从零开始手写一个「开箱即用的大文件分片上传库」

一、写在前面

相信各位小伙伴在实际做业务的时候都遇到过「大文件上传」的场景。在这种场景下，我们不能直接将大文件直接丢给服务器进行处理，这会对服务器的性能产生巨大的影响，并且上传速度也过于缓慢。因此我们会采用「大文件分片上传」的技术方案，尽可能快地上传文件，并对服务器的性能产生尽可能小的影响。

刚好最近趁着业余时间，详细了解了下「大文件分片上传」的技术细节，发现已有的一些分片上传库的使用体验都不太好，因此在这里从零开始手写一个大文件分片上传库，一是加深理解，二是方便大家后续直接使用。

二、大文件分片上传技术方案

一般来说大文件分片上传主要有以下几个步骤：

1、前端计算文件 md5。计算文件的 md5 是为了检查上传到服务器的文件是否与用户所传的文件一致，同时也可以根据 md5 进行「秒传」等操作。

2、前端发送初始化请求，后端初始化上传。当计算好文件的 md5 后，就可以进入初始化上传的步骤，在这一步骤中，前端会发起初始化请求，包含这个文件计算的 md5、文件名等信息，而后端则会根据 md5 初始化接收分片文件的目录。

3、前端进行文件分片，并将分片传输给后端。这个步骤自不必多说，前端会将文件分成多个小块，并按照一定的策略进行上传，如果遇到上传失败的分片，需要重新上传。

4、前端发送结束上传请求，后端合并分片。当发送成功所有的文件分片后，前端会发起结束上传请求，后端收到请求后，会将已有的文件分片合并，生成文件，并确认生成的文件的 md5 是否与初始化传入的 md5 一致。

值得注意的是，当文件比较大时，直接根据文件「计算 md5」、「进行文件分片」、「合并文件」都是十分消耗内存的（甚至可能直接把内存吃满），因此在这三个步骤，需要使用流来减小内存上的消耗。

三、easy-file-uploader

先贴一下我用 Typescript 写的「开箱即用的大文件分片上传库」的地址吧：easy-file-uploader 源码地址[1]

具体使用方式可以直接点击上述地址，查看 README.md。

那么话不多说，让我们来看看这个库我具体是怎么实现的。

四、easy-file-uploader-server 实现过程

从刚才「大文件分片上传技术方案」中，我们可以明确后端首先要提供以下几个最基础的能力：

1、初始化文件上传

2、接收文件分片

3、合并文件分片

其次，为了使用体验，我们还需要提供如下附加能力：

4、获取已上传的分片信息

5、清理分片存储目录（用于取消上传）

因此，我们首先要写一个FileUploaderServer类，提供上述这些能力。这样，当开发者在使用easy-file-uploader-server的时候，只需要实例化FileUploaderServer类，并在接口中使用这个类提供的方法即可。

这样做是为了提供了更好的可拓展性——毕竟，开发者可能用 express/koa/原生 nodejs 等框架实现接口，如果我们挨个实现一遍。。。太不利于维护了。

那么我们能很快地写出来这个类的大框架，它大概长这样：

interface IFileUploaderOptions {
  tempFileLocation: string; // 分片存储路径
  mergedFileLocation: string; // 合并后的文件路径
}

class FileUploaderServer {
  private fileUploaderOptions: IFileUploaderOptions;

  /**
   * 初始化文件分片上传，实际上就是根据fileName和时间计算一个md5，并新建一个文件夹
   * @param fileName 文件名
   * @returns 上传Id
   */
  public async initFilePartUpload(fileName: string): Promise<string> {}

  /**
   * 上传分片，实际上是将partFile写入uploadId对应的文件夹中，写入的文件命名格式为`partIndex|md5`
   * @param uploadId 上传Id
   * @param partIndex 分片序号
   * @param partFile 分片内容
   * @returns 分片md5
   */
  public async uploadPartFile(
    uploadId: string,
    partIndex: number,
    partFile: Buffer,
  ): Promise<string> {}

  /**
   * 获取已上传的分片信息，实际上就是读取这个文件夹下面的内容
   * @param uploadId 上传Id
   * @returns 已上传的分片信息
   */
  public async listUploadedPartFile(
    uploadId: string,
  ): Promise<IUploadPartInfo[]> {}

  /**
   * 取消文件上传，硬删除会直接删除文件夹，软删除会给文件夹改个名字
   * @param uploadId 上传Id
   * @param deleteFolder 是否直接删除文件夹
   */
  async cancelFilePartUpload(
    uploadId: string,
    deleteFolder: boolean = false,
  ): Promise<void> {}

  /**
   * 完成分片上传，实际上就是将所有分片都读到一起，然后进行md5检查，最后存到一个新的路径下。
   * @param uploadId 上传Id
   * @param fileName 文件名
   * @param md5 文件md5
   * @returns 文件存储路径
   */
  async finishFilePartUpload(
    uploadId: string,
    fileName: string,
    md5: string,
  ): Promise<IMergedFileInfo> {}
}

4-1、初始化文件上传

在初始化上传的时候，我们要在tempFileLocation目录（也就是分片存储目录）下根据 md5 新建一个目录，用于保存上传的分片。这个目录名就是 uploadId，是根据${fileName}-${Date.now()}计算的 md5 值。

  /**
   * 初始化文件分片上传，实际上就是根据fileName和时间计算一个md5，并新建一个文件夹
   * @param fileName 文件名
   * @returns 上传Id
   */
  public async initFilePartUpload(fileName: string): Promise<string> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadId = calculateMd5(`${fileName}-${Date.now()}`);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (uploadFolderExist) {
      throw new FolderExistException(
        'found same upload folder, maybe you meet hash collision',
      );
    }
    await fse.mkdir(uploadFolderPath);
    return uploadId;
  }

4-2、接收文件分片

在接收文件分片的时候，我们首先会获取分片存储位置，然后计算分片的 md5，然后将分片命名为${partIndex}|${partFileMd5}.part，存储到对应路径下。

/**
   * 上传分片，实际上是将partFile写入uploadId对应的文件夹中，写入的文件命名格式为`partIndex|md5`
   * @param uploadId 上传Id
   * @param partIndex 分片序号
   * @param partFile 分片内容
   * @returns 分片md5
   */
  public async uploadPartFile(
    uploadId: string,
    partIndex: number,
    partFile: Buffer,
  ): Promise<string> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    const partFileMd5 = calculateMd5(partFile);
    const partFileLocation = path.join(
      uploadFolderPath,
      `${partIndex}|${partFileMd5}.part`,
    );
    await fse.writeFile(partFileLocation, partFile);
    return partFileMd5;
  }

4-3、合并文件分片

在合并文件分片时，最重要的就是下面这个mergePartFile方法，这个方法会使用readStream和writeStream来读取/写入文件分片，这样做的好处是能尽可能地减少内存占用。同时，使用MultiStream提供的pipe方法，来保证 stream 的顺序。

export async function mergePartFile(
  files: IFileInfo[],
  mergedFilePath: string,
): Promise<void> {
  const fileList = files.map((item) => {
    const [index] = item.name.replace(/\.part$/, '').split('|');
    return {
      index: parseInt(index),
      path: item.path,
    };
  });
  const sortedFileList = fileList.sort((a, b) => {
    return a.index - b.index;
  });
  const sortedFilePathList = sortedFileList.map((item) => item.path);
  merge(sortedFilePathList, mergedFilePath);
}

function merge(inputPathList: string[], outputPath: string) {
  const fd = fse.openSync(outputPath, 'w+');
  const writeStream = fse.createWriteStream(outputPath);
  const readStreamList = inputPathList.map((path) => {
    return fse.createReadStream(path);
  });
  return new Promise((resolve, reject) => {
    const multiStream = new MultiStream(readStreamList);
    multiStream.pipe(writeStream);
    multiStream.on('end', () => {
      fse.closeSync(fd);
      resolve(true);
    });
    multiStream.on('error', () => {
      fse.closeSync(fd);
      reject(false);
    });
  });
}

那么有了mergePartFile方法后，合并文件分片的finishFilePartUpload方法也就呼之欲出了，在mergePartFile的基础上，增加文件保存路径的获取以及 md5 的校验即可。

  /**
   * 完成分片上传，实际上就是将所有分片都读到一起，然后进行md5检查，最后存到一个新的路径下。
   * @param uploadId 上传Id
   * @param fileName 文件名
   * @param md5 文件md5
   * @returns 文件存储路径
   */
  async finishFilePartUpload(
    uploadId: string,
    fileName: string,
    md5: string,
  ): Promise<IMergedFileInfo> {
    const { mergedFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(mergedFileLocation);
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    const dirList = await listDir(uploadFolderPath);
    const files = dirList.filter((item) => item.path.endsWith('.part'));
    const mergedFileDirLocation = path.join(mergedFileLocation, md5);
    await fse.ensureDir(mergedFileDirLocation);
    const mergedFilePath = path.join(mergedFileDirLocation, fileName);
    await mergePartFile(files, mergedFilePath);
    await wait(1000); // 要等待一段时间，否则在计算md5时会读取到空文件
    const mergedFileMd5 = await calculateFileMd5(mergedFilePath);
    if (mergedFileMd5 !== md5) {
      throw new Md5Exception('md5 checked failed');
    }
    return {
      path: mergedFilePath,
      md5,
    };
  }

4-4、获取已上传的分片信息

获取已上传的分片信息实际上就是读取 uploadId 目录下所有后缀为 part 的分片文件，逻辑很简单，看代码就行。

 /**
   * 获取已上传的分片信息，实际上就是读取这个文件夹下面的内容
   * @param uploadId 上传Id
   * @returns 已上传的分片信息
   */
  public async listUploadedPartFile(
    uploadId: string,
  ): Promise<IUploadPartInfo[]> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    const dirList = await listDir(uploadFolderPath);
    const uploadPartInfo = dirList.map((item: IFileInfo) => {
      const [index, md5] = item.name.replace(/\.part$/, '').split('|');
      return {
        path: item.path,
        index: parseInt(index),
        md5,
      };
    });
    return uploadPartInfo;
  }

function listDir(path: string): Promise<IFileInfo[]> {
  const items = await fse.readdir(path);
  return Promise.all(
    items
      .filter((item: string) => !item.startsWith('.'))
      .map(async (item: string) => {
        return {
          name: item,
          path: `${path}/${item}`,
        };
      }),
  );
}

4-5、清理分片存储目录

清理分片存储目录实际上也很简单，如果是软删除，则直接为目录改个名字即可。如果是硬删除，那么就删掉这个目录。

  /**
   * 取消文件上传，硬删除会直接删除文件夹，软删除会给文件夹改个名字
   * @param uploadId 上传Id
   * @param deleteFolder 是否直接删除文件夹
   */
  async cancelFilePartUpload(
    uploadId: string,
    deleteFolder: boolean = false,
  ): Promise<void> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    if (deleteFolder) {
      await fse.remove(uploadFolderPath);
    } else {
      await fse.rename(uploadFolderPath, `${uploadFolderPath}[removed]`);
    }
  }

4-6、详细代码

那么把上述代码整合到一起，FileUploaderServer类就完成了。更详细的代码可通过上面的 github 地址去查看：点击这里[2]

import * as path from 'path';
import * as fse from 'fs-extra';
import {
  calculateFileMd5,
  calculateMd5,
  IFileInfo,
  listDir,
  mergePartFile,
  wait,
} from './util';
import {
  FolderExistException,
  Md5Exception,
  NotFoundException,
} from './exception';

const DEAFULT_TEMP_FILE_LOCATION = path.join(__dirname, './upload_file');
const DEAFULT_MERGED_FILE_LOCATION = path.join(__dirname, './merged_file');
const DEFAULT_OPTIONS = {
  tempFileLocation: DEAFULT_TEMP_FILE_LOCATION,
  mergedFileLocation: DEAFULT_MERGED_FILE_LOCATION,
};

export interface IFileUploaderOptions {
  tempFileLocation: string;
  mergedFileLocation: string;
}

export interface IUploadPartInfo {
  path: string;
  index: number;
  md5: string;
}

export interface IMergedFileInfo {
  path: string;
  md5: string;
}

export class FileUploaderServer {
  private fileUploaderOptions: IFileUploaderOptions;

  constructor(options: IFileUploaderOptions) {
    this.fileUploaderOptions = Object.assign(DEFAULT_OPTIONS, options);
  }

  public getOptions() {
    return this.fileUploaderOptions;
  }

  /**
   * 初始化文件分片上传，实际上就是根据fileName和时间计算一个md5，并新建一个文件夹
   * @param fileName 文件名
   * @returns 上传Id
   */
  public async initFilePartUpload(fileName: string): Promise<string> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadId = calculateMd5(`${fileName}-${Date.now()}`);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (uploadFolderExist) {
      throw new FolderExistException(
        'found same upload folder, maybe you meet hash collision',
      );
    }
    await fse.mkdir(uploadFolderPath);
    return uploadId;
  }

  /**
   * 上传分片，实际上是将partFile写入uploadId对应的文件夹中，写入的文件命名格式为`partIndex|md5`
   * @param uploadId 上传Id
   * @param partIndex 分片序号
   * @param partFile 分片内容
   * @returns 分片md5
   */
  public async uploadPartFile(
    uploadId: string,
    partIndex: number,
    partFile: Buffer,
  ): Promise<string> {
    const uploadFolderPath = await this.getUploadFolder(uploadId);
    const partFileMd5 = calculateMd5(partFile);
    const partFileLocation = path.join(
      uploadFolderPath,
      `${partIndex}|${partFileMd5}.part`,
    );
    await fse.writeFile(partFileLocation, partFile);
    return partFileMd5;
  }

  /**
   * 获取已上传的分片信息，实际上就是读取这个文件夹下面的内容
   * @param uploadId 上传Id
   * @returns 已上传的分片信息
   */
  public async listUploadedPartFile(
    uploadId: string,
  ): Promise<IUploadPartInfo[]> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    const dirList = await listDir(uploadFolderPath);
    const uploadPartInfo = dirList.map((item: IFileInfo) => {
      const [index, md5] = item.name.replace(/\.part$/, '').split('|');
      return {
        path: item.path,
        index: parseInt(index),
        md5,
      };
    });
    return uploadPartInfo;
  }

  /**
   * 取消文件上传，硬删除会直接删除文件夹，软删除会给文件夹改个名字
   * @param uploadId 上传Id
   * @param deleteFolder 是否直接删除文件夹
   */
  async cancelFilePartUpload(
    uploadId: string,
    deleteFolder: boolean = false,
  ): Promise<void> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    if (deleteFolder) {
      await fse.remove(uploadFolderPath);
    } else {
      await fse.rename(uploadFolderPath, `${uploadFolderPath}[removed]`);
    }
  }

  /**
   * 完成分片上传，实际上就是将所有分片都读到一起，然后进行md5检查，最后存到一个新的路径下。
   * @param uploadId 上传Id
   * @param fileName 文件名
   * @param md5 文件md5
   * @returns 文件存储路径
   */
  async finishFilePartUpload(
    uploadId: string,
    fileName: string,
    md5: string,
  ): Promise<IMergedFileInfo> {
    const { mergedFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(mergedFileLocation);
    const uploadFolderPath = await this.getUploadFolder(uploadId);
    const dirList = await listDir(uploadFolderPath);
    const files = dirList.filter((item) => item.path.endsWith('.part'));
    const mergedFileDirLocation = path.join(mergedFileLocation, md5);
    await fse.ensureDir(mergedFileDirLocation);
    const mergedFilePath = path.join(mergedFileDirLocation, fileName);
    await mergePartFile(files, mergedFilePath);
    await wait(1000); // 要等待一段时间，否则在计算md5时会读取到空文件
    const mergedFileMd5 = await calculateFileMd5(mergedFilePath);
    if (mergedFileMd5 !== md5) {
      throw new Md5Exception('md5 checked failed');
    }
    return {
      path: mergedFilePath,
      md5,
    };
  }

  /**
   * 获取上传文件夹的路径
   * @param uploadId 上传Id
   * @returns 文件夹路径
   */
  private async getUploadFolder(uploadId: string): Promise<string> {
    const { tempFileLocation } = this.fileUploaderOptions;
    await fse.ensureDir(tempFileLocation);
    const uploadFolderPath = path.join(tempFileLocation, uploadId);
    const uploadFolderExist = fse.existsSync(uploadFolderPath);
    if (!uploadFolderExist) {
      throw new NotFoundException('not found upload folder');
    }
    return uploadFolderPath;
  }
}

五、easy-file-uploader-client 实现过程

写完了后端逻辑，我们就可以开始写前端逻辑了。

就像上面说的，为了满足开发者对于扩展性的需要，easy-file-uploader-server提供的是「大文件分片上传」的能力，而不是直接提供「大文件分片上传」的接口。这就导致在设计easy-file-uploader-client时，不能直接发起请求。因此，easy-file-uploader-client在设计功能之初，就只预期提供对分片上传流程的把控，而不会对具体上传函数进行实现。

那么按照这个思路，easy-file-uploader-client需要提供如下基础能力：

1、文件 md5 计算及分片 2、支持用户自定义上传函数，并对这些上传函数的执行流程进行把控。

因此，我们首先要写一个FileUploaderClient类，提供上述这些能力。这样，当开发者在使用easy-file-uploader-client的时候，只需要实例化FileUploaderClient类，并在上传时使用提供的能力即可。当然，如果用户希望自己控制上传函数的执行流程，那么可以只用「文件 md5 计算及分片」的能力。

5-1、文件 md5 计算及分片

实现文件计算 md5 功能这里使用了spark-md5去计算文件的 md5 值。而分片的话，是使用浏览器自带的FileReader读取文件，然后用浏览器自带的 APIblobSlice去进行分片。

这里值得注意的是，因为当文件体积较大时，「直接对整个文件计算 md5」以及「直接加载整个文件并进行分片」都是很吃性能的操作，会耗时很久。这种时候我们同样也需要像easy-file-uploader-server一样，通过输入流对文件进行读取。

  /**
   * 将file对象进行分片，然后根据分片计算md5
   * @param file 要上传的文件
   * @returns 返回md5和分片列表
   */
  public async getChunkListAndFileMd5(
    file: File,
  ): Promise<{ md5: string; chunkList: Blob[] }> {
    return new Promise((resolve, reject) => {
      let currentChunk = 0;
      const chunkSize = this.fileUploaderClientOptions.chunkSize;
      const chunks = Math.ceil(file.size / chunkSize);
      const spark = new SparkMD5.ArrayBuffer();
      const fileReader = new FileReader();
      const blobSlice = getBlobSlice();
      const chunkList: Blob[] = [];

      fileReader.onload = function (e) {
        if (e?.target?.result instanceof ArrayBuffer) {
          spark.append(e.target.result);
        }
        currentChunk++;

        if (currentChunk < chunks) {
          loadNextChunk();
        } else {
          const computedHash = spark.end();
          resolve({ md5: computedHash, chunkList });
        }
      };

      fileReader.onerror = function (e) {
        console.warn('read file error', e);
        reject(e);
      };

      function loadNextChunk() {
        const start = currentChunk * chunkSize;
        const end =
          start + chunkSize >= file.size ? file.size : start + chunkSize;

        const chunk = blobSlice.call(file, start, end);
        chunkList.push(chunk);
        fileReader.readAsArrayBuffer(chunk);
      }

      loadNextChunk();
    });
  }

5-2、上传流程把控

把控上传流程实际上就比较简单了，首先我们需要开发者自行实现initFilePartUploadFunc、uploadPartFileFunc、finishFilePartUploadFunc三个函数，然后将它们作为配置项传入FileUploaderClient。最后，我们再提供一个uploadFile函数，依次执行配置项中的这三个函数，就能完成大文件分片上传的整个流程了。

整体上传流程其实比较简单： 1、执行getChunkListAndFileMd5，对文件进行分片并计算 md5。 2、执行initFilePartUploadFunc，初始化文件上传。 3、对每一个分片都执行一次uploadPartFileFunc，如果失败，则将其加入retryList。 4、对retryList中上传失败的分片进行重试。 5、执行finishFilePartUploadFunc，完成文件上传。

 /**
   * 上传文件方法，当FileUploaderClient的配置项中传入了requestOptions才能使用
   * 会依次执行getChunkListAndFileMd5、配置项中的initFilePartUploadFunc、配置项中的uploadPartFileFunc、配置项中的finishFilePartUploadFunc
   * 执行完成后返回上传结果，若有分片上传失败，则会自动重试
   * @param file 要上传的文件
   * @returns finishFilePartUploadFunc函数Promise resolve的值
   */
  public async uploadFile(file: File): Promise<any> {
    const requestOptions = this.fileUploaderClientOptions.requestOptions;
    const { md5, chunkList } = await this.getChunkListAndFileMd5(file);
    const retryList = [];

    if (
      requestOptions?.retryTimes === undefined ||
      !requestOptions?.initFilePartUploadFunc ||
      !requestOptions?.uploadPartFileFunc ||
      !requestOptions?.finishFilePartUploadFunc
    ) {
      throw Error(
        'invalid request options, need retryTimes, initFilePartUploadFunc, uploadPartFileFunc and finishFilePartUploadFunc',
      );
    }

    await requestOptions.initFilePartUploadFunc();

    for (let index = 0; index < chunkList.length; index++) {
      try {
        await requestOptions.uploadPartFileFunc(chunkList[index], index);
      } catch (e) {
        console.warn(`${index} part upload failed`);
        retryList.push(index);
      }
    }

    for (let retry = 0; retry < requestOptions.retryTimes; retry++) {
      if (retryList.length > 0) {
        console.log(`retry start, times: ${retry}`);
        for (let a = 0; a < retryList.length; a++) {
          const blobIndex = retryList[a];
          try {
            await requestOptions.uploadPartFileFunc(
              chunkList[blobIndex],
              blobIndex,
            );
            retryList.splice(a, 1);
          } catch (e) {
            console.warn(
              `${blobIndex} part retry upload failed, times: ${retry}`,
            );
          }
        }
      }
    }

    if (retryList.length === 0) {
      return await requestOptions.finishFilePartUploadFunc(md5);
    } else {
      throw Error(
        `upload failed, some chunks upload failed: ${JSON.stringify(
          retryList,
        )}`,
      );
    }
  }

5-3、总体代码

把上述代码整合到一起，FileUploaderClient 类就完成了。更详细的代码可通过上面的 github 地址去查看：点击这里[3]

import SparkMD5 from 'spark-md5';
import { getBlobSlice } from './util';

const DEFAULT_CHUNK_SIZE = 5 * 1024 * 1024;
const DEFAULT_OPTIONS = {
  chunkSize: DEFAULT_CHUNK_SIZE,
};

export interface IFileUploaderClientOptions {
  chunkSize: number;
  requestOptions?: {
    retryTimes: number;
    initFilePartUploadFunc: () => Promise<any>;
    uploadPartFileFunc: (chunk: Blob, index: number) => Promise<any>;
    finishFilePartUploadFunc: (md5: string) => Promise<any>;
  };
}

export class FileUploaderClient {
  fileUploaderClientOptions: IFileUploaderClientOptions;

  constructor(options: IFileUploaderClientOptions) {
    this.fileUploaderClientOptions = Object.assign(DEFAULT_OPTIONS, options);
  }

  /**
   * 将file对象进行分片，然后根据分片计算md5
   * @param file 要上传的文件
   * @returns 返回md5和分片列表
   */
  public async getChunkListAndFileMd5(
    file: File,
  ): Promise<{ md5: string; chunkList: Blob[] }> {
    return new Promise((resolve, reject) => {
      let currentChunk = 0;
      const chunkSize = this.fileUploaderClientOptions.chunkSize;
      const chunks = Math.ceil(file.size / chunkSize);
      const spark = new SparkMD5.ArrayBuffer();
      const fileReader = new FileReader();
      const blobSlice = getBlobSlice();
      const chunkList: Blob[] = [];

      fileReader.onload = function (e) {
        if (e?.target?.result instanceof ArrayBuffer) {
          spark.append(e.target.result);
        }
        currentChunk++;

        if (currentChunk < chunks) {
          loadNextChunk();
        } else {
          const computedHash = spark.end();
          resolve({ md5: computedHash, chunkList });
        }
      };

      fileReader.onerror = function (e) {
        console.warn('read file error', e);
        reject(e);
      };

      function loadNextChunk() {
        const start = currentChunk * chunkSize;
        const end =
          start + chunkSize >= file.size ? file.size : start + chunkSize;

        const chunk = blobSlice.call(file, start, end);
        chunkList.push(chunk);
        fileReader.readAsArrayBuffer(chunk);
      }

      loadNextChunk();
    });
  }

  /**
   * 上传文件方法，当FileUploaderClient的配置项中传入了requestOptions才能使用
   * 会依次执行getChunkListAndFileMd5、配置项中的initFilePartUploadFunc、配置项中的uploadPartFileFunc、配置项中的finishFilePartUploadFunc
   * 执行完成后返回上传结果，若有分片上传失败，则会自动重试
   * @param file 要上传的文件
   * @returns finishFilePartUploadFunc函数Promise resolve的值
   */
  public async uploadFile(file: File): Promise<any> {
    const requestOptions = this.fileUploaderClientOptions.requestOptions;
    const { md5, chunkList } = await this.getChunkListAndFileMd5(file);
    const retryList = [];

    if (
      requestOptions?.retryTimes === undefined ||
      !requestOptions?.initFilePartUploadFunc ||
      !requestOptions?.uploadPartFileFunc ||
      !requestOptions?.finishFilePartUploadFunc
    ) {
      throw Error(
        'invalid request options, need retryTimes, initFilePartUploadFunc, uploadPartFileFunc and finishFilePartUploadFunc',
      );
    }

    await requestOptions.initFilePartUploadFunc();

    for (let index = 0; index < chunkList.length; index++) {
      try {
        await requestOptions.uploadPartFileFunc(chunkList[index], index);
      } catch (e) {
        console.warn(`${index} part upload failed`);
        retryList.push(index);
      }
    }

    for (let retry = 0; retry < requestOptions.retryTimes; retry++) {
      if (retryList.length > 0) {
        console.log(`retry start, times: ${retry}`);
        for (let a = 0; a < retryList.length; a++) {
          const blobIndex = retryList[a];
          try {
            await requestOptions.uploadPartFileFunc(
              chunkList[blobIndex],
              blobIndex,
            );
            retryList.splice(a, 1);
          } catch (e) {
            console.warn(
              `${blobIndex} part retry upload failed, times: ${retry}`,
            );
          }
        }
      }
    }

    if (retryList.length === 0) {
      return await requestOptions.finishFilePartUploadFunc(md5);
    } else {
      throw Error(
        `upload failed, some chunks upload failed: ${JSON.stringify(
          retryList,
        )}`,
      );
    }
  }
}

六、试用一下！

6-1、server 端

先用 koa 写一个 server 吧，easy-file-uploader-server的使用方式可以重点可以看下 router 配置

const Koa = require('koa')
const bodyParser = require('koa-bodyparser')
const router = require('./router')
const cors = require('@koa/cors')
const staticResource = require('koa-static')
const path = require('path')
const KoaRouter = require('koa-router')
const multer = require('@koa/multer')
const path = require('path')
const { FileUploaderServer } = require('easy-file-uploader-server')

const PORT = 10001

const app = new Koa()

const upload = multer()
const router = KoaRouter()

const fileUploader = new FileUploaderServer({
  tempFileLocation: path.join(__dirname, './public/tempUploadFile'),
  mergedFileLocation: path.join(__dirname, './public/mergedUploadFile'),
})

router.post('/api/initUpload', async (ctx, next) => {
  const { name } = ctx.request.body
  const uploadId = await fileUploader.initFilePartUpload(name)
  ctx.body = { uploadId }
  await next()
})

router.post('/api/uploadPart', upload.single('partFile'), async (ctx, next) => {
  const { buffer } = ctx.file
  const { uploadId, partIndex } = ctx.request.body
  const partFileMd5 = await fileUploader.uploadPartFile(uploadId, partIndex, buffer)
  ctx.body = { partFileMd5 }
  await next()
})

router.post('/api/finishUpload', async (ctx, next) => {
  const { uploadId, name, md5 } = ctx.request.body
  const { path: filePathOnServer } = await fileUploader.finishFilePartUpload(uploadId, name, md5)
  const suffix = filePathOnServer.split('/public/')[1]
  ctx.body = { path: suffix }
  await next()
})

app.use(<span data-word-id="828" class="abbreviate-word">cors</span>())
app.use(bodyParser())
app.use(staticResource(path.join(__dirname, 'public')))
app.use(router.routes())
app.use(router.allowedMethods())
app.listen(PORT)
console.log(`app run in port: ${PORT}`)
console.log(`visit http://localhost:${PORT}/index.html to start demo`)

6-2、client 端

再用 react 写一个 client 吧，重点可以看下 APP 组件中的逻辑。

import { useRef, useState } from 'react'
import './App.<span data-word-id="51586836" class="abbreviate-word">css</span>'
import axios from 'axios'
import { FileUploaderClient } from 'easy-file-uploader-client'

const HOST = 'http://localhost:10001/'

function App() {
  const fileInput = useRef(null)
  const [url, setUrl] = useState<string>('')
  let uploadId = ''

  const fileUploaderClient = new FileUploaderClient({
    chunkSize: 2 * 1024 * 1024, // 2MB
    requestOptions: {
      retryTimes: 2,
      initFilePartUploadFunc: async () => {
        const fileName = (fileInput.current as any).files[0].name
        const { data } = await axios.post(`${HOST}api/initUpload`, {
          name: fileName,
        })
        uploadId = data.uploadId
        console.log('初始化上传完成')
        setUrl('')
      },
      uploadPartFileFunc: async (chunk: Blob, index: number) => {
        const formData = new FormData()
        formData.append('uploadId', uploadId)
        formData.append('partIndex', index.toString())
        formData.append('partFile', chunk)

        await axios.post(`${HOST}api/uploadPart`, formData, {
          headers: { 'Content-Type': 'multipart/form-data' },
        })
        console.log(`上传分片 ${index}完成`)
      },
      finishFilePartUploadFunc: async (md5: string) => {
        const fileName = (fileInput.current as any).files[0].name
        const { data } = await axios.post(`${HOST}api/finishUpload`, {
          name: fileName,
          uploadId,
          md5,
        })
        console.log(`上传完成，存储地址为：${HOST}${data.path}`)
        setUrl(`${HOST}${data.path}`)
      },
    },
  })

  const upload = () => {
    if (fileInput.current) {
      fileUploaderClient.uploadFile((fileInput.current as any).files[0])
    }
  }

  return (
    <div className="App">
      <h1>easy-file-uploader-demo</h1>
      <h3>选择文件后点击“上传文件”按钮即可</h3>
      <div className="App">
        <input type="file" name="file" ref={fileInput} />
        <input type="button" value="上传文件" onClick={upload} />
      </div>
      {url && <h3>{`文件地址：${url}`}</h3>}
    </div>
  )
}

export default App

6-3、使用效果

首先选择大文件，然后点击上传，上传完毕后显示了文件地址。

访问一下文件，看起来文件已经成功上传到服务器了，完美！

更详细的使用样例可以到 github 中查看：easy-file-uploader 使用样例[4]

参考资料

[1] easy-file-uploader 源码地址: https://github.com/shadowings-zy/easy-file-uploader

[2] 点击这里: https://github.com/shadowings-zy/easy-file-uploader/tree/master/package/fileUploaderServer

[3] 点击这里: https://github.com/shadowings-zy/easy-file-uploader/tree/master/package/fileUploaderClient

[4] easy-file-uploader 使用样例: https://github.com/shadowings-zy/easy-file-uploader/tree/master/demo