fix: use ring buffer for log reading

local/api/api.go

@@ -34,6 +34,7 @@ func Init(di *dig.Container, app *fiber.App) {
 		WebSocket:    groups.Group("/ws"),
 		Leaderboard:  serverIdGroup.Group("/leaderboard"),
 		Steam:        groups.Group("/steam"),
+		Log:          serverIdGroup.Group("/log"),
 	}
 
 	accessKeyMiddleware := middleware.NewAccessKeyMiddleware()

local/controller/controller.go

@@ -69,4 +69,9 @@ func InitializeControllers(c *dig.Container) {
 	if err != nil {
 		logging.Panic("unable to initialize steam controller")
 	}
+
+	err = c.Invoke(NewLogController)
+	if err != nil {
+		logging.Panic("unable to initialize log controller")
+	}
 }

local/controller/log.go

@@ -0,0 +1,62 @@
+package controller
+
+import (
+	"acc-server-manager/local/middleware"
+	"acc-server-manager/local/model"
+	"acc-server-manager/local/service"
+	"acc-server-manager/local/utl/common"
+	"acc-server-manager/local/utl/error_handler"
+	"strconv"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/google/uuid"
+)
+
+type LogController struct {
+	service      *service.ServerService
+	errorHandler *error_handler.ControllerErrorHandler
+}
+
+func NewLogController(ss *service.ServerService, routeGroups *common.RouteGroups, auth *middleware.AuthMiddleware) *LogController {
+	lc := &LogController{
+		service:      ss,
+		errorHandler: error_handler.NewControllerErrorHandler(),
+	}
+
+	logRoutes := routeGroups.Log
+	logRoutes.Use(auth.Authenticate)
+	logRoutes.Get("/", auth.HasPermission(model.ServerView), lc.GetLogLines)
+
+	return lc
+}
+
+// GetLogLines godoc
+// @Summary Get last N lines of server log
+// @Tags Server
+// @Param id path string true "Server ID"
+// @Param lines query int false "Number of lines to return (default 100)"
+// @Success 200 {object} object{lines=[]string}
+// @Security BearerAuth
+// @Router /server/{id}/log [get]
+func (lc *LogController) GetLogLines(c *fiber.Ctx) error {
+	serverIDStr := c.Params("id")
+	serverID, err := uuid.Parse(serverIDStr)
+	if err != nil {
+		return lc.errorHandler.HandleUUIDError(c, "server ID")
+	}
+
+	n, _ := strconv.Atoi(c.Query("lines", "100"))
+	if n <= 0 {
+		n = 100
+	}
+	if n > 10000 {
+		n = 10000
+	}
+
+	lines, err := lc.service.GetLastLogLines(c, serverID, n)
+	if err != nil {
+		return lc.errorHandler.HandleServiceError(c, err)
+	}
+
+	return c.JSON(fiber.Map{"lines": lines})
+}

local/model/websocket.go

@@ -33,6 +33,7 @@ const (
 	MessageTypeSteamOutput WebSocketMessageType = "steam_output"
 	MessageTypeError       WebSocketMessageType = "error"
 	MessageTypeComplete    WebSocketMessageType = "complete"
+	MessageTypeLogLine     WebSocketMessageType = "log_line"
 )
 
 type WebSocketMessage struct {
@@ -65,6 +66,10 @@ type CompleteMessage struct {
 	Message  string    `json:"message"`
 }
 
+type LogLineMessage struct {
+	Line string `json:"line"`
+}
+
 func GetStepDescription(step ServerCreationStep) string {
 	descriptions := map[ServerCreationStep]string{
 		StepValidation:        "Validating server configuration",

local/platform/interfaces.go

@@ -25,4 +25,5 @@ type FirewallManager interface {
 type LogStreamer interface {
 	Start(ctx context.Context, server *model.Server, handleLine func(string)) error
 	Stop(serverID uuid.UUID)
+	GetLastLines(ctx context.Context, server *model.Server, n int) ([]string, error)
 }

local/service/docker_log_streamer.go

@@ -6,6 +6,7 @@ import (
 	"bufio"
 	"context"
 	"io"
+	"strconv"
 	"sync"
 
 	"github.com/docker/docker/api/types"
@@ -72,3 +73,34 @@ func (s *DockerLogStreamer) Stop(serverID uuid.UUID) {
 		v.(context.CancelFunc)()
 	}
 }
+
+func (s *DockerLogStreamer) GetLastLines(ctx context.Context, server *model.Server, n int) ([]string, error) {
+	if n <= 0 || server.ContainerID == "" {
+		return []string{}, nil
+	}
+
+	rc, err := s.client.ContainerLogs(ctx, server.ContainerID, types.ContainerLogsOptions{
+		ShowStdout: true,
+		ShowStderr: true,
+		Tail:       strconv.Itoa(n),
+	})
+	if err != nil {
+		return nil, err
+	}
+	defer rc.Close()
+
+	pr, pw := io.Pipe()
+	go func() {
+		defer pw.Close()
+		if _, err := stdcopy.StdCopy(pw, pw, rc); err != nil && err != io.EOF {
+			logging.Warn("DockerLogStreamer.GetLastLines: stdcopy error for %s: %v", server.ServiceName, err)
+		}
+	}()
+
+	var lines []string
+	scanner := bufio.NewScanner(pr)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+	return lines, scanner.Err()
+}

local/service/file_log_streamer.go

@@ -3,7 +3,9 @@ package service
 import (
 	"acc-server-manager/local/model"
 	"acc-server-manager/local/utl/tracking"
+	"bufio"
 	"context"
+	"os"
 	"path/filepath"
 	"sync"
 
@@ -36,3 +38,40 @@ func (s *FileLogStreamer) Stop(serverID uuid.UUID) {
 		v.(*tracking.LogTailer).Stop()
 	}
 }
+
+func (s *FileLogStreamer) GetLastLines(_ context.Context, server *model.Server, n int) ([]string, error) {
+	if n <= 0 {
+		return []string{}, nil
+	}
+	logPath := filepath.Join(server.GetLogPath(), "server.log")
+	f, err := os.Open(logPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return []string{}, nil
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	ring := make([]string, n)
+	head := 0
+	count := 0
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		ring[head] = scanner.Text()
+		head = (head + 1) % n
+		if count < n {
+			count++
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+	if count < n {
+		return ring[:count], nil
+	}
+	out := make([]string, n)
+	copy(out, ring[head:])
+	copy(out[n-head:], ring[:head])
+	return out, nil
+}

local/service/server.go

@@ -47,12 +47,27 @@ type pendingState struct {
 
 func (s *ServerService) ensureLogTailing(server *model.Server, instance *tracking.AccServerInstance) {
 	go func() {
-		if err := s.logStreamer.Start(context.Background(), server, instance.HandleLogLine); err != nil {
+		handleFn := func(line string) {
+			instance.HandleLogLine(line)
+			s.webSocketService.BroadcastLogLine(server.ID, line)
+		}
+		if err := s.logStreamer.Start(context.Background(), server, handleFn); err != nil {
 			logging.Error("Failed to start log streaming for server %s: %v", server.ID, err)
 		}
 	}()
 }
 
+func (s *ServerService) GetLastLogLines(ctx *fiber.Ctx, serverID uuid.UUID, n int) ([]string, error) {
+	server, err := s.repository.GetByID(ctx.UserContext(), serverID)
+	if err != nil {
+		return nil, err
+	}
+	if n <= 0 {
+		n = 100
+	}
+	return s.logStreamer.GetLastLines(ctx.UserContext(), server, n)
+}
+
 func NewServerService(
 	repository *repository.ServerRepository,
 	stateHistoryRepo *repository.StateHistoryRepository,

local/service/websocket.go

@@ -103,6 +103,16 @@ func (ws *WebSocketService) BroadcastError(serverID uuid.UUID, error string, det
 	ws.broadcastToServer(serverID, wsMsg)
 }
 
+func (ws *WebSocketService) BroadcastLogLine(serverID uuid.UUID, line string) {
+	msg := model.WebSocketMessage{
+		Type:      model.MessageTypeLogLine,
+		ServerID:  &serverID,
+		Timestamp: time.Now().Unix(),
+		Data:      model.LogLineMessage{Line: line},
+	}
+	ws.broadcastToServer(serverID, msg)
+}
+
 func (ws *WebSocketService) BroadcastComplete(serverID uuid.UUID, success bool, message string) {
 	completeMsg := model.CompleteMessage{
 		ServerID: serverID,

local/utl/common/common.go

@@ -28,6 +28,7 @@ type RouteGroups struct {
 	WebSocket    fiber.Router
 	Leaderboard  fiber.Router
 	Steam        fiber.Router
+	Log          fiber.Router
 }
 
 func CheckError(err error) {