perf: rate limiter cleanup goroutine, DB pool constraints

- ipLimiter evicts stale entries after 10 min of inactivity via 5 min sweep
- DB pool capped at 25 max open, 5 idle, 15 min lifetime

internal/db/db.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"time"
 
 	"git.dustin.coffee/hobokenchicken/dumpsterChat/internal/config"
 
@@ -24,6 +25,11 @@ func New(cfg *config.Config) (*DB, error) {
 		return nil, fmt.Errorf("ping database: %w", err)
 	}
 
+	// ponytail: prevent unbounded connection growth under burst load
+	db.SetMaxOpenConns(25)
+	db.SetMaxIdleConns(5)
+	db.SetConnMaxLifetime(15 * time.Minute)
+
 	return &DB{db}, nil
 }
 

internal/middleware/ratelimit.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"strings"
 	"sync"
+	"time"
 
 	"golang.org/x/time/rate"
 )
@@ -12,16 +13,21 @@ import (
 type ipLimiter struct {
 	mu       sync.Mutex
 	limiters map[string]*rate.Limiter
+	lastUsed map[string]time.Time
 	rate     rate.Limit
 	burst    int
 }
 
 func newIPLimiter(r rate.Limit, burst int) *ipLimiter {
-	return &ipLimiter{
+	l := &ipLimiter{
 		limiters: make(map[string]*rate.Limiter),
+		lastUsed: make(map[string]time.Time),
 		rate:     r,
 		burst:    burst,
 	}
+	// ponytail: evict inactive limiters every 5 minutes to prevent unbounded map growth
+	go l.cleanup()
+	return l
 }
 
 func (l *ipLimiter) getLimiter(ip string) *rate.Limiter {
@@ -33,9 +39,27 @@ func (l *ipLimiter) getLimiter(ip string) *rate.Limiter {
 		lim = rate.NewLimiter(l.rate, l.burst)
 		l.limiters[ip] = lim
 	}
+	l.lastUsed[ip] = time.Now()
 	return lim
 }
 
+// cleanup runs in a background goroutine and removes limiters that haven't
+// been accessed in 10 minutes.
+func (l *ipLimiter) cleanup() {
+	for {
+		time.Sleep(5 * time.Minute)
+		l.mu.Lock()
+		now := time.Now()
+		for ip, last := range l.lastUsed {
+			if now.Sub(last) > 10*time.Minute {
+				delete(l.limiters, ip)
+				delete(l.lastUsed, ip)
+			}
+		}
+		l.mu.Unlock()
+	}
+}
+
 // RateLimit returns middleware that limits requests per IP.
 // requestsPerSecond is the sustained rate, burst is the max burst size.
 func RateLimit(requestsPerSecond float64, burst int) func(http.Handler) http.Handler {