源码如下：
/// <summary>/// 文件处理/// </summary>[RoutePrefix("api/fs")]public class FileStoreController : ApiController{/// <summary>/// 文件预览/// </summary>/// <param name="filepath">文件路径</param>/// <returns></returns>[Description("文件预览")][HttpGet, Route("preview")]public HttpResponseMessage Preview([Description("文件路径")] string filepath){try{FileInfo fileInfo = new FileInfo(filepath);long fileSize = fileInfo.Length;var response = Request.CreateResponse();StreamContent content = null;// 下载的字节范围long startByte = 0, endByte = fileSize - 1, totalByte = fileSize;if (Request.Headers.TryGetValues("range", out IEnumerable<string> rangeHeader)){// 断点续传var rangeString = rangeHeader.FirstOrDefault();var match = Regex.Match(rangeString, @"bytes=(\d+)-(\d+)");// 文件总大小totalByte = fileSize;startByte = long.Parse(match.Groups[1].Value);endByte = long.Parse(match.Groups[2].Value);// 返回http状态response.StatusCode = HttpStatusCode.PartialContent;long bytesToRead = endByte - startByte + 1;var contentStream = ReadFileInRange(filepath, startByte, endByte);content = new StreamContent(contentStream);content.Headers.ContentLength = Convert.ToInt32(endByte - startByte + 1);}else{// 文件总大小totalByte = fileSize;// 下载起始位置startByte = 0;// 下载结束位置endByte = totalByte - 1;response.StatusCode = HttpStatusCode.OK;using (var ms = new MemoryStream()){content = new StreamContent(ms);}}//表明服务器支持分片加载response.Headers.AcceptRanges.Add("bytes");//Content - Range: bytes 0 - 65535 / 408244，表明此次返回的文件范围content.Headers.ContentRange = new ContentRangeHeaderValue(startByte, endByte, totalByte);告知浏览器这是一个字节流，浏览器处理字节流的默认方式就是下载content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");response.Content = content;//需要设置此属性，否则浏览器默认不会读取到响应头中的Accept-Ranges属性，因此会认为服务器端不支持分片，所以会直接全文下载response.Headers.Add("Access-Control-Expose-Headers", "*");response.Headers.Add("Access-Control-Allow-Headers", "range,Accept-Ranges,Content-Range,Content-Type,X-CAF-Authorization-Token,sessionToken,X-TOKEN,Cache-Control,If-Modified-Since");return response;}catch (Exception ex){return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, "服务器内部异常");}}private static MemoryStream ReadFileInRange(string filePath, long startByte, long endByte){// 验证参数if (startByte < 0 || endByte < startByte){throw new ArgumentException("Invalid byte range");}try{using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read)){// 计算要读取的字节数long bytesToRead = endByte - startByte + 1;// 创建缓冲区byte[] buffer = new byte[bytesToRead];// 将文件流的位置设置为开始字节fileStream.Seek(startByte, SeekOrigin.Begin);// 读取字节到缓冲区fileStream.Read(buffer, 0, (int)bytesToRead);// 创建一个MemoryStream来存储读取的字节MemoryStream resultStream = new MemoryStream(buffer);return resultStream;}}catch (Exception ex){// 在这里处理任何异常，比如文件未找到或读取错误Console.WriteLine("Error: " + ex.Message);return null;}}源代码github地址：
https://github.com/LeoMingGit/dotNetPractiseCollect/blob/master/%E5%88%86%E7%89%87%E9%A2%84%E8%A7%88pdf/FileStoreController.cs
