Add Blossom bandwidth limiting and tune rate limiters (v0.49.0)

- Add token-bucket bandwidth rate limiting for Blossom uploads
  - ORLY_BLOSSOM_RATE_LIMIT enables limiting (default: false)
  - ORLY_BLOSSOM_DAILY_LIMIT_MB sets daily limit (default: 10MB)
  - ORLY_BLOSSOM_BURST_LIMIT_MB sets burst cap (default: 50MB)
  - Followed users, admins, owners are exempt (unlimited)
- Change emergency mode throttling from exponential to linear scaling
  - Old: 16x multiplier at emergency threshold entry
  - New: 1x at threshold, +1x per 20% excess pressure
- Reduce follows ACL throttle increment from 200ms to 25ms per event
- Update dependencies

Files modified:
- app/blossom.go: Pass rate limit config to blossom server
- app/config/config.go: Add Blossom rate limit config options
- pkg/blossom/ratelimit.go: New bandwidth limiter implementation
- pkg/blossom/server.go: Add rate limiter integration
- pkg/blossom/handlers.go: Check rate limits on upload/mirror/media
- pkg/ratelimit/limiter.go: Linear emergency throttling
- pkg/acl/follows.go: Reduce default throttle increment

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/blossom/handlers.go

@@ -200,6 +200,12 @@ func (s *Server) handleUpload(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Check bandwidth rate limit (non-followed users)
+	if !s.checkBandwidthLimit(pubkey, remoteAddr, int64(len(body))) {
+		s.setErrorResponse(w, http.StatusTooManyRequests, "upload rate limit exceeded, try again later")
+		return
+	}
+
 	// Calculate SHA256 after auth check
 	sha256Hash := CalculateSHA256(body)
 	sha256Hex := hex.Enc(sha256Hash)
@@ -647,6 +653,12 @@ func (s *Server) handleMirror(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Check bandwidth rate limit (non-followed users)
+	if !s.checkBandwidthLimit(pubkey, remoteAddr, int64(len(body))) {
+		s.setErrorResponse(w, http.StatusTooManyRequests, "upload rate limit exceeded, try again later")
+		return
+	}
+
 	// Note: pubkey may be nil for anonymous uploads if ACL allows it
 
 	// Detect MIME type from remote response
@@ -726,6 +738,12 @@ func (s *Server) handleMediaUpload(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Check bandwidth rate limit (non-followed users)
+	if !s.checkBandwidthLimit(pubkey, remoteAddr, int64(len(body))) {
+		s.setErrorResponse(w, http.StatusTooManyRequests, "upload rate limit exceeded, try again later")
+		return
+	}
+
 	// Note: pubkey may be nil for anonymous uploads if ACL allows it
 
 	// Optimize media (placeholder - actual optimization would be implemented here)

pkg/blossom/ratelimit.go

@@ -0,0 +1,131 @@
+package blossom
+
+import (
+	"sync"
+	"time"
+)
+
+// BandwidthState tracks upload bandwidth for an identity
+type BandwidthState struct {
+	BucketBytes   int64     // Current token bucket level (bytes available)
+	LastUpdate    time.Time // Last time bucket was updated
+}
+
+// BandwidthLimiter implements token bucket rate limiting for uploads.
+// Each identity gets a bucket that replenishes at dailyLimit/day rate.
+// Uploads consume tokens from the bucket.
+type BandwidthLimiter struct {
+	mu           sync.Mutex
+	states       map[string]*BandwidthState // keyed by pubkey hex or IP
+	dailyLimit   int64                      // bytes per day
+	burstLimit   int64                      // max bucket size (burst capacity)
+	refillRate   float64                    // bytes per second refill rate
+}
+
+// NewBandwidthLimiter creates a new bandwidth limiter.
+// dailyLimitMB is the average daily limit in megabytes.
+// burstLimitMB is the maximum burst capacity in megabytes.
+func NewBandwidthLimiter(dailyLimitMB, burstLimitMB int64) *BandwidthLimiter {
+	dailyBytes := dailyLimitMB * 1024 * 1024
+	burstBytes := burstLimitMB * 1024 * 1024
+
+	return &BandwidthLimiter{
+		states:     make(map[string]*BandwidthState),
+		dailyLimit: dailyBytes,
+		burstLimit: burstBytes,
+		refillRate: float64(dailyBytes) / 86400.0, // bytes per second
+	}
+}
+
+// CheckAndConsume checks if an upload of the given size is allowed for the identity,
+// and if so, consumes the tokens. Returns true if allowed, false if rate limited.
+// The identity should be pubkey hex for authenticated users, or IP for anonymous.
+func (bl *BandwidthLimiter) CheckAndConsume(identity string, sizeBytes int64) bool {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+
+	now := time.Now()
+	state, exists := bl.states[identity]
+
+	if !exists {
+		// New identity starts with full burst capacity
+		state = &BandwidthState{
+			BucketBytes: bl.burstLimit,
+			LastUpdate:  now,
+		}
+		bl.states[identity] = state
+	} else {
+		// Refill bucket based on elapsed time
+		elapsed := now.Sub(state.LastUpdate).Seconds()
+		refill := int64(elapsed * bl.refillRate)
+		state.BucketBytes += refill
+		if state.BucketBytes > bl.burstLimit {
+			state.BucketBytes = bl.burstLimit
+		}
+		state.LastUpdate = now
+	}
+
+	// Check if upload fits in bucket
+	if state.BucketBytes >= sizeBytes {
+		state.BucketBytes -= sizeBytes
+		return true
+	}
+
+	return false
+}
+
+// GetAvailable returns the currently available bytes for an identity.
+func (bl *BandwidthLimiter) GetAvailable(identity string) int64 {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+
+	state, exists := bl.states[identity]
+	if !exists {
+		return bl.burstLimit // New users have full capacity
+	}
+
+	// Calculate current level with refill
+	now := time.Now()
+	elapsed := now.Sub(state.LastUpdate).Seconds()
+	refill := int64(elapsed * bl.refillRate)
+	available := state.BucketBytes + refill
+	if available > bl.burstLimit {
+		available = bl.burstLimit
+	}
+
+	return available
+}
+
+// GetTimeUntilAvailable returns how long until the given bytes will be available.
+func (bl *BandwidthLimiter) GetTimeUntilAvailable(identity string, sizeBytes int64) time.Duration {
+	available := bl.GetAvailable(identity)
+	if available >= sizeBytes {
+		return 0
+	}
+
+	needed := sizeBytes - available
+	seconds := float64(needed) / bl.refillRate
+	return time.Duration(seconds * float64(time.Second))
+}
+
+// Cleanup removes entries that have fully replenished (at burst limit).
+func (bl *BandwidthLimiter) Cleanup() {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+
+	now := time.Now()
+	for key, state := range bl.states {
+		elapsed := now.Sub(state.LastUpdate).Seconds()
+		refill := int64(elapsed * bl.refillRate)
+		if state.BucketBytes+refill >= bl.burstLimit {
+			delete(bl.states, key)
+		}
+	}
+}
+
+// Stats returns the number of tracked identities.
+func (bl *BandwidthLimiter) Stats() int {
+	bl.mu.Lock()
+	defer bl.mu.Unlock()
+	return len(bl.states)
+}

pkg/blossom/server.go

@@ -19,6 +19,9 @@ type Server struct {
 	maxBlobSize      int64
 	allowedMimeTypes map[string]bool
 	requireAuth      bool
+
+	// Rate limiting for uploads
+	bandwidthLimiter *BandwidthLimiter
 }
 
 // Config holds configuration for the Blossom server
@@ -27,6 +30,11 @@ type Config struct {
 	MaxBlobSize      int64
 	AllowedMimeTypes []string
 	RequireAuth      bool
+
+	// Rate limiting (for non-followed users)
+	RateLimitEnabled bool
+	DailyLimitMB     int64
+	BurstLimitMB     int64
 }
 
 // NewServer creates a new Blossom server instance
@@ -48,6 +56,20 @@ func NewServer(db *database.D, aclRegistry *acl.S, cfg *Config) *Server {
 		}
 	}
 
+	// Initialize bandwidth limiter if enabled
+	var bwLimiter *BandwidthLimiter
+	if cfg.RateLimitEnabled {
+		dailyMB := cfg.DailyLimitMB
+		if dailyMB <= 0 {
+			dailyMB = 10 // 10MB default
+		}
+		burstMB := cfg.BurstLimitMB
+		if burstMB <= 0 {
+			burstMB = 50 // 50MB default burst
+		}
+		bwLimiter = NewBandwidthLimiter(dailyMB, burstMB)
+	}
+
 	return &Server{
 		db:               db,
 		storage:          storage,
@@ -56,6 +78,7 @@ func NewServer(db *database.D, aclRegistry *acl.S, cfg *Config) *Server {
 		maxBlobSize:      cfg.MaxBlobSize,
 		allowedMimeTypes: allowedMap,
 		requireAuth:      cfg.RequireAuth,
+		bandwidthLimiter: bwLimiter,
 	}
 }
 
@@ -208,6 +231,44 @@ func (s *Server) checkACL(
 	return actual >= required
 }
 
+// isRateLimitExempt returns true if the user is exempt from rate limiting.
+// Users with write access or higher (followed users, admins, owners) are exempt.
+func (s *Server) isRateLimitExempt(pubkey []byte, remoteAddr string) bool {
+	if s.acl == nil {
+		return true // No ACL configured, no rate limiting
+	}
+
+	level := s.acl.GetAccessLevel(pubkey, remoteAddr)
+
+	// Followed users get "write" level, admins/owners get higher
+	// Only "read" and "none" are rate limited
+	return level == "write" || level == "admin" || level == "owner"
+}
+
+// checkBandwidthLimit checks if the upload is allowed under rate limits.
+// Returns true if allowed, false if rate limited.
+// Exempt users (followed, admin, owner) always return true.
+func (s *Server) checkBandwidthLimit(pubkey []byte, remoteAddr string, sizeBytes int64) bool {
+	if s.bandwidthLimiter == nil {
+		return true // No rate limiting configured
+	}
+
+	// Check if user is exempt
+	if s.isRateLimitExempt(pubkey, remoteAddr) {
+		return true
+	}
+
+	// Use pubkey hex if available, otherwise IP
+	var identity string
+	if len(pubkey) > 0 {
+		identity = string(pubkey) // Will be converted to hex in handler
+	} else {
+		identity = remoteAddr
+	}
+
+	return s.bandwidthLimiter.CheckAndConsume(identity, sizeBytes)
+}
+
 // BaseURLKey is the context key for the base URL (exported for use by app handler)
 type BaseURLKey struct{}