原文地址：

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ImageWriter.Helper{    public class WriterHelper    {        public enum ImageFormat        {            bmp,            jpeg,            gif,            tiff,            png,            unknown        }        public static ImageFormat GetImageFormat(byte[] bytes)        {            var bmp = Encoding.ASCII.GetBytes("BM");     // BMP            var gif = Encoding.ASCII.GetBytes("GIF");    // GIF            var png = new byte[] { 137, 80, 78, 71 };              // PNG            var tiff = new byte[] { 73, 73, 42 };                  // TIFF            var tiff2 = new byte[] { 77, 77, 42 };                 // TIFF            var jpeg = new byte[] { 255, 216, 255, 224 };          // jpeg            var jpeg2 = new byte[] { 255, 216, 255, 225 };         // jpeg canon            if (bmp.SequenceEqual(bytes.Take(bmp.Length)))                return ImageFormat.bmp;            if (gif.SequenceEqual(bytes.Take(gif.Length)))                return ImageFormat.gif;            if (png.SequenceEqual(bytes.Take(png.Length)))                return ImageFormat.png;            if (tiff.SequenceEqual(bytes.Take(tiff.Length)))                return ImageFormat.tiff;            if (tiff2.SequenceEqual(bytes.Take(tiff2.Length)))                return ImageFormat.tiff;            if (jpeg.SequenceEqual(bytes.Take(jpeg.Length)))                return ImageFormat.jpeg;            if (jpeg2.SequenceEqual(bytes.Take(jpeg2.Length)))                return ImageFormat.jpeg;            return ImageFormat.unknown;        }    }}

 IImageWriter.cs 

using Microsoft.AspNetCore.Http;using System.Threading.Tasks;namespace ImageWriter.Interface{    public interface IImageWriter    {        Task
     
       UploadImage(IFormFile file);    }}
     

using System;using System.Collections.Generic;using System.IO;using System.Text;using System.Threading.Tasks;using ImageWriter.Helper;using ImageWriter.Interface;using Microsoft.AspNetCore.Http;namespace ImageWriter.Classes{    public class ImageWriter : IImageWriter    {        public async Task
     
       UploadImage(IFormFile file)        {            if (CheckIfImageFile(file))            {                return await WriteFile(file);            }            return "Invalid image file";        }        /// 
      
        /// Method to check if file is image file        /// 
        /// 
              /// 
              private bool CheckIfImageFile(IFormFile file)        {            byte[] fileBytes;            using (var ms = new MemoryStream())            {                file.CopyTo(ms);                fileBytes = ms.ToArray();            }            return WriterHelper.GetImageFormat(fileBytes) != WriterHelper.ImageFormat.unknown;        }        /// 
      
        /// Method to write file onto the disk        /// 
        /// 
              /// 
              public async Task
      
        WriteFile(IFormFile file)        {            string fileName;            try            {                var extension = "." + file.FileName.Split('.')[file.FileName.Split('.').Length - 1];                fileName = Guid.NewGuid().ToString() + extension; //Create a new Name                                                               //for the file due to security reasons.                var path = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot\\images", fileName);                using (var bits = new FileStream(path, FileMode.Create))                {                    await file.CopyToAsync(bits);                }            }            catch (Exception e)            {                return e.Message;            }            return fileName;        }    }}
      
     

using System.Threading.Tasks;using ImageWriter.Interface;using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;namespace ImageUploader.Handler{    public interface IImageHandler    {        Task
     
       UploadImage(IFormFile file);    }    public class ImageHandler : IImageHandler    {        private readonly IImageWriter _imageWriter;        public ImageHandler(IImageWriter imageWriter)        {            _imageWriter = imageWriter;        }        public async Task
      
        UploadImage(IFormFile file)        {            var result = await _imageWriter.UploadImage(file);            return new ObjectResult(result);        }    }}
      
     

using System.Threading.Tasks;using ImageUploader.Handler;using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;namespace ImageUploader.Controllers{    [Route("api/image")]    public class ImagesController : Controller    {        private readonly IImageHandler _imageHandler;        public ImagesController(IImageHandler imageHandler)        {            _imageHandler = imageHandler;        }        /// 
        /// Uplaods an image to the server.        /// 
        ///         /// 
             public async Task
     
       UploadImage(IFormFile file)        {            return await _imageHandler.UploadImage(file);        }    }}
     

public void Configure(IApplicationBuilder app, IHostingEnvironment env)        {            if (env.IsDevelopment())            {                app.UseDeveloperExceptionPage();            }            else            {                app.UseHsts();            }            //Use this to set path of files outside the wwwroot folder            //app.UseStaticFiles(new StaticFileOptions            //{            //    FileProvider = new PhysicalFileProvider(            //        Path.Combine(Directory.GetCurrentDirectory(), "StaticFiles")),            //    RequestPath = "/StaticFiles"            //});            app.UseStaticFiles(); //letting the application know that we need access to wwwroot folder.            app.UseHttpsRedirection();            app.UseMvc();        }// This method gets called by the runtime. Use this method to add services to the container.        public void ConfigureServices(IServiceCollection services)        {            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);            services.AddTransient
     
      ();            services.AddTransient
      
       ();        }