Netcore WebApi中支持Range返回视频

背景

业务需要，通过WebApi返回视频，起初，直接在Controller读取视频信息，返回FileContentResult。大部分浏览器也能正常播放。但是会存在以下问题：

• Mac系统下safari浏览器播放视频失败。
• Html Video标签下，视频无法拖动进度，一些类似进度跳转，加载到最近一次播放进度的功能需求就无法满足。
• 视频加载缓慢，wpf或其他客户端下，一些大视频可能会加载很长时间才能播放，而且播放卡顿严重。

原因

Mac 系统Safari浏览器在加载视频是要求视频必须支持分块加载，即必须支持Range请求头，而我们直接返回FileContentResult是不支持Range的。
同样，Video标签下不能拖动进度和客户端加载视频缓慢也是这个原因。

解决

找到原因，解决问题就相对简单了，google了一番，加上GitHub搜索，找到如下方法。废话不多说，直接上代码。

VideoStreamResult类

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Net.Http.Headers;
using System;
using System.IO;
using System.Linq;
using System.Net;
using System.Threading.Tasks;

public class VideoStreamResult : FileStreamResult
{
    // default buffer size as defined in BufferedStream type
    private const int BufferSize = 0x1000;
    private string MultipartBoundary = "<qwe123>";

    public VideoStreamResult(Stream fileStream, string contentType)
        : base(fileStream, contentType)
    {

    }

    public VideoStreamResult(Stream fileStream, MediaTypeHeaderValue contentType)
        : base(fileStream, contentType)
    {

    }

    private bool IsMultipartRequest(RangeHeaderValue range)
    {
        return range != null && range.Ranges != null && range.Ranges.Count > 1;
    }

    private bool IsRangeRequest(RangeHeaderValue range)
    {
        return range != null && range.Ranges != null && range.Ranges.Count > 0;
    }

    protected async Task WriteVideoAsync(HttpResponse response)
    {
        var bufferingFeature = response.HttpContext.Features.Get<IHttpResponseBodyFeature>();
        bufferingFeature?.DisableBuffering();

        var length = FileStream.Length;

        var range = response.HttpContext.GetRanges(length);

        if (IsMultipartRequest(range))
        {
            response.ContentType = $"multipart/byteranges; boundary={MultipartBoundary}";
        }
        else
        {
            response.ContentType = ContentType.ToString();
        }

        response.Headers.Add("Accept-Ranges", "bytes");

        if (IsRangeRequest(range))
        {
            response.StatusCode = (int)HttpStatusCode.PartialContent;

            if (!IsMultipartRequest(range))
            {
                response.Headers.Add("Content-Range", $"bytes {range.Ranges.First().From}-{range.Ranges.First().To}/{length}");
            }

            foreach (var rangeValue in range.Ranges)
            {
                if (IsMultipartRequest(range)) // dunno if multipart works
                {
                    await response.WriteAsync($"--{MultipartBoundary}");
                    await response.WriteAsync(Environment.NewLine);
                    await response.WriteAsync($"Content-type: {ContentType}");
                    await response.WriteAsync(Environment.NewLine);
                    await response.WriteAsync($"Content-Range: bytes {range.Ranges.First().From}-{range.Ranges.First().To}/{length}");
                    await response.WriteAsync(Environment.NewLine);
                }

                await WriteDataToResponseBody(rangeValue, response);

                if (IsMultipartRequest(range))
                {
                    await response.WriteAsync(Environment.NewLine);
                }
            }

            if (IsMultipartRequest(range))
            {
                await response.WriteAsync($"--{MultipartBoundary}--");
                await response.WriteAsync(Environment.NewLine);
            }
        }
        else
        {
            await FileStream.CopyToAsync(response.Body);
        }
    }

    private async Task WriteDataToResponseBody(RangeItemHeaderValue rangeValue, HttpResponse response)
    {
        var startIndex = rangeValue.From ?? 0;
        var endIndex = rangeValue.To ?? 0;

        byte[] buffer = new byte[BufferSize];
        long totalToSend = endIndex - startIndex;
        int count = 0;

        long bytesRemaining = totalToSend + 1;
        response.ContentLength = bytesRemaining;

        FileStream.Seek(startIndex, SeekOrigin.Begin);

        while (bytesRemaining > 0)
        {
            try
            {
                if (bytesRemaining <= buffer.Length)
                    count = FileStream.Read(buffer, 0, (int)bytesRemaining);
                else
                    count = FileStream.Read(buffer, 0, buffer.Length);

                if (count == 0)
                    return;

                await response.Body.WriteAsync(buffer, 0, count);

                bytesRemaining -= count;
            }
            catch (IndexOutOfRangeException)
            {
                await response.Body.FlushAsync();
                return;
            }
            finally
            {
                await response.Body.FlushAsync();
            }
        }
    }

    public override async Task ExecuteResultAsync(ActionContext context)
    {
        await WriteVideoAsync(context.HttpContext.Response);
    }
}

这里使用了一个扩展方法：

public static RangeHeaderValue GetRanges(this HttpContext context, long contentSize)
{
    RangeHeaderValue rangesResult = null;

    string rangeHeader = context.Request.Headers["Range"];

    if (!string.IsNullOrEmpty(rangeHeader))
    {
        string[] ranges = rangeHeader.Replace("bytes=", string.Empty).Split(",".ToCharArray());

        rangesResult = new RangeHeaderValue();

        for (int i = 0; i < ranges.Length; i++)
        {
            const int START = 0, END = 1;

            long endByte, startByte;

            long parsedValue;

            string[] currentRange = ranges[i].Split("-".ToCharArray());

            if (long.TryParse(currentRange[END], out parsedValue))
                endByte = parsedValue;
            else
                endByte = contentSize - 1;


            if (long.TryParse(currentRange[START], out parsedValue))
                startByte = parsedValue;
            else
            {
                startByte = contentSize - endByte;
                endByte = contentSize - 1;
            }

            rangesResult.Ranges.Add(new RangeItemHeaderValue(startByte, endByte));
        }
    }

    return rangesResult;
}

在Controller中使用：

public async Task<ActionResult> DownloadById(string filepath)
{
    ///根据业务，获取文件Stream
    var stream = new FileStream(filepath, FileMode.Open, FileAccess.Read);
    return new VideoStreamResult(stream, mimeType);
}