.Net Web API 006 Controller上传大文件

1、上传大文件的方式

上传大文件就需要一段一段的上传，主要是先在客户端获取文件的大小，例如想一次传256kb，那就按照256kb分割。分割后又两种上传方式。

（1）逐个数据段读取，然后调用API上传，把数据追加到文件上。上传完这一段，接着传下一段，直到上传完毕。

（2）方式与（1）类似，只是可以好几段可以并行上传，上传后，会把每段按照索引命名，在服务器上保存成临时文件。判断都上传完毕后，再调用合并命令，把这些小的碎文件，合并成大的目标文件。

我一般喜欢用第一种方式，主要是因为简单明了。缺点就是，因为必须等上一段完成后，再传下一段，所以无法并行上传，导致速度会受到影响。

但我参与的项目基本上都是在局域网运行并且使用人数有限，所以这种传大文件的方式是可以满足系统要求。

2、上传大文件API实现

下面的实现用到了定义的AttachedFileEntity和HttpClientEx，这两个类的定义可参考 005 Controller上传小文件。

分三步，开始上传、循环上传二进制段、结束上传。

开始上传API的目的是为了获取文件在服务器上的存储路径，代码如下。

/// <summary>
/// 开始大上传文件
/// </summary>
/// <returns></returns>
[HttpPost]
[Route("StartUploadBigFile")]
public IActionResult StartUploadBigFile(AttachedFileEntity pEntity, string pFileEx)
{
    string myServerFilePath = DateTime.Now.ToString("yyyy_MM_dd") + "\\" + Guid.NewGuid().ToString() + pFileEx;
    pEntity.ServerPath = myServerFilePath;
    return this.Ok(pEntity);
}

分段上传文件，接收到后，追加到现有的文件上。

/// <summary>
/// 上传大文件
/// </summary>
/// <param name="pServerPath"></param>
/// <returns></returns>
[HttpPost]
[Route("UploadBigFile")]
[DisableRequestSizeLimit]
public IActionResult UploadBigFile(string pServerPath)
{
    var myFile = Request.Form.Files[0];

    //创建目录
    string myFullServerPath = AppDomain.CurrentDomain.BaseDirectory + "\\Files\\" + pServerPath;
    string myFullFolder = Path.GetDirectoryName(myFullServerPath)!;
    if (Directory.Exists(myFullFolder) == false)
    {
        Directory.CreateDirectory(myFullFolder);
    }

    //写入文件
    Stream? myStream = null;
    FileStream? myFileStream = null;
    BinaryWriter? myBinaryWriter = null;
    try
    {
        myStream = myFile.OpenReadStream();
        byte[] myBytes = new byte[myStream.Length];
        myStream.Read(myBytes, 0, myBytes.Length);
        myStream.Seek(0, SeekOrigin.Begin);

        myFileStream = new FileStream(myFullServerPath, FileMode.Append);
        myBinaryWriter = new BinaryWriter(myFileStream);
        myBinaryWriter.Write(myBytes);
    }
    catch (Exception ex)
    {
        return this.BadRequest("上传大文件失败," + ex.Message);
    }
    finally
    {
        myBinaryWriter?.Close();
        myFileStream?.Close();
        myStream?.Close();
    }

    return this.Ok();
}

最后，结束上传，把文件的信息记录到数据库中。

/// <summary>
/// 结束上传大文件
/// </summary>
/// <returns></returns>
[HttpPost]
[Route("FinishUploadBigFile")]
public IActionResult FinishUploadBigFile(AttachedFileEntity pEntity)
{
    if (string.IsNullOrEmpty(pEntity.GUID))
    {
        pEntity.GUID = Guid.NewGuid().ToString();
    }
    //记录到数据库中
    //代码略
    return this.Ok(pEntity);
}

3、客户端调用

客户端如果用的C#，代码中没有加入进度信息，进度信息可以传入一个ProcessInfo对象，传一段数据后，就更新下进度信息。

调用的代码入下所示。

private void Init_BigFileUpLoad_UIs()
{
    this.UI_BigFile_Button.Click += (x, y) =>
    {
        var myOpenFileDialog = new OpenFileDialog
        {
            Filter = ".*|*.*"
        };
        var myIsOK = myOpenFileDialog.ShowDialog();
        if (myIsOK != true)
        {
            return;
        }
        this.UI_BigFile_TextBox.Text = myOpenFileDialog.FileName;
    };

    this.UI_BigFileUpLoad_Button.Click += async (x, y) =>
    {
        var myFilePath = this.UI_BigFile_TextBox.Text.Trim();
        if (myFilePath.Length == 0)
        {
            MessageBox.Show("请选择一个文件。");
            return;
        }
        if (File.Exists(myFilePath) == false)
        {
            MessageBox.Show("文件不存在，请重新选择。");
            return;
        }

        //定义AttachedFileEntity
        var myFileEntity = new AttachedFileEntity()
        {
            GUID = Guid.NewGuid().ToString(),
            Name = "用户头像",
            KeyWord = "UserProfilePhoto",
            Description = "",
            EntityGUID = "AAAA"
        };

        //打开上传的文件
        var myFileStream = new FileStream(myFilePath, FileMode.Open);
        myFileEntity.FileSize = (int)myFileStream.Length;
        var myFileName = Path.GetFileName(myFilePath);

        //每次上传256kb
        int myChunkSize = 1024 * 256;
        int myChunkCount = (int)Math.Ceiling(myFileStream.Length / (double)myChunkSize);

        //调用开始上传
        var myHttpClient = new HttpClient();
        var myHttpClientEx = new HttpClientEx(myHttpClient)
        {
            Url = "http://localhost:5000/api/AttachedFile/StartUploadBigFile",
            HttpContent = JsonContent.Create(myFileEntity)
        };
        myHttpClientEx.ParameterDictionary.Add("pFileEx", Path.GetExtension(myFileName));
        await myHttpClientEx.PostAsync();
        if (myHttpClientEx.IsSuccess == false)
        {
            myFileStream.Close();
            MessageBox.Show("上传文件失败，" + myHttpClientEx.ResponseContenString);
            return;
        }
        myFileEntity = myHttpClientEx.GetResponseObject<AttachedFileEntity>();
        if (myFileEntity == null)
        {
            myFileStream.Close();
            MessageBox.Show("上传文件失败，返回的AttachedFileEntity为null。");
            return;
        }

        //循环上传文件
        for (int i = 0; i < myChunkCount; i++)
        {
            //组织数据
            int myByteArraySize = myChunkSize;
            if (i == myChunkCount - 1)
            {
                myByteArraySize = (int)(myFileStream.Length % myChunkSize);
            }
            byte[] myBytes = new byte[myByteArraySize];
            myFileStream.Position = myChunkSize * i;
            myFileStream.Read(myBytes, 0, myBytes.Length);
            var myMemoryStream = new MemoryStream(myBytes);

            //请求服务
            myHttpClientEx = new HttpClientEx(myHttpClient)
            {
                Url = "http://localhost:5000/api/AttachedFile/UploadBigFile",
                HttpContent = new MultipartFormDataContent
                    {
                        {new StreamContent(myMemoryStream),"pFile",myFileName}
                    }
            };
            myHttpClientEx.ParameterDictionary.Add("pServerPath", myFileEntity!.ServerPath);
            await myHttpClientEx.PostAsync();

            //解析结果
            if (myHttpClientEx.IsSuccess == false)
            {
                myFileStream.Close();
                MessageBox.Show("上传文件失败，" + myHttpClientEx.ResponseContenString);
                return;
            }
        }

        //结束上传
        myHttpClientEx = new HttpClientEx(myHttpClient)
        {
            Url = "http://localhost:5000/api/AttachedFile/FinishUploadBigFile",
            HttpContent = JsonContent.Create<AttachedFileEntity>(myFileEntity)
        };
        await myHttpClientEx.PostAsync();
        if (myHttpClientEx.IsSuccess == false)
        {
            myFileStream.Close();
            MessageBox.Show("上传文件失败，" + myHttpClientEx.ResponseContenString);
            return;
        }
        myFileStream.Close();
        myFileEntity = myHttpClientEx.GetResponseObject<AttachedFileEntity>();
        var myEntityJosnString = JsonSerializer.Serialize<AttachedFileEntity>(myFileEntity);
        MessageBox.Show(myEntityJosnString);
    };
}

如果客户端是js，代码如下。

on(myButton, "change", function (e) {
    var myFileReader = new FileReader();
    var myFileName = "";

    myFileReader.onloadend = function () {
        var myFileResult = myFileReader.result;
        var myFileLength = myFileResult.byteLength;

        var myPerLength = 1024 * 256;
        var myCount = Math.ceil(myFileLength / myPerLength);

        var myFileEntity = new Object()
        {
            ServerPath: ""
        };

        //调用开始上传StartUploadBigFile，具体代码略。

        var myK = 0;
        Upload();

        function Upload() {

            var myByteArray = myFileResult.slice(myPerLength * myK, myPerLength * (myK + 1));
            var myBlob = new Blob([myByteArray]);
            var myFile = new File([myBlob], myFileName);
            var myFormData = new FormData();
            myFormData.append("file", myFile)
            request.post(myUrl + "?pServerFile=" + myFileEntity.ServerPath +, {
                data: myFormData
            }).then(function (data) {
                myFileEntity = json.parse(data);
                myK++;
                if (myK < myCount) {
                    Upload();
                }
                else {
                    alert("上传大文件结束。");
                    alert(json.stringify(myFileEntity));
                    //结束，post FinishUploadBigFile
                }

            }, function (err) {
                alert(err);
                return;
            });
        }
    }

    myFileName = this.files[0].name;
    myFileReader.readAsArrayBuffer(this.files[0]);
});

Js代码没有实际测试，只是一个思路。