文件的详解断点续传功能可以应用于需要上传或下载大文件的场景。在网络状况不佳或者文件较大时，实现一次性上传或下载整个文件可能会耗费大量时间和带宽，文点上并且可能会导致因中断而失败的传下情况发生。通过实现文件的详解断点续传功能，可以将大文件分割成小块，实现分别上传或下载，文点上即使在网络出现问题时也可以通过上传或下载已经完成的传下文件块来继续未完成的操作，减少耗时和带宽消耗，详解提高用户体验。实现常见的文点上应用场景如：视频、音频文件的上传或下载，大型软件的更新或下载，云盘等文件存储服务等等。
在asp.net core 中实现文件的断点续传功能，需要进行以下步骤：
具体实现思路如下：
在 ASP.NET Core 应用程序中，创建一个名为 UploadController 的控制器。在该控制器中，使用 ApiControllerAttribute 特性声明该控制器为 Web API 控制器。
[ApiController][Route("[controller]")]public class UploadController : ControllerBase在控制器中实现下面的代码。
[HttpPost]public async Task<IActionResult> Upload(IFormFile file, int chunkIndex, int totalChunks){ if (file == null || file.Length == 0) { return BadRequest("This request does not have any body"); } // create the folder if it doesn't exist yet string folderPath = Path.Combine(Directory.GetCurrentDirectory(), "Uploads"); if (!Directory.Exists(folderPath)) { Directory.CreateDirectory(folderPath); } string filePath = Path.Combine(folderPath, file.FileName); using (FileStream stream = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.Write)) { await file.CopyToAsync(stream); } return Ok();}在上面的代码中，我们只是将整个文件保存到了服务器上。现在，我们需要实现断点上传的逻辑。断点上传指的是，将大文件分成多个小块，并逐个上传。
using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;using System;using System.IO;using System.Threading.Tasks;namespace ResumeTransfer{ [Route("api/[controller]")] [ApiController] public class UploadController : ControllerBase { private const string UploadsFolder = "Uploads"; [HttpPost] public async Task<IActionResult> Upload(IFormFile file, int? chunkIndex, int? totalChunks) { if (file == null || file.Length == 0) { return BadRequest("This request does not have any body"); } // Check if the chunk index and total chunks are provided. if (!chunkIndex.HasValue || chunkIndex.Value < 0 || !totalChunks.HasValue || totalChunks.Value <= 0) { return BadRequest("Invalid chunk index or total chunks"); } // Create folder for upload files if not exists string folderPath = Path.Combine(Directory.GetCurrentDirectory(), UploadsFolder); if (!Directory.Exists(folderPath)) { Directory.CreateDirectory(folderPath); } string filePath = Path.Combine(folderPath, file.FileName); // Check if chunk already exists if (System.IO.File.Exists(GetChunkFileName(filePath, chunkIndex.Value))) { return Ok(); } using (FileStream stream = new FileStream(GetChunkFileName(filePath, chunkIndex.Value), FileMode.Create, FileAccess.Write, FileShare.Write)) { await file.CopyToAsync(stream); } if (chunkIndex == totalChunks - 1) { // All the chunks have been uploaded, merge them into a single file MergeChunks(filePath, totalChunks.Value); } return Ok(); } private void MergeChunks(string filePath, int totalChunks) { using (var finalStream = new FileStream(filePath, FileMode.CreateNew)) { for (int i = 0; i < totalChunks; i++) { var chunkFileName = GetChunkFileName(filePath, i); using (var stream = new FileStream(chunkFileName, FileMode.Open)) { stream.CopyTo(finalStream); } System.IO.File.Delete(chunkFileName); } } } private string GetChunkFileName(string filePath, int chunkIndex) { return $"{ filePath}.part{ chunkIndex.ToString().PadLeft(5, '0')}"; } }}客户端使用 axios 库进行文件上传。使用下面的代码，将文件分块并管理每个文件块的大小和数量。
// get file size and nameconst fileSize = file.size;const fileName = file.name;// calculate chunk sizeconst chunkSize = 10 * 1024 * 1024; // 10MB// calculate total chunksconst totalChunks = Math.ceil(fileSize / chunkSize);// chunk upload functionconst uploadChunk = async (chunkIndex) => { const start = chunkIndex * chunkSize; const end = Math.min((chunkIndex + 1) * chunkSize, fileSize); const formData = new FormData(); formData.append("file", file.slice(start, end)); formData.append("chunkIndex", chunkIndex); formData.append("totalChunks", totalChunks); await axios.post("/upload", formData);};for (let i = 0; i < totalChunks; i++) { await uploadChunk(i);}创建一个名为 DownloadController 的控制器，使用 ApiControllerAttribute 特性声明该控制器为 Web API 控制器。
[ApiController][Route("[controller]")]public class DownloadController : ControllerBase在控制器中实现下面的代码。
using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;using System;using System.IO;namespace ResumeTransfer{ [Route("api/[controller]")] [ApiController] public class DownloadController : ControllerBase { private const string UploadsFolder = "Uploads"; [HttpGet("{ fileName}")] public IActionResult Download(string fileName, long? startByte = null, long? endByte = null) { if (string.IsNullOrEmpty(fileName)) { return BadRequest("Invalid file name"); } string filePath = Path.Combine(Directory.GetCurrentDirectory(), UploadsFolder, fileName); if (!System.IO.File.Exists(filePath)) { return NotFound(); } long contentLength = new System.IO.FileInfo(filePath).Length; // Calculate the range to download. if (startByte == null) { startByte = 0; } if (endByte == null) { endByte = contentLength - 1; } // Adjust the startByte and endByte to be within the range of the file size. if (startByte.Value < 0 || startByte.Value >= contentLength || endByte.Value < startByte.Value || endByte.Value >= contentLength) { Response.Headers.Add("Content-Range", $"bytes */{ contentLength}"); return new StatusCodeResult(416); // Requested range not satisfiable } // Set the Content-Disposition header to enable users to save the file. Response.Headers.Add("Content-Disposition", $"inline; filename={ fileName}"); Response.StatusCode = 206; //Partial Content Response.Headers.Add("Accept-Ranges", "bytes"); long length = endByte.Value - startByte.Value + 1; Response.Headers.Add("Content-Length", length.ToString()); // Send the file data in a range of bytes, if requested byte[] buffer = new byte[1024 * 1024]; using (FileStream stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read)) { stream.Seek(startByte.Value, SeekOrigin.Begin); int bytesRead; while (length > 0 && (bytesRead = stream.Read(buffer, 0, (int)Math.Min(buffer.Length, length))) > 0) { // Check if the client has disconnected. if (!Response.HttpContext.Response.Body.CanWrite) { return Ok(); } Response.Body.WriteAsync(buffer, 0, bytesRead); length -= bytesRead; } } return new EmptyResult(); } }}客户端使用 axios 库进行文件下载。使用下面的代码，将要下载的文件拆分成小块，并按照顺序下载。
const CHUNK_SIZE = 1024 * 1024 * 5; // 5MBconst downloadChunk = async (chunkIndex) => { const res = await axios.get(`/download?fileName=${ fileName}&chunkIndex=${ chunkIndex}`, { responseType: "arraybuffer", }); const arrayBuffer = res.data; const start = chunkIndex * CHUNK_SIZE; const end = start + CHUNK_SIZE; const blob = new Blob([arrayBuffer]); const url = URL.createObjectURL(blob); const a = document.createElement("a"); a.style.display = "none"; a.href = url; a.download = fileName; document.body.appendChild(a); a.click(); URL.revokeObjectURL(url);};for (let i = 0; i < totalChunks; i++) { await downloadChunk(i);}在我们的代码中实现单元测试可以确保代码的正确性，并且可以减少手工测试的负担。我们可以使用
Microsoft.VisualStudio.TestTools.UnitTesting（在 .NET Core 中，也可以使用 xUnit 或 NUnit 进行单元测试）进行单元测试。
下面是一个简单的上传控制器单元测试示例：
using ResumeTransfer;using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;using System.IO;using System.Threading.Tasks;using Xunit;using Microsoft.Extensions.Primitives;using Moq;namespace ResumeTransfer.Tests{ public class UploadControllerTests { [Fact] public async Task Upload_ReturnsBadRequest_WhenNoFileIsSelected() { // Arrange var formCollection = new FormCollection(new Dictionary<string, StringValues>(), new FormFileCollection()); var context = new Mock<HttpContext>(); context.SetupGet(x => x.Request.Form).Returns(formCollection); var controller = new UploadController { ControllerContext = new ControllerContext { HttpContext = context.Object } }; // Act var result = await controller.Upload(null, 0, 1); // Assert Assert.IsType<BadRequestObjectResult>(result); } [Fact] public async Task Upload_ReturnsBadRequest_WhenInvalidChunkIndexOrTotalChunksIsProvided() { // Arrange var fileName = "test.txt"; var fileStream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes("This is a test file.")); var formFile = new FormFile(fileStream, 0, fileStream.Length, "Data", fileName); var formCollection = new FormCollection(new Dictionary<string, StringValues> { { "chunkIndex", "0" }, { "totalChunks", "0" } }, new FormFileCollection { formFile }); var context = new Mock<HttpContext>(); context.SetupGet(x => x.Request.Form).Returns(formCollection); var controller = new UploadController { ControllerContext = new ControllerContext { HttpContext = context.Object } }; // Act var result = await controller.Upload(formFile, 0, 0); // Assert Assert.IsType<BadRequestObjectResult>(result); } [Fact] public async Task Upload_UploadsChunk_WhenChunkDoesNotExist() { // Arrange var fileName = "test.txt"; var fileStream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes("This is a test file.")); var formFile = new FormFile(fileStream, 0, fileStream.Length, "Data", fileName); var formCollection = new FormCollection(new Dictionary<string, StringValues> { { "chunkIndex", "0" }, { "totalChunks", "1" } }, new FormFileCollection { formFile }); var context = new Mock<HttpContext>(); context.SetupGet(x => x.Request.Form).Returns(formCollection); var uploadsFolder = Path.Combine(Directory.GetCurrentDirectory(), "uploads"); var controller = new UploadController { ControllerContext = new ControllerContext { HttpContext = context.Object }, UploadsFolder = uploadsFolder }; // Act var result = await controller.Upload(formFile, 0, 1); var uploadedFilePath = Path.Combine(uploadsFolder, fileName); // Assert Assert.IsType<OkResult>(result); Assert.True(File.Exists(uploadedFilePath)); using (var streamReader = new StreamReader(File.OpenRead(uploadedFilePath))) { var content = await streamReader.ReadToEndAsync(); Assert.Equal("This is a test file.", content); } File.Delete(uploadedFilePath); } [Fact] public async Task Upload_UploadsChunk_WhenChunkExists() { // Arrange var fileName = "test.txt"; var fileStream = new MemoryStream(System.Text.Encoding.UTF8.GetBytes("This is a test file.")); var formFile = new FormFile(fileStream, 0, fileStream.Length, "Data", fileName); var formCollection1 = new FormCollection(new Dictionary<string, StringValues> { { "chunkIndex", "0" }, { "totalChunks", "2" } }, new FormFileCollection { formFile }); var context = new Mock<HttpContext>(); context.SetupGet(x => x.Request.Form).Returns(formCollection1); var uploadsFolder = Path.Combine(Directory.GetCurrentDirectory(), "uploads"); var controller = new UploadController { ControllerContext = new ControllerContext { HttpContext = context.Object }, UploadsFolder = uploadsFolder }; // Act var result1 = await controller.Upload(formFile, 0, 2); // Assert Assert.IsType<OkResult>(result1); // Arrange var formCollection2 = new FormCollection(new Dictionary<string, StringValues> { { "chunkIndex", "1" }, { "totalChunks", "2" } }, new FormFileCollection { formFile }); context.SetupGet(x => x.Request.Form).Returns(formCollection2); // Act var result2 = await controller.Upload(formFile, 1, 2); var uploadedFilePath = Path.Combine(uploadsFolder, fileName); // Assert Assert.IsType<OkResult>(result2); Assert.True(File.Exists(uploadedFilePath)); using (var streamReader = new StreamReader(File.OpenRead(uploadedFilePath))) { var content = await streamReader.ReadToEndAsync(); Assert.Equal("This is a test file.This is a test file.", content); } File.Delete(uploadedFilePath); } }}
为了实现更好的性能和响应时间，我们可以使用 BenchmarkDotNet 进行性能测试，以便找到性能瓶颈并对代码进行优化。
下面是一个简单的上传控制器性能测试示例：
using BenchmarkDotNet.Attributes;using ResumeTransfer;using Microsoft.AspNetCore.Http;using Microsoft.AspNetCore.Mvc;using System.IO;using System.Threading.Tasks;using Microsoft.AspNetCore.Http.Internal;namespace ResumeTransfer.Benchmarks{ [MemoryDiagnoser] public class UploadControllerBenchmarks { private readonly UploadController _controller; private readonly IFormFile _testFile; public UploadControllerBenchmarks() { _controller = new UploadController(); _testFile = new FormFile(new MemoryStream(System.Text.Encoding.UTF8.GetBytes("This is a test file")), 0, 0, "TestFile", "test.txt"); } [Benchmark] public async Task<IActionResult> UploadSingleChunk() { var formCollection = new FormCollection(new System.Collections.Generic.Dictionary<string, Microsoft.Extensions.Primitives.StringValues> { { "chunkIndex", "0" }, { "totalChunks", "1" } }, new FormFileCollection { _testFile }); var request = new DefaultHttpContext(); request.Request.Form = formCollection; _controller.ControllerContext = new ControllerContext { HttpContext = request }; return await _controller.Upload(_testFile, 0, 1); } [Benchmark] public async Task<IActionResult> UploadMultipleChunks() { var chunkSizeBytes = 10485760; // 10 MB var totalFileSizeBytes = 52428800; // 50 MB var totalChunks = (int)Math.Ceiling((double)totalFileSizeBytes / chunkSizeBytes); for (var i = 0; i < totalChunks; i++) { var chunkStartByte = i * chunkSizeBytes; var chunkEndByte = Math.Min(chunkStartByte + chunkSizeBytes - 1, totalFileSizeBytes - 1); var chunkFileContent = new byte[chunkEndByte - chunkStartByte + 1]; using (var memoryStream = new MemoryStream(chunkFileContent)) { using (var binaryWriter = new BinaryWriter(memoryStream)) { binaryWriter.Write(chunkStartByte); binaryWriter.Write(chunkEndByte); } } var chunkFileName = $"{ _testFile.FileName}.part{ i.ToString().PadLeft(5, '0')}"; var chunkFilePath = Path.Combine(Directory.GetCurrentDirectory(), ChunkUploadController.UploadsFolder, chunkFileName); using (var fileStream = new FileStream(chunkFilePath, FileMode.Create, FileAccess.Write, FileShare.Write)) { await fileStream.WriteAsync(chunkFileContent); await fileStream.FlushAsync(); } } var formCollection = new FormCollection(new System.Collections.Generic.Dictionary<string, Microsoft.Extensions.Primitives.StringValues> { { "chunkIndex", "0" }, { "totalChunks", totalChunks.ToString() } }, new FormFileCollection { _testFile }); var request = new DefaultHttpContext(); request.Request.Form = formCollection; _controller.ControllerContext = new ControllerContext { HttpContext = request }; return await _controller.Upload(_testFile, 0, totalChunks); } }}运行上面的代码后，将会输出详细的性能测试结果。
根据测试结果，我们可以找到性能瓶颈，并对代码进行优化，以达到更高的性能和更快的响应时间。
责任编辑：姜华 来源： 今日头条 ASP.NET文件断点上传(责任编辑：百科)
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