Table of Contents
This article focuses on the implementation of HTTP 206 Partial Content
in ASP.NET Web API. I would like to describe how I work on it with ApiController
and deal with some potential performance issues. Our goal is to create a video file streaming service and an HTML5 page to play them.
In my last article, we discussed the characteristic of HTTP 206 and its related headers. Also, we had a showcase of video streaming in Node.js and HTML5. This time, we will move to ASP.NET Web API and will have some discussions regarding our implementation. If you would like to learn more details of this HTTP status code, the last article could be a good reference for you. And we will not repeat it in this article.
First of all, we expect the URL for video streaming shall be like this:
http://localhost/movie/api/media/play?f=praise-our-lord.mp4
where movie
is our application name in IIS, media
is the controller name, play
is its action name and parameter f
represents the video file we would like to play.
Based on this URL, we will start from the MediaController
under the namespace Movie.Controllers
, a class derived from ApiController
. Before we work on its actual action, we need several static
fields and methods to help us in the upcoming steps.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Net.Mime;
using System.Web.Configuration;
using System.Web.Http;
namespace Movie.Controllers
{
public class MediaController : ApiController
{
#region Fields
public const int ReadStreamBufferSize = 1024 * 1024;
public static readonly IReadOnlyDictionary<string, string> MimeNames;
public static readonly IReadOnlyCollection<char> InvalidFileNameChars;
public static readonly string InitialDirectory;
#endregion
#region Constructors
static MediaController()
{
var mimeNames = new Dictionary<string, string>();
mimeNames.Add(".mp3", "audio/mpeg");
mimeNames.Add(".mp4", "video/mp4");
mimeNames.Add(".ogg", "application/ogg");
mimeNames.Add(".ogv", "video/ogg");
mimeNames.Add(".oga", "audio/ogg");
mimeNames.Add(".wav", "audio/x-wav");
mimeNames.Add(".webm", "video/webm");
MimeNames = new ReadOnlyDictionary<string, string>(mimeNames);
InvalidFileNameChars = Array.AsReadOnly(Path.GetInvalidFileNameChars());
InitialDirectory = WebConfigurationManager.AppSettings["InitialDirectory"];
}
#endregion
#region Actions
#endregion
#region Others
private static bool AnyInvalidFileNameChars(string fileName)
{
return InvalidFileNameChars.Intersect(fileName).Any();
}
private static MediaTypeHeaderValue GetMimeNameFromExt(string ext)
{
string value;
if (MimeNames.TryGetValue(ext.ToLowerInvariant(), out value))
return new MediaTypeHeaderValue(value);
else
return new MediaTypeHeaderValue(MediaTypeNames.Application.Octet);
}
private static bool TryReadRangeItem(RangeItemHeaderValue range, long contentLength,
out long start, out long end)
{
if (range.From != null)
{
start = range.From.Value;
if (range.To != null)
end = range.To.Value;
else
end = contentLength - 1;
}
else
{
end = contentLength - 1;
if (range.To != null)
start = contentLength - range.To.Value;
else
start = 0;
}
return (start < contentLength && end < contentLength);
}
private static void CreatePartialContent(Stream inputStream, Stream outputStream,
long start, long end)
{
int count = 0;
long remainingBytes = end - start + 1;
long position = start;
byte[] buffer = new byte[ReadStreamBufferSize];
inputStream.Position = start;
do
{
try
{
if (remainingBytes > ReadStreamBufferSize)
count = inputStream.Read(buffer, 0, ReadStreamBufferSize);
else
count = inputStream.Read(buffer, 0, (int)remainingBytes);
outputStream.Write(buffer, 0, count);
}
catch (Exception error)
{
Debug.WriteLine(error);
break;
}
position = inputStream.Position;
remainingBytes = end - position + 1;
} while (position <= end);
}
#endregion
}
}
And we have:
AnyInvalidFileNameChars()
helps us to check if there is any invalid file name character in URL parameter f
(by the way, this is a good example of using LINQ on string
). This can prevent some unnecessary file system accesses because a file with invalid file name won't exist at all. GetMimeNameFromExt()
helps us to get the corresponding Content-Type
header value with file extension from the read-only dictionary MimeNames
. If value cannot be found, the default one is application/oct-stream
. TryReadRangeItem()
helps us to read Range
header from current HTTP request. Returned boolean value represents if range is available. If start or end position is greater than file length (parameter contentLength
), it returns false
. CreatePartialContent()
helps us to copy content from file stream to response stream with indicated range.
With these tools, to implement the action Play()
method will be much easier. The prototype is:
[HttpGet]
public HttpResponseMessage Play(string f) { }
where parameter f
represents the URL parameter f
. HttpGetAttribute
declares that GET
is the only acceptable HTTP method. The response headers and content are sent in HttpResponseMessage
class. The logic flow behind this method can be described with the following chart.
Naturally, our first job is to see if the file exists. If not, it will result in HTTP 404 Not Found
status. Next is to check if Range
header is present in current request. If not, the request will be treated as normal request and will result in HTTP 200 OK
status. The third step is to determine if Range
header can be fulfilled according to target file. If range is not present within file length, HTTP 416 Requested Range Not Satisfiable
status will be responded to browser. After these steps, last one is to transmit target file with indicated range, and the story ends with HTTP 206 Partial Content
status.
Here is the complete code of Play()
action.
[HttpGet]
public HttpResponseMessage Play(string f)
{
if (string.IsNullOrWhiteSpace(f) || AnyInvalidFileNameChars(f))
throw new HttpResponseException(HttpStatusCode.NotFound);
FileInfo fileInfo = new FileInfo(Path.Combine(InitialDirectory, f));
if (!fileInfo.Exists)
throw new HttpResponseException(HttpStatusCode.NotFound);
long totalLength = fileInfo.Length;
RangeHeaderValue rangeHeader = base.Request.Headers.Range;
HttpResponseMessage response = new HttpResponseMessage();
response.Headers.AcceptRanges.Add("bytes");
if (rangeHeader == null || !rangeHeader.Ranges.Any())
{
response.StatusCode = HttpStatusCode.OK;
response.Content = new PushStreamContent((outputStream, httpContent, transpContext)
=>
{
using (outputStream)
using (Stream inputStream = fileInfo.OpenRead())
{
try
{
inputStream.CopyTo(outputStream, ReadStreamBufferSize);
}
catch (Exception error)
{
Debug.WriteLine(error);
}
}
}, GetMimeNameFromExt(fileInfo.Extension));
response.Content.Headers.ContentLength = totalLength;
return response;
}
long start = 0, end = 0;
if (rangeHeader.Unit != "bytes" || rangeHeader.Ranges.Count > 1 ||
!TryReadRangeItem(rangeHeader.Ranges.First(), totalLength, out start, out end))
{
response.StatusCode = HttpStatusCode.RequestedRangeNotSatisfiable;
response.Content = new StreamContent(Stream.Null);
response.Content.Headers.ContentRange = new ContentRangeHeaderValue(totalLength);
response.Content.Headers.ContentType = GetMimeNameFromExt(fileInfo.Extension);
return response;
}
var contentRange = new ContentRangeHeaderValue(start, end, totalLength);
response.StatusCode = HttpStatusCode.PartialContent;
response.Content = new PushStreamContent((outputStream, httpContent, transpContext)
=>
{
using (outputStream)
using (Stream inputStream = fileInfo.OpenRead())
CreatePartialContent(inputStream, outputStream, start, end);
}, GetMimeNameFromExt(fileInfo.Extension));
response.Content.Headers.ContentLength = end - start + 1;
response.Content.Headers.ContentRange = contentRange;
return response;
}
Now it is time to play the video. We have a simple HTML5 page with a <video />
element and a <source />
element referring to the URL we have mentioned before.
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function onLoad() {
var sec = parseInt(document.location.search.substr(1));
if (!isNaN(sec))
mainPlayer.currentTime = sec;
}
</script>
<title>Partial Content Demonstration</title>
</head>
<body>
<h3>Partial Content Demonstration</h3>
<hr />
<video id="mainPlayer" width="640" height="360"
autoplay="autoplay" controls="controls" onloadeddata="onLoad()">
<source src="api/media/play?f=praise-our-lord.mp4" />
</video>
</body>
</html>
As you can see, the onLoad()
function allows us skipping to indicated second by adding parameter. If parameter is omitted, the <video />
element plays the video from zero. For example, if we want to watch the video starting from 120th second, then we have:
http://localhost/movie/index.html?120
Let us try this URL in Chrome.
Then we press F12 to open the development tool, switch to Network tab to see what happened behind the scenes.
These headers explain almost everything. Once onLoad()
function gets triggered, the player sends a request including a Range
header and the start position is exactly equal to the byte position of 120th second in this video. And the response header Content-Range
describes start and end position, and total available bytes. This example shows the biggest benefit of Partial Content mechanism: when a video or audio file is too long, viewers can skip to any second they want.
You have probably noticed that we are using PushStreamContent
instead of StreamContent
in Play()
action (excepting empty content) to transfer file stream. Both of them are under the namespace System.Net.Http
and derived from HttpContent
class. The differences between them could be generally summarized as following points.
PushStreamContent vs. StreamContent
- Sequence - For
StreamContent
, you have to generate content stream before action ends. For PushStreamContent
, you will generate it after exit from the action. - File Access - For
StreamContent
, you generate content stream from file before browser starts receiving. For PushStreamContent
, you will do it after browser has received all HTTP headers and is ready to render content, which means if browser receives headers only but cancels rendering content, the file will not be opened. - Memory Usage - For
StreamContent
, you have to generate partial content stream from file before action ends, which means it will be kept in memory temporarily until browser has received its all bytes. For PushStreamContent
, you can directly copy content from file to outgoing stream with specified range and without keeping content temporarily in memory.
Therefore, we choose PushStreamContent
for video file streaming. It could reduce memory usage and work more efficiently.
2014-11-25
- Fixed a potential issue in
CreatePartialContent()
method when file size is greater than Int32.MaxValue
. - Added
try
-catch
section in Play()
method to prevent unnecessary exception message in debug mode. - Increased
ReadStreamBufferSize
value to improve performance.