iris/community

So the correct code is:

app.Post("/upload", func(ctx iris.Context) {
        // Set a lower memory limit for multipart forms (default is 32 MiB)
        ctx.SetMaxRequestBodySize(maxSize)
        // OR
        // app.Use(iris.LimitRequestBodySize(maxSize))
        // OR
        // OR iris.WithPostMaxMemory(maxSize)

        // single file
        file, fileHeader, err:= ctx.FormFile("file")
        if err != nil {
            ctx.StopWithError(iris.StatusBadRequest, err)
            return
        }

        // 这个地方应该使用fileHeader来获取文件名(go 1.15version).
       //我不知道是不是go的版本的问题，我没有去查看go之前的版本
        dest := filepath.Join("./uploads", fileHeader.Filename)
        ctx.SaveFormFile(file, dest)

        ctx.Writef("File: %s uploaded!", file.Filename)
    })

and the ctx.FormFile source code is:

func (ctx *Context) FormFile(key string) (multipart.File, *multipart.FileHeader, error) {
    // we don't have access to see if the request is body stream
    // and then the ParseMultipartForm can be useless
    // here but do it in order to apply the post limit,
    // the internal request.FormFile will not do it if that's filled
    // and it's not a stream body.
    if err := ctx.request.ParseMultipartForm(ctx.app.ConfigurationReadOnly().GetPostMaxMemory()); err != nil {
        return nil, nil, err
    }

    return ctx.request.FormFile(key)
}