关于这个类就不做过多介绍了，比较简单。ResponseCompressionProvider是我们提供响应压缩算法的核心类，具体如何自动选用压缩算法都是由它提供的。这个类中的代码比较多，我们就不逐个方法讲解了，具体源码可自行查阅[点击查看源码👈]，首先我们先看ResponseCompressionProvider的构造函数
public ResponseCompressionProvider(IServiceProvider services, IOptions<ResponseCompressionOptions> options) { var responseCompressionOptions = options.Value; _providers = responseCompressionOptions.Providers.ToArray(); //如果没有设置压缩类型默认采用Br和Gzip压缩算法 if (_providers.Length == 0) { _providers = new ICompressionProvider[] { new CompressionProviderFactory(typeof(BrotliCompressionProvider)), new CompressionProviderFactory(typeof(GzipCompressionProvider)), }; } //根据CompressionProviderFactory创建对应的压缩算法Provider比如GzipCompressionProvider for (var i = 0; i < _providers.Length; i++) { var factory = _providers[i] as CompressionProviderFactory; if (factory != null) { _providers[i] = factory.CreateInstance(services); } } //设置默认的压缩目标类型默认为text/plain、text/css、text/html、application/javascript、application/xml //text/xml、application/json、text/json、application/was var mimeTypes = responseCompressionOptions.MimeTypes; if (mimeTypes == null || !mimeTypes.Any()) { mimeTypes = ResponseCompressionDefaults.MimeTypes; } //将默认MimeType放入HashSet _mimeTypes = new HashSet<string>(mimeTypes, StringComparer.OrdinalIgnoreCase); _excludedMimeTypes = new HashSet<string>( responseCompressionOptions.ExcludedMimeTypes ?? Enumerable.Empty<string>(), StringComparer.OrdinalIgnoreCase ); _enableForHttps = responseCompressionOptions.EnableForHttps; }
其中BrotliCompressionProvider、GzipCompressionProvider是具体提供压缩方法的地方，咱们就看比较常用的Gzip的Provider的大致实现[点击查看源码👈]
public class GzipCompressionProvider : ICompressionProvider { public GzipCompressionProvider(IOptions<GzipCompressionProviderOptions> options) { Options = options.Value; } private GzipCompressionProviderOptions Options { get; } // 对应的Encoding名称 public string EncodingName { get; } = "gzip"; public bool SupportsFlush => true; // 核心代码就是这句 将原始的输出流转换为压缩的GZipStream // 我们设置的Level压缩级别将决定压缩的性能和质量 public Stream CreateStream(Stream outputStream) => new GZipStream(outputStream, Options.Level, leaveOpen: true); }
关于ResponseCompressionProvider其他相关的方法咱们在讲解UseResponseCompression中间件的时候在具体看用到的方法，因为这个类是响应压缩的核心类，现在提前说了，到中间件使用的地方可能会忘记了。接下来我们就看UseResponseCompression的大致实现。
UseResponseCompression#
UseResponseCompression具体也就一个无参的扩展方法，也比较简单，因为配置和工作都由注入的地方完成了，所以我们直接查看中间件里的实现，找到中间件位置ResponseCompressionMiddleware[点击查看源码👈]
public class ResponseCompressionMiddleware { private readonly RequestDelegate _next; private readonly IResponseCompressionProvider _provider; public ResponseCompressionMiddleware(RequestDelegate next, IResponseCompressionProvider provider) { _next = next; _provider = provider; } public async Task Invoke(HttpContext context) { //判断是否包含Accept-Encoding头信息，不包含直接大喊一声"抬走下一个" if (!_provider.CheckRequestAcceptsCompression(context)) { await _next(context); return; } //获取原始输出Body var originalBodyFeature = context.Features.Get<IHttpResponseBodyFeature>(); var originalCompressionFeature = context.Features.Get<IHttpsCompressionFeature>(); //初始化响应压缩Body var compressionBody = new ResponseCompressionBody(context, _provider, originalBodyFeature); //设置成压缩Body context.Features.Set<IHttpResponseBodyFeature>(compressionBody); context.Features.Set<IHttpsCompressionFeature>(compressionBody); try { await _next(context); await compressionBody.FinishCompressionAsync(); } finally { //恢复原始Body context.Features.Set(originalBodyFeature); context.Features.Set(originalCompressionFeature); } } }