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feat(backend): IP-based rate limiting middleware #14
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,43 @@ | ||
| --- | ||
| topic: middleware | ||
| last_verified: 2026-06-15 | ||
| sources: | ||
| - internal/transport/middleware/logger.go | ||
| - internal/transport/middleware/ratelimit.go | ||
| - internal/transport/handlers/routes.go | ||
| --- | ||
|
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| # Middleware | ||
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| All middleware lives in `internal/transport/middleware/` and follows the Gin `HandlerFunc` pattern. Middleware is registered in `RegisterRoutes()` inside `internal/transport/handlers/routes.go`. | ||
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| ## Registration order | ||
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| ```go | ||
| // 1. Recovery + logger (debug: gin.Logger, release: middleware.Logger) | ||
| r.Use(gin.Recovery(), middleware.Logger()) | ||
| // 2. Rate limiter (no-op when RPS <= 0) | ||
| r.Use(middleware.RateLimit(rps, burst)) | ||
| // 3. CORS | ||
| r.Use(cors.New(...)) | ||
| ``` | ||
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| ## Logger | ||
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| `Logger() gin.HandlerFunc` emits one structured `slog` record per request after `c.Next()` returns. Fields: `status`, `method`, `path`, `latency`, `ip`, and optionally `query` and `errors`. | ||
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| In debug mode (`ENV` not set to `staging`/`production`) Gin's built-in colorful logger is used instead. | ||
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| ## Rate limiter | ||
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| `RateLimit(rps float64, burst int) gin.HandlerFunc` limits each client IP to `rps` requests per second using a token-bucket algorithm (`golang.org/x/time/rate`). Each IP gets its own `rate.Limiter` stored in a mutex-guarded map. | ||
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| - **Disabled** when `rps <= 0` (no-op middleware returned). | ||
| - **429 Too Many Requests** returned when the bucket is empty; body: `{"error": "rate limit exceeded"}`. | ||
| - Configured via env vars `RATE_LIMIT_RPS` and `RATE_LIMIT_BURST` (see [environment](environment.md)). | ||
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| ## Adding new middleware | ||
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| 1. Create `internal/transport/middleware/<name>.go` with a function returning `gin.HandlerFunc`. | ||
| 2. Register it in `RegisterRoutes()` in `internal/transport/handlers/routes.go` at the appropriate position in the chain. | ||
| 3. If it requires configuration, add fields to `bootstrap.Config` and read from env in `loadConfig()`. |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| package middleware | ||
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| import ( | ||
| "net/http" | ||
| "sync" | ||
| "time" | ||
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| "github.com/gin-gonic/gin" | ||
| "golang.org/x/time/rate" | ||
| ) | ||
|
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| const ( | ||
| limiterTTL = 10 * time.Minute | ||
| cleanupInterval = 5 * time.Minute | ||
| ) | ||
|
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| type ipLimiter struct { | ||
| limiter *rate.Limiter | ||
| lastSeen time.Time | ||
| } | ||
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| // RateLimit returns a Gin middleware that limits each client IP to rps requests per | ||
| // second with the given burst size. When rps <= 0 the middleware is a no-op. | ||
| // Burst is clamped to a minimum of 1 so fractional rps values never block all traffic. | ||
| // Stale per-IP entries are evicted every 5 minutes. | ||
| func RateLimit(rps float64, burst int) gin.HandlerFunc { | ||
| if rps <= 0 { | ||
| return func(c *gin.Context) { c.Next() } | ||
| } | ||
| if burst < 1 { | ||
| burst = 1 | ||
| } | ||
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| var mu sync.Mutex | ||
| limiters := make(map[string]*ipLimiter) | ||
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| go func() { | ||
| ticker := time.NewTicker(cleanupInterval) | ||
| defer ticker.Stop() | ||
| for range ticker.C { | ||
| cutoff := time.Now().Add(-limiterTTL) | ||
| mu.Lock() | ||
| for ip, l := range limiters { | ||
| if l.lastSeen.Before(cutoff) { | ||
| delete(limiters, ip) | ||
| } | ||
| } | ||
| mu.Unlock() | ||
| } | ||
| }() | ||
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| getLimiter := func(ip string) *rate.Limiter { | ||
| mu.Lock() | ||
| defer mu.Unlock() | ||
| l, ok := limiters[ip] | ||
| if !ok { | ||
| l = &ipLimiter{limiter: rate.NewLimiter(rate.Limit(rps), burst)} | ||
| limiters[ip] = l | ||
| } | ||
| l.lastSeen = time.Now() | ||
| return l.limiter | ||
| } | ||
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| return func(c *gin.Context) { | ||
| if !getLimiter(c.ClientIP()).Allow() { | ||
| c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{"error": "rate limit exceeded"}) | ||
| return | ||
| } | ||
| c.Next() | ||
| } | ||
| } |
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