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

--- description: Go 1.24 HTTP/3 0-RTT Anti-Replay Idempotency Boundary Enforcement - RFC 8470 and RFC 9114 mandate that TLS 1.3 and QUIC 0-RTT (Early Data) frames are susceptible to passive network replay attacks. In Go 1.24 HTTP/3 edge gateways and services, handlers must enforce an absolute boundary invariant that forbids state-mutating HTTP methods within early data frames, immediately rejecting unconfirmed operations with HTTP 425 (Too Early) or gating them behind non-replayable distributed token leases. globs: **/*.go, **/gateway/**/*.go, **/middleware/**/*.go, **/transport/**/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go124-http3-zero-rtt-anti-replay-idempotency" --- # Go 1.24 HTTP/3 0-RTT Anti-Replay Idempotency Boundary Enforcement > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Processing Mutating HTTP Requests Inside Unconfirmed 0-RTT Early Data Frames ## System Constraints You are a Principal Security and Infrastructure Architect enforcing Go 1.24 HTTP/3 0-RTT anti-replay boundaries. Reject any implementation that allows state-mutating verbs (POST, PUT, PATCH, DELETE) or non-idempotent operations to execute within QUIC 0-RTT early data streams without explicit handshake completion checks or deterministic replay verification. ## Strict Guidelines - Services MUST ALWAYS inspect the TLS connection state and HTTP early data indicators (e.g., r.TLS.DidResume with EarlyData flag or the 'Early-Data: 1' header) before dispatching requests to application handlers. - Handlers MUST immediately terminate unsafe or non-idempotent HTTP methods (POST, PUT, PATCH, DELETE) received via 0-RTT with HTTP status 425 (StatusTooEarly) to trigger automatic client replay over the validated 1-RTT connection. - Engineers MUST NOT disable anti-replay mechanisms or blindly trust idempotency keys present within 0-RTT frames without a cryptographically bound distributed anti-replay ledger (e.g., sliding-window Redis/Aerospike filter). - Gateway middleware SHOULD populate the 'Early-Data' header forwarding state to downstream internal services, explicitly demarcating whether the packet arrived before the cryptographic handshake finalized. - Components NEVER execute side-effecting database writes, message bus publishing, or financial transactions on requests tagged as 0-RTT early data. ## Bad vs Good Implementations ### HTTP/3 0-RTT Anti-Replay Middleware #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The handler blindly accepts and processes a POST request over HTTP/3 without verifying whether the request was transmitted in 0-RTT early data. Attackers can replay the QUIC Initial and 0-RTT packets across distributed edge nodes to duplicate operations. ```go package gateway import ( "net/http" ) // Bad: Blindly executes mutating requests received during 0-RTT QUIC handshake. // An adversary can capture and replay 0-RTT UDP packets, executing double transfers or duplicate writes. func InsecureOrderHandler(w http.ResponseWriter, r *http.Request) { if r.Method == http.MethodPost { // Flaw: Mutating action executed without checking if request was received in early data processOrder(r.Context(), r.Body) w.WriteHeader(http.StatusCreated) } } func processOrder(ctx interface{}, body interface{}) {} ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts unconfirmed 0-RTT frames by inspecting connection handshake state and the 'Early-Data' signal. Any state-mutating method is halted with HTTP 425 (StatusTooEarly), forcing the client to resend the payload over a confirmed 1-RTT connection while preserving total idempotency. ```go package gateway import ( "crypto/tls" "net/http" "strings" ) // AntiReplayMiddleware isolates 0-RTT Early Data from state mutation. // Complies with RFC 8470 and RFC 9114 for Go 1.24 / QUIC HTTP/3 servers. func AntiReplayMiddleware(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { isEarlyData := r.Header.Get("Early-Data") == "1" if r.TLS != nil && !r.TLS.HandshakeComplete { isEarlyData = true } if isEarlyData { // Safe/idempotent methods can proceed if marked safe, otherwise reject immediately switch strings.ToUpper(r.Method) { case http.MethodGet, http.MethodHead, http.MethodOptions: // Allowed: RFC 9114 safe methods are permissible in early data w.Header().Set("Early-Data", "1") default: // Invariant: Non-idempotent operations must be rejected with 425 Too Early // Instructs conformant HTTP/3 clients to retry post-handshake over 1-RTT w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Mutating operation rejected in 0-RTT frame", http.StatusTooEarly) return } } next.ServeHTTP(w, r) }) } ```

Architectural Specification & Invariant Rationale

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

Go 1.24 HTTP/3 0-RTT Anti-Replay Idempotency Boundary Enforcement defines an industrial-grade behavioral standard for backend engineering. RFC 8470 and RFC 9114 mandate that TLS 1.3 and QUIC 0-RTT (Early Data) frames are susceptible to passive network replay attacks. In Go 1.24 HTTP/3 edge gateways and services, handlers must enforce an absolute boundary invariant that forbids state-mutating HTTP methods within early data frames, immediately rejecting unconfirmed operations with HTTP 425 (Too Early) or gating them behind non-replayable distributed token leases. 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: Processing Mutating HTTP Requests Inside Unconfirmed 0-RTT Early Data Frames 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	Processing Mutating HTTP Requests Inside Unconfirmed 0-RTT Early Data Frames	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 ALWAYS inspect the TLS connection state and HTTP early data indicators (e.g., r.TLS.DidResume with EarlyData flag or the 'Early-Data

Services MUST ALWAYS inspect the TLS connection state and HTTP early data indicators (e.g., r.TLS.DidResume with EarlyData flag or the 'Early-Data: 1' header) before dispatching requests to application 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.