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"
		compressionMinSize="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

GZIPInputStream(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() && !isGzipRequested) {
						// 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.ZipException 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);
		gzipOutStream.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
https://github.com/square/okhttp\issues/350#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);
}

/** https://github.com/square/okhttp\issues/350 */
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

https://cloud.tencent.com/info/61307ab74137a46628c2ea2ca42a6eb4.html

Okhttp3请求网络开启Gzip压缩 - CSDN博客

https://blog.csdn.net/aiynmimi/article/details/77453809

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

http://ylzheng.com/2017/03/14/the-things-about-api-gateway

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