methods can proceed in 0-RTT; mutating methods must be rejected. if isEarlyData { switch r.Method { case http.MethodGet, http.MethodHead, http.MethodOptions: // Idempotent read requests are permissible in early data default: // Instruct client to resend after TLS 1-RTT handshake completes w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Non-idempotent method rejected in 0-RTT", http.StatusTooEarly) return } } next.ServeHTTP(w, r) }) } func main() { r := chi.NewRouter() r.Use(RejectEarlyDataForMutations) r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) _ = http.ListenAndServeTLS(":443", "cert.pem", "key.pem", r) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Guardrail for Mutating Endpoints

Go 1.24 Chi HTTP/3 0-RTT Anti-Replay Guardrail for Mutating Endpoints defines an industrial-grade behavioral standard for backend engineering. Enforces strict rejection of non-idempotent HTTP methods received via HTTP/3 0-RTT early data handshakes using HTTP 425 (Too Early) per RFC 8470. Prevents network attackers from executing packet replay attacks against state-mutating handlers before the QUIC/TLS handshake completes. 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 Chi Handlers via Replayable 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	Executing State-Mutating Chi Handlers via Replayable 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:

Services MUST inspect the 'Early-Data' header (RFC 8470) and QUIC early data context before processing non-safe HTTP methods (POST, PUT, PATCH, DELETE).

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.