Add client connection rate limit

1 files changed, 25 insertions, 1 deletions

diff --git a/hotline/server.go b/hotline/server.go
index 5531bd3..758f7ff 100644
--- a/hotline/server.go
+++ b/hotline/server.go
@@ -9,6 +9,7 @@ import (
 	"errors"
 	"fmt"
 	"golang.org/x/text/encoding/charmap"
+	"golang.org/x/time/rate"
 	"io"
 	"log"
 	"log/slog"
@@ -37,6 +38,8 @@ type Server struct {
 	NetInterface string
 	Port         int
 
+	rateLimiters map[string]*rate.Limiter
+
 	handlers map[TranType]HandlerFunc
 
 	Config Config
@@ -98,6 +101,7 @@ func NewServer(options ...Option) (*Server, error) {
 	server := Server{
 		handlers:        make(map[TranType]HandlerFunc),
 		outbox:          make(chan Transaction),
+		rateLimiters:    make(map[string]*rate.Limiter),
 		FS:              &OSFileStore{},
 		ChatMgr:         NewMemChatManager(),
 		ClientMgr:       NewMemClientMgr(),
@@ -202,6 +206,10 @@ func (s *Server) processOutbox() {
 	}
 }
 
+// perIPRateLimit controls how frequently an IP address can connect before being throttled.
+// 0.5 = 1 connection every 2 seconds
+const perIPRateLimit = rate.Limit(0.5)
+
 func (s *Server) Serve(ctx context.Context, ln net.Listener) error {
 	for {
 		select {
@@ -216,13 +224,29 @@ func (s *Server) Serve(ctx context.Context, ln net.Listener) error {
 			}
 
 			go func() {
+				ipAddr := strings.Split(conn.RemoteAddr().(*net.TCPAddr).String(), ":")[0]
+
 				connCtx := context.WithValue(ctx, contextKeyReq, requestCtx{
 					remoteAddr: conn.RemoteAddr().String(),
 				})
 
-				s.Logger.Info("Connection established", "addr", conn.RemoteAddr())
+				s.Logger.Info("Connection established", "ip", ipAddr)
 				defer conn.Close()
 
+				// Check if we have an existing rate limit for the IP and create one if we do not.
+				rl, ok := s.rateLimiters[ipAddr]
+				if !ok {
+					rl = rate.NewLimiter(perIPRateLimit, 1)
+					s.rateLimiters[ipAddr] = rl
+				}
+
+				// Check if the rate limit is exceeded and close the connection if so.
+				if !rl.Allow() {
+					s.Logger.Info("Rate limit exceeded", "RemoteAddr", conn.RemoteAddr())
+					conn.Close()
+					return
+				}
+
 				if err := s.handleNewConnection(connCtx, conn, conn.RemoteAddr().String()); err != nil {
 					if err == io.EOF {
 						s.Logger.Info("Client disconnected", "RemoteAddr", conn.RemoteAddr())