源码

@Override public Response intercept(Chain chain) throws IOException {
 Request userRequest = chain.request();
 Request.Builder requestBuilder = userRequest.newBuilder();

 RequestBody body = userRequest.body();
 if (body != null) {
   MediaType contentType = body.contentType();
   if (contentType != null) {
     requestBuilder.header("Content-Type", contentType.toString());
   }

   long contentLength = body.contentLength();
   if (contentLength != -1) {
     requestBuilder.header("Content-Length", Long.toString(contentLength));
     requestBuilder.removeHeader("Transfer-Encoding");
   } else {
     requestBuilder.header("Transfer-Encoding", "chunked");
     requestBuilder.removeHeader("Content-Length");
   }
 }

 if (userRequest.header("Host") == null) {
   requestBuilder.header("Host", hostHeader(userRequest.url(), false));
 }

 if (userRequest.header("Connection") == null) {
   requestBuilder.header("Connection", "Keep-Alive");
 }

 // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
 // the transfer stream.
 boolean transparentGzip = false;
 if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
   transparentGzip = true;
   requestBuilder.header("Accept-Encoding", "gzip");
 }

 List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
 if (!cookies.isEmpty()) {
   requestBuilder.header("Cookie", cookieHeader(cookies));
 }

 if (userRequest.header("User-Agent") == null) {
   requestBuilder.header("User-Agent", Version.userAgent());
 }

 Response networkResponse = chain.proceed(requestBuilder.build());

 HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

 Response.Builder responseBuilder = networkResponse.newBuilder()
     .request(userRequest);

 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)));
 }

 return responseBuilder.build();
}

/** Returns a 'Cookie' HTTP request header with all cookies, like {@code a=b; c=d}. */
private String cookieHeader(List<Cookie> cookies) {
 StringBuilder cookieHeader = new StringBuilder();
 for (int i = 0, size = cookies.size(); i < size; i++) {
   if (i > 0) {
     cookieHeader.append("; ");
   }
   Cookie cookie = cookies.get(i);
   cookieHeader.append(cookie.name()).append('=').append(cookie.value());
 }
 return cookieHeader.toString();
}

报文头

添加请求头
Cookie管理
Gzip压缩

常见的HTTP报文头属性

Accpet

告诉服务端,客户端接收什么类型的响应
Referer

表示这是请求是从哪个URL进来的,比如想在网上购物,但是不知道选择哪家电商平台,你就去问度娘,说哪家电商的东西便宜啊,然后一堆东西弹出在你面前,第一给就是某宝,当你从这里进入某宝的时候,这个请求报文的Referer就是www.baidu.com
Cache-Control

对缓存进行控制,如一个请求希望响应的内容在客户端缓存一年,或不被缓可以通过这个报文头设置
Accept-Encoding

这个属性是用来告诉服务器能接受什么编码格式,包括字符编码,压缩形式(一般都是压缩形式)

例如:Accept-Encoding:gzip, deflate(这两种都是压缩格式)

Host

指定要请求的资源所在的主机和端口
User-Agent 作用：告诉服务器，客户端使用的操作系统、浏览器版本和名称

总结:

将用户构建的一个Request请求转换成一个能够进行网络访问的请求。
将这个网络请求的Request进行网络请求。
将这个符合网络请求的Response转化为用户可以使用的Response。

参考:

HTTP请求头和响应头详解

BridgeInterceptor

源码

报文头

常见的HTTP报文头属性

总结:

参考: