Add structured logging and centralized error handling

- Initialize slog in the serve command with terminal/file support
- Introduce `AppError` with HTTP status for unified service-layer errors
- Replace ad-hoc `api.Error` calls with `api.RespondError`
- Wrap internal errors with `model.NewInternalError` and add reference
  IDs
- Add `RequestID` middleware and switch router from `gin.Default` to
  `gin.New`

internal/handler/file.go

@@ -1,9 +1,9 @@
 package handler
 
 import (
-	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"mime"
 	"net/http"
 	"net/url"
@@ -49,13 +49,14 @@ func (h *FileHandler) Upload(c *gin.Context) {
 	if mediaType == "application/json" {
 		var req createDirRequest
 		if err := c.ShouldBindJSON(&req); err != nil {
-			api.Error(c, http.StatusBadRequest, "invalid request: "+err.Error())
+			slog.DebugContext(c.Request.Context(), "create dir bind failed", "error", err)
+			api.Error(c, http.StatusBadRequest, "invalid request body")
 			return
 		}
 
 		dir, err := h.fileService.CreateDir(c.Request.Context(), userID, req.ParentID, req.Name)
 		if err != nil {
-			api.Error(c, mapError(err), err.Error())
+			api.RespondError(c, err)
 			return
 		}
 
@@ -65,7 +66,8 @@ func (h *FileHandler) Upload(c *gin.Context) {
 
 	// File upload via multipart.
 	if err := c.Request.ParseMultipartForm(32 << 20); err != nil {
-		api.Error(c, http.StatusBadRequest, "invalid multipart form: "+err.Error())
+		slog.DebugContext(c.Request.Context(), "parse multipart form failed", "error", err)
+		api.Error(c, http.StatusBadRequest, "invalid multipart form")
 		return
 	}
 
@@ -77,20 +79,21 @@ func (h *FileHandler) Upload(c *gin.Context) {
 
 	header, err := c.FormFile("file")
 	if err != nil {
-		api.Error(c, http.StatusBadRequest, "missing file field: "+err.Error())
+		slog.DebugContext(c.Request.Context(), "form file missing", "error", err)
+		api.Error(c, http.StatusBadRequest, "missing file field")
 		return
 	}
 
 	file, err := header.Open()
 	if err != nil {
-		api.Error(c, http.StatusInternalServerError, "open uploaded file: "+err.Error())
+		api.RespondError(c, model.NewInternalError("open uploaded file", err))
 		return
 	}
 	defer file.Close()
 
 	info, err := h.fileService.Upload(c.Request.Context(), userID, parentID, header.Filename, file)
 	if err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -124,7 +127,7 @@ func (h *FileHandler) List(c *gin.Context) {
 
 	list, err := h.fileService.List(c.Request.Context(), userID, parentID, offset, limit)
 	if err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -138,7 +141,7 @@ func (h *FileHandler) Get(c *gin.Context) {
 
 	info, err := h.fileService.Get(c.Request.Context(), userID, fileID)
 	if err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -152,7 +155,7 @@ func (h *FileHandler) Download(c *gin.Context) {
 
 	reader, info, err := h.fileService.Download(c.Request.Context(), userID, fileID)
 	if err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 	defer reader.Close()
@@ -177,7 +180,8 @@ func (h *FileHandler) Update(c *gin.Context) {
 
 	var req updateFileRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
-		api.Error(c, http.StatusBadRequest, "invalid request: "+err.Error())
+		slog.DebugContext(c.Request.Context(), "update file bind failed", "error", err)
+		api.Error(c, http.StatusBadRequest, "invalid request body")
 		return
 	}
 
@@ -189,7 +193,7 @@ func (h *FileHandler) Update(c *gin.Context) {
 
 	info, err := h.fileService.Update(c.Request.Context(), userID, fileID, req.Name, req.ParentID)
 	if err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
@@ -202,23 +206,9 @@ func (h *FileHandler) Delete(c *gin.Context) {
 	fileID := c.Param("id")
 
 	if err := h.fileService.Delete(c.Request.Context(), userID, fileID); err != nil {
-		api.Error(c, mapError(err), err.Error())
+		api.RespondError(c, err)
 		return
 	}
 
 	c.Status(http.StatusNoContent)
 }
-
-// mapError maps sentinel errors to HTTP status codes.
-func mapError(err error) int {
-	switch {
-	case errors.Is(err, model.ErrNotFound):
-		return http.StatusNotFound
-	case errors.Is(err, model.ErrForbidden):
-		return http.StatusForbidden
-	case errors.Is(err, model.ErrDuplicate):
-		return http.StatusConflict
-	default:
-		return http.StatusInternalServerError
-	}
-}