control: harden HTTP server timeouts

cmd/fmrtx/main.go

@@ -5,7 +5,6 @@ import (
 	"flag"
 	"fmt"
 	"log"
-	"net/http"
 	"os"
 	"os/signal"
 	"syscall"
@@ -109,8 +108,9 @@ func main() {
 
 	// --- default: HTTP only ---
 	srv := ctrlpkg.NewServer(cfg)
-	log.Printf("fm-rds-tx listening on %s (TX default: off, use --tx for hardware)", cfg.Control.ListenAddress)
-	log.Fatal(http.ListenAndServe(cfg.Control.ListenAddress, srv.Handler()))
+	server := ctrlpkg.NewHTTPServer(cfg, srv.Handler())
+	log.Printf("fm-rds-tx listening on %s (TX default: off, use --tx for hardware)", server.Addr)
+	log.Fatal(server.ListenAndServe())
 }
 
 // selectDriver picks the best available driver based on config and build tags.
@@ -228,9 +228,10 @@ func runTXMode(cfg cfgpkg.Config, driver platform.SoapyDriver, autoStart bool, a
 		log.Println("TX ready (idle) — POST /tx/start to begin")
 	}
 
+	ctrlServer := ctrlpkg.NewHTTPServer(cfg, srv.Handler())
 	go func() {
-		log.Printf("control plane on %s", cfg.Control.ListenAddress)
-		if err := http.ListenAndServe(cfg.Control.ListenAddress, srv.Handler()); err != nil {
+		log.Printf("control plane on %s (read=%s write=%s idle=%s)", ctrlServer.Addr, ctrlServer.ReadTimeout, ctrlServer.WriteTimeout, ctrlServer.IdleTimeout)
+		if err := ctrlServer.ListenAndServe(); err != nil {
 			log.Printf("http: %v", err)
 		}
 	}()

docs/README.md

@@ -87,6 +87,8 @@ All major TX parameters are hot-reloadable via `POST /config` during live transm
 
 Available endpoints: `/healthz`, `/status`, `/runtime`, `/config` (GET/POST), `/dry-run`, `/tx/start`, `/tx/stop`
 
+Control-plane HTTP server is configured with 5s read, 10s write, and 60s idle timeouts plus a 1 MiB header limit to reduce slow-client abuse.
+
 ### Internal DSP module
 - `cd internal`
 - `go test ./...`

internal/control/server.go

@@ -0,0 +1,27 @@
+package control
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/jan/fm-rds-tx/internal/config"
+)
+
+const (
+	defaultReadTimeout    = 5 * time.Second
+	defaultWriteTimeout   = 10 * time.Second
+	defaultIdleTimeout    = 60 * time.Second
+	defaultMaxHeaderBytes = 1 << 20 // 1 MiB
+)
+
+// NewHTTPServer returns a configured HTTP server for the control plane.
+func NewHTTPServer(cfg config.Config, handler http.Handler) *http.Server {
+	return &http.Server{
+		Addr:           cfg.Control.ListenAddress,
+		Handler:        handler,
+		ReadTimeout:    defaultReadTimeout,
+		WriteTimeout:   defaultWriteTimeout,
+		IdleTimeout:    defaultIdleTimeout,
+		MaxHeaderBytes: defaultMaxHeaderBytes,
+	}
+}

internal/control/server_test.go

@@ -0,0 +1,33 @@
+package control
+
+import (
+	"net/http"
+	"testing"
+
+	cfgpkg "github.com/jan/fm-rds-tx/internal/config"
+)
+
+func TestNewHTTPServerConfig(t *testing.T) {
+	cfg := cfgpkg.Default()
+	handler := http.NewServeMux()
+	srv := NewHTTPServer(cfg, handler)
+
+	if srv.Addr != cfg.Control.ListenAddress {
+		t.Fatalf("expected server address %q, got %q", cfg.Control.ListenAddress, srv.Addr)
+	}
+	if srv.Handler != handler {
+		t.Fatalf("expected handler to be preserved")
+	}
+	if srv.ReadTimeout != defaultReadTimeout {
+		t.Fatalf("expected read timeout %s, got %s", defaultReadTimeout, srv.ReadTimeout)
+	}
+	if srv.WriteTimeout != defaultWriteTimeout {
+		t.Fatalf("expected write timeout %s, got %s", defaultWriteTimeout, srv.WriteTimeout)
+	}
+	if srv.IdleTimeout != defaultIdleTimeout {
+		t.Fatalf("expected idle timeout %s, got %s", defaultIdleTimeout, srv.IdleTimeout)
+	}
+	if srv.MaxHeaderBytes != defaultMaxHeaderBytes {
+		t.Fatalf("expected max header bytes %d, got %d", defaultMaxHeaderBytes, srv.MaxHeaderBytes)
+	}
+}