Go 1.24 HTTP/3 0-RTT Distributed Anti-Replay Guardrail

--- description: Go 1.24 HTTP/3 0-RTT Distributed Anti-Replay Guardrail - Enforces strict 0-RTT (Early Data) validation across Go HTTP/3 services to eliminate replay attacks at the edge. Guarantees that state-altering methods are rejected immediately with HTTP 425 (Too Early) and idempotent early data routes validate cryptographically signed temporal tokens against a distributed sliding window. globs: **/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go124-http3-zero-rtt-anti-replay-invariant" --- # Go 1.24 HTTP/3 0-RTT Distributed Anti-Replay Guardrail > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Unchecked HTTP/3 0-RTT Early Data execution enabling distributed request replay and duplicate side-effects. ## System Constraints You are a Principal Software Architect enforcing Go 1.24 HTTP/3 0-RTT Anti-Replay invariants. In HTTP/3 over QUIC, 0-RTT early data allows clients to transmit requests before the cryptographic handshake finishes, exposing endpoints to packet replays across distributed edge nodes (RFC 8470). You must ensure: (1) Non-safe HTTP methods (POST, PUT, DELETE, PATCH) transported via 0-RTT are rejected with HTTP 425 Too Early; (2) Permitted idempotent 0-RTT routes strictly evaluate an authenticated temporal token; (3) Monotonic tokens are verified against a distributed cache (e.g., Redis via atomic SET NX with bounded TTL matching the maximum 0-RTT window); (4) Rejected early requests instruct proxies and clients to re-issue over a fully established TLS 1.3 session. ## Strict Guidelines - Engineers MUST ALWAYS inspect the 'Early-Data' header ('1') and underlying QUIC connection state to detect 0-RTT transmission. - Engineers MUST IMMEDIATELY reject non-idempotent HTTP methods (POST, PUT, PATCH, DELETE) arriving via 0-RTT with HTTP status code 425 (StatusTooEarly). - Services MUST validate temporal replay tokens (containing Unix timestamp, nonce, and HMAC) against a bounded drift window (default maximum +/- 10 seconds). - Middleware MUST record validated nonces in a distributed coordination store using atomic operations (e.g., Redis 'SET key val NX EX window') before executing route handlers. - Handlers MUST NEVER execute side-effects or state transitions based on unvalidated 0-RTT payloads. - Reverse proxy configurations MUST forward 'Early-Data' headers accurately and propagate HTTP 425 upstream to force TLS handshake completion before retry. ## Bad vs Good Implementations ### HTTP/3 0-RTT Early Data Anti-Replay Middleware #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The middleware accepts Early Data blindly without verifying HTTP method safety, lacks temporal token validation, and fails to check a distributed nonce window. An attacker can replay 0-RTT frames across multiple edge nodes to duplicate operations. ```go package middleware import ( "net/http" ) // Flawed: blind processing of 0-RTT early data permits replay attacks across proxies func HTTP3EarlyDataMiddleware(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { // Anti-pattern: Allows POST/PUT requests in early data with no replay validation if r.Header.Get("Early-Data") == "1" { // Attacker can capture and replay this QUIC 0-RTT packet indefinitely next.ServeHTTP(w, r) return } next.ServeHTTP(w, r) }) } ``` #### Production Standard (Correct) > **Standard**: Implements full RFC 8470 anti-replay invariants: (1) Rejects non-idempotent methods with HTTP 425; (2) Enforces bounded temporal validity on the early data token; (3) Validates HMAC integrity; (4) Atomically claims the nonce in distributed storage using SetNX with safe TTL to defeat cross-proxy replays. ```go package middleware import ( "context" "crypto/hmac" "crypto/sha256" "encoding/hex" "fmt" "net/http" "strconv" "strings" "time" "github.com/redis/go-redis/v9" ) const ( MaxEarlyDataWindow = 10 * time.Second HeaderEarlyData = "Early-Data" HeaderReplayToken = "X-Early-Data-Token" ) type AntiReplayValidator struct { rdb *redis.Client hmacSecret []byte } func NewAntiReplayValidator(rdb *redis.Client, secret []byte) *AntiReplayValidator { return &AntiReplayValidator{rdb: rdb, hmacSecret: secret} } func (v *AntiReplayValidator) Middleware(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { if r.Header.Get(HeaderEarlyData) != "1" { next.ServeHTTP(w, r) return } // Invariant 1: Reject non-safe methods in 0-RTT early data per RFC 8470 switch r.Method { case http.MethodGet, http.MethodHead, http.MethodOptions: // Safe/idempotent methods permitted under replay window verification default: w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Unsafe method in 0-RTT", http.StatusTooEarly) return } // Invariant 2: Validate temporal token (format: timestamp:nonce:signature) token := r.Header.Get(HeaderReplayToken) if token == "" { w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Missing replay protection token", http.StatusTooEarly) return } parts := strings.Split(token, ":") if len(parts) != 3 { http.Error(w, "Malformed replay token", http.StatusBadRequest) return } tsNano, err := strconv.ParseInt(parts[0], 10, 64) if err != nil { http.Error(w, "Invalid token timestamp", http.StatusBadRequest) return } tokenTime := time.Unix(0, tsNano) now := time.Now().UTC() if tokenTime.Before(now.Add(-MaxEarlyDataWindow)) || tokenTime.After(now.Add(MaxEarlyDataWindow)) { w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Token expired or outside window", http.StatusTooEarly) return } // Invariant 3: Verify HMAC integrity of timestamp + nonce h := hmac.New(sha256.New, v.hmacSecret) h.Write([]byte(fmt.Sprintf("%s:%s", parts[0], parts[1]))) expectedSig := hex.EncodeToString(h.Sum(nil)) if !hmac.Equal([]byte(parts[2]), []byte(expectedSig)) { http.Error(w, "Invalid replay signature", http.StatusUnauthorized) return } // Invariant 4: Atomic lock in distributed cache to guarantee uniqueness in window ctx := r.Context() key := fmt.Sprintf("0rtt:nonce:%s", parts[1]) success, err := v.rdb.SetNX(ctx, key, "1", MaxEarlyDataWindow*2).Result() if err != nil || !success { w.Header().Set("Retry-After", "0") http.Error(w, "Too Early: Replayed early data detected", http.StatusTooEarly) return } next.ServeHTTP(w, r) }) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 HTTP/3 0-RTT Distributed Anti-Replay Guardrail

Go 1.24 HTTP/3 0-RTT Distributed Anti-Replay Guardrail defines an industrial-grade behavioral standard for backend engineering. Enforces strict 0-RTT (Early Data) validation across Go HTTP/3 services to eliminate replay attacks at the edge. Guarantees that state-altering methods are rejected immediately with HTTP 425 (Too Early) and idempotent early data routes validate cryptographically signed temporal tokens against a distributed sliding 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: Unchecked HTTP/3 0-RTT Early Data execution enabling distributed request replay and duplicate side-effects. 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	Unchecked HTTP/3 0-RTT Early Data execution enabling distributed request replay and duplicate side-effects.	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 ('1') and underlying QUIC connection state to detect 0-RTT transmission.

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.