HTTP协议中的压缩
Http协议中使用Accept-Encoding和Content-Encoding头来表示期望Response内容的编码和当前Request的内容编码。而Http内容的压缩其实是内容编码的子集。所以也通过这两个头来描述Http Request和Response内容的压缩方式。
常用的压缩算法有gzip(采用GNU zip压缩)和deflate(采用zlib的格式压缩)，对应的Http头中的值也为：gzip或者deflate.
内容压缩与解压
Web服务器可以配置进行全局压缩和解压。当压缩或者解压需要基于某些逻辑进行判断，则要自行实现。
浏览器（或者部分移动端网络库，包括iOS系统网络库）会对Content-Encoding头的值设为gzip或deflate的Response自动解压。而压缩则需要自己实现。
实现
这里采用DotNetZip库进行压缩和解压。
首先创建两个压缩类来分别对gzip和deflate进行处理：
public abstract class Compressor
{
public abstract byte[] Compress(byte[] originalData); public abstract byte[] Decompress(byte[] compressedData);
} public class DeflateCompressor : Compressor
{
public static string Name => "Deflate"; public override byte[] Compress(byte[] originalData)
{
using (var outputStream = new MemoryStream())
{
using (var gzipStream = new DeflateStream(outputStream, CompressionMode.Compress, CompressionLevel.BestSpeed))
{
gzipStream.Write(originalData, , originalData.Length);
} return outputStream.ToArray();
}
} public override byte[] Decompress(byte[] compressedData)
{
using (var inputStream = new MemoryStream(compressedData))
{
var outputStream = new MemoryStream();
var gzipStream = new DeflateStream(inputStream, CompressionMode.Decompress, CompressionLevel.BestSpeed);
int blockSize = * ;
int readSize = ;
while (readSize > )
{
byte[] buffer = new byte[blockSize];
readSize = gzipStream.Read(buffer, , blockSize);
if (readSize > )
{
outputStream.Write(buffer, , readSize);
}
} outputStream.Flush();
return outputStream.ToArray();
}
}
}
public class GZipCompressor : Compressor
{
public static string Name => "GZip"; public override byte[] Compress(byte[] originalData)
{
using (var outputStream = new MemoryStream())
{
using (var gzipStream = new GZipStream(outputStream, CompressionMode.Compress, CompressionLevel.BestSpeed))
{
gzipStream.Write(originalData, , originalData.Length);
} return outputStream.ToArray();
}
} public override byte[] Decompress(byte[] compressedData)
{
using (var inputStream = new MemoryStream(compressedData))
{
var outputStream = new MemoryStream();
var gzipStream = new GZipStream(inputStream, CompressionMode.Decompress, CompressionLevel.BestSpeed);
int blockSize = * ;
int readSize = ;
while (readSize > )
{
byte[] buffer = new byte[blockSize];
readSize = gzipStream.Read(buffer, , blockSize);
if (readSize > )
{
outputStream.Write(buffer, , readSize);
}
} outputStream.Flush();
return outputStream.ToArray();
}
}
}
创建一个DelegatingHandler: CompressHandler
public class CompressHandler : DelegatingHandler
{
private Dictionary<string, Compressor> _supportCompressors = new Dictionary<string, Compressor>(); public void RegisterCompressor(string compressorName, Compressor compressor)
{
if (string.IsNullOrEmpty(compressorName) || compressor == null)
{
throw new InvalidOperationException("parameter is invalid.");
} _supportCompressors[compressorName.ToLower()] = compressor;
} public CompressHandler()
{ } protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
//拦截请求，对请求进行解压
await DecompressRequestIfNeed(request);
var response = await base.SendAsync(request, cancellationToken);
//对响应进行压缩
await CompressResponseIfNeed(request, response); return response;
} private async Task DecompressRequestIfNeed(HttpRequestMessage request)
{
if (request.Content != null)
{
var originalContentType = request.Content.Headers.ContentType;
foreach (var encoding in request.Content.Headers.ContentEncoding)
{
if (_supportCompressors.ContainsKey(encoding))
{
var compressor = _supportCompressors[encoding];
var compressedBytes = await request.Content.ReadAsByteArrayAsync();
if (compressedBytes == null || compressedBytes.Length == )
{
// don't need to decompress, since the content is empty.
break;
} //基于Content-Encoding进行解压
var decompressedBytes = compressor.Decompress(compressedBytes);
var byteContent = new ByteArrayContent(decompressedBytes);
request.Content = byteContent;
//恢复原始的ContentTypeHeader到新的RequestContent中
request.Content.Headers.ContentType = originalContentType; break;
}
}
}
} private async Task CompressResponseIfNeed(HttpRequestMessage request, HttpResponseMessage response)
{
if (response.Content != null)
{
foreach (var acceptEncoding in request.Headers.AcceptEncoding)
{
if (_supportCompressors.ContainsKey(acceptEncoding.Value.ToLower()))
{
var originalBytes = await response.Content.ReadAsByteArrayAsync();
if (originalBytes == null || originalBytes.Length == )
{
// don't need to compress, since the content is empty.
break;
}
//基于客户端能接受的压缩算法进行压缩
var compressor = _supportCompressors[acceptEncoding.Value];
var compresedBytes = compressor.Compress(originalBytes);
//重新设置新的Response Content和Header
response.Content = new ByteArrayContent(compresedBytes);
response.Content.Headers.ContentEncoding.Add(acceptEncoding.Value);
response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json"); break;
}
}
}
}
}
将CompressHandler添加到WebApi的MessageHandler列表中来拦截Http请求和响应， 来执行压缩和解压。
public static void Register(HttpConfiguration config)
{ var compressHandler = new CompressHandler();
//将GZip和Deflate压缩器注册到CompressHandler
compressHandler.RegisterCompressor(GZipCompressor.Name, new GZipCompressor());
compressHandler.RegisterCompressor(DeflateCompressor.Name, new DeflateCompressor());
config.MessageHandlers.Add(compressHandler);
config.MapHttpAttributeRoutes();
}