一. HTTP gzip压缩,概述

• request
• header 中声明 Accept-Encoding : gzip，告知服务器客户端接受gzip的数据
• response
• body，同时加入以下header： Content-Encoding : gzip：表明body是gzip过的数据
• Content-Length:117 ：表示body gzip压缩后的数据大小，便于客户端使用
• 或 Transfer-Encoding: chunked ：分块传输编码

二. 如何使用gzip进行压缩

tomcat 开启压缩（gzip）

tomcat server.xml

 <Connector
compression="on" # 表示开启压缩
noCompressionUserAgents="gozilla, traviata"
 compress ionMinSize="2048" # 表示会对大于2KB的文件进行压缩
compressableMimeType="text/html,text/xml,text/css,text/javascript,image/gif,image/jpg" # 是指将进行压缩的文件类型
/>  

• 弊端
  对HTTP传输内容进行压缩是改良前端响应性能的可用方法之一，大型网站都在用。但是也有缺点，就是压缩过程占用cpu的资源，客户端浏览器解析也占据了一部分时间。但是随着硬件性能不断的提高，这些问题正在不断的弱化。

程序压缩/解压

GZIP input Stream(解压) / GZIPOutputStream(压缩)

• netflix.zuul相关示例

 # org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter#writeResponse()
is = context.getResponseDataStream();
 inputStream  inputStream = is;
 if  (is != null) {
if (context.sendZuulResponse()) {
// if origin response is gzipped, and client has not requested gzip,
// decompress stream
// before sending to client
// else, stream gzip directly to client
if (context.getResponseGZipped() && !isGzip Request ed) {
// If origin tell it's GZipped but the content is ZERO bytes,
// don't try to uncompress
final Long len = context.getOriginContentLength();
if (len == null || len > 0) {
try {
inputStream = new GZIPInputStream(is);
}catch ( java .util.zip.Zip Exception  ex) {
log.debug("gzip expected but not "+ "received assuming unencoded response "+ RequestContext.getCurrentContext()
.getRequest().getRequestURL()
. toString ());
inputStream = is;
}
}else {
// Already done : inputStream = is;
}
}else if (context.getResponseGZipped() && isGzipRequested) {
servletResponse.setHeader(ZuulHeaders.CONTENT_ENCODING, "gzip");
}
writeResponse(inputStream, outStream);
}
}

# com.netflix.zuul.http.HttpServletRequestWrapper.UnitTest#handlesGzipRequestBody
@Test
public  void  handlesGzipRequestBody() throws IOException {
// creates string, gzips into  byte  array which will be mocked as InputStream of request
final String body = "hello";
final byte[] bodyBytes = body.getBytes();
// in this case the compressed stream is actually larger - need to allocate enough space
final ByteArrayOutputStream byteOutStream = new ByteArrayOutputStream(0);
final GZIPOutputStream gzipOutStream = new GZIPOutputStream(byteOutStream);
gzipOutStream.write(bodyBytes);
gzipOutStream.finish();
gzipOutStream.flush();
body(byteOutStream.toByteArray());

final HttpServletRequestWrapper wrapper = new HttpServletRequestWrapper(request);
assertEquals(body, IOUtils.toString(new GZIPInputStream(wrapper.getInputStream())));
}  

示例: 网关主动对response进行压缩响应(可减少带宽) GZIPOutputStream

• 简单实现示例.实际情况需考虑更新情况,如是否已经被压缩等

 InputStream inputStream = okResponse.body().byteStream();
try {
// 网关主动对response进行压缩响应(可减少带宽)
HttpServletRequest request = RequestContext.getCurrentContext().getRequest();
 Boolean  isGatewayGZIP = Boolean.parseBoolean(request.getHeader("x-gateway-gzip"));
if (!isGatewayGZIP) {
isGatewayGZIP = Boolean.parseBoolean(request.getParameter("x-gateway-gzip"));
}

if (isGatewayGZIP) {
final ByteArrayOutputStream byteOutStream = new ByteArrayOutputStream(0);
final GZIPOutputStream gzipOutStream = new GZIPOutputStream(byteOutStream);
g zip OutStream.write(okResponse.body().bytes());
gzipOutStream.finish();
gzipOutStream.flush();
inputStream = new ServletInputStreamWrapper(byteOutStream.toByteArray());
httpHeaders.add(ZuulHeaders.CONTENT_ENCODING, "gzip");
}
} catch (Exception e) {
logger.error("GatewayGZIP error:", e);
}  

三.okhttp 压缩相关处理

okHttp 解压gzip,条件: Content-Encoding = gizp

• okio.GzipSource

 if (transparentGzip
&& "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
&& HttpHeaders.hasBody(networkResponse)) {
GzipSource responseBody = new GzipSource(networkResponse.body().source());
Headers strippedHeaders = networkResponse.headers().newBuilder()
.removeAll("Content-Encoding")
.removeAll("Content-Length")
.build();
responseBuilder.headers(strippedHeaders);
String contentType = networkResponse.header("Content-Type");
responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
}  

okhttp gzip压缩/解压 (示例)

 //zip压缩
GzipSink gzipSink = new GzipSink(Okio.sink( file ));
BufferedSink bufferedSink = Okio.buffer(gzipSink);
bufferedSink.writeUtf8("this is zip file");
bufferedSink.flush();
bufferedSink.close();

//读取zip
GzipSource gzipSource = new GzipSource(Okio.source(file));
BufferedSource bufferedSource = Okio.buffer(gzipSource);
String s = bufferedSource.readUtf8();  

okhttp框架－如何 对请求(request)数据进行GZIP压缩 – GzipRequestInterceptor

 OkHttpClient okHttpClient = new OkHttpClient.Builder() 
.addInterceptor(new GzipRequestInterceptor())//开启Gzip压缩
...
.build();
GzipRequestInterceptor
#issuecomment-123105641
class GzipRequestInterceptor implements Interceptor {
@Override 
public Response intercept(Chain chain) throws IOException {
Request originalRequest = chain.request();
if (originalRequest.body() == null || originalRequest.header("Content-Encoding") != null) {
return chain.proceed(originalRequest);
}

Request compressedRequest = originalRequest.newBuilder()
.header("Content-Encoding", "gzip")
.method(originalRequest.method(), forceContentLength(gzip(originalRequest.body())))
.build();
return chain.proceed(compressedRequest);
}

/**  */ private  RequestBody forceContentLength(final RequestBody requestBody) throws IOException {
      final Buffer buffer = new Buffer();
      requestBody.writeTo(buffer);
      return new RequestBody() {
        @Override
        public MediaType contentType() {
              return requestBody.contentType();
        }

        @Override
        public long contentLength() {
              return buffer.size();
        }

      @Override
      public void writeTo(BufferedSink sink) throws IOException {
            sink.write(buffer.snapshot());
      }
};
}

private RequestBody gzip(final RequestBody body) {
return new RequestBody() {
      @Override 
        public MediaType contentType() {
            return body.contentType();
      }

      @Override 
       public long contentLength() {
            return -1; // We don't know the compressed length in advance!
      }

      @Override 
       public void writeTo(BufferedSink sink) throws IOException {
            BufferedSink gzipSink = Okio.buffer(new GzipSink(sink));
            body.writeTo(gzipSink);
            gzipSink.close();
      }
};
}
}  

okhttp框架－如何对请求数据进行GZIP压缩

Okhttp3请求网络开启Gzip压缩 – CSDN 博客

四. Nginx 的Gzip可以对服务器端响应内容进行压缩从而减少一定的客户端响应时间

 gzip on;
gzip_min_length 1k;
gzip_buffers 4 32k;
gzip_types text/plain application/x-javascript application/javascript text/xml text/css;
gzip_vary on;  

API网关那些儿 | I’m Yunlong

 source: //liuxiang.github.io/2018/08/13/HTTP%20gzip压缩