Golang 文件上传中如何使用自定义错误消息？

import "fmt"

// FileUploadError represents an error that occurred during file upload.
type FileUploadError struct {
    Message string
}

// Error returns the error message.
func (e *FileUploadError) Error() string {
    return fmt.Sprintf("File upload error: %s", e.Message)
}

func uploadFile(file *multipart.FileHeader) error {
    // 检查文件大小
    if file.Size > maxFileSize {
        return &FileUploadError{Message: "File is too large."}
    }

    // 检查文件类型
    if !allowedFileTypes[file.Header.Get("Content-Type")] {
        return &FileUploadError{Message: "Invalid file type."}
    }

    // 上传文件...
}

import (
    "fmt"
    "github.com/labstack/echo/v4"
    "github.com/labstack/echo/v4/middleware"
    "net/http"
    "os"
)

// FileUploadError represents an error that occurred during file upload.
type FileUploadError struct {
    Message string
}

// Error returns the error message.
func (e *FileUploadError) Error() string {
    return fmt.Sprintf("File upload error: %s", e.Message)
}

func uploadFile(c echo.Context) error {
    // 检查文件大小
    file, err := c.FormFile("file")
    if err != nil {
        return err
    }
    if file.Size > maxFileSize {
        return &FileUploadError{Message: "File is too large."}
    }

    // 检查文件类型
    if !allowedFileTypes[file.Header.Get("Content-Type")] {
        return &FileUploadError{Message: "Invalid file type."}
    }

    // 上传文件...
    f, err := os.OpenFile(file.Filename, os.O_WRONLY|os.O_CREATE, 0666)
    if err != nil {
        return err
    }
    defer f.Close()
    if _, err = f.Write(file.Bytes()); err != nil {
        return err
    }
    return c.JSON(http.StatusOK, map[string]interface{}{
        "status": "success",
    })
}

func main() {
    e := echo.New()
    e.Use(middleware.BodyLimit("10mb"))
    e.POST("/upload", uploadFile)
    e.Logger.Fatal(e.Start(":1323"))
}