OKHttp源码解析(3)----拦截器BridgeInterceptor

系列文章

OKio源码解析

OKHttp源码解析(1)----整体流程

OKHttp源码解析(2)----拦截器RetryAndFollowUpInterceptor

OKHttp源码解析(3)----拦截器BridgeInterceptor

OKHttp源码解析(4)----拦截器CacheInterceptor

OKHttp源码解析(5)----拦截器ConnectInterceptor

OKHttp源码解析(6)----拦截器CallServerInterceptor

1.简介

Bridges from application code to network code. First it builds a network request from a user request. Then it proceeds to call the network. Finally it builds a user response from the network response.

桥接拦截器（内容拦截器），负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转换为用户友好的响应。

2.源码解析

@Override public Response intercept(Chain chain) throws IOException {
  
    // 将用户友好的 request 构造为发送给服务器的 request
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();

    RequestBody body = userRequest.body();
    // 若有请求体，则构造
    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 are 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");
    }

       // 设置 cookie
    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());
    }

    // 构造完后，将 request 交给下一个拦截器去处理。最后又得到服务端响应 networkResponse
    Response networkResponse = chain.proceed(requestBuilder.build());
    // 保存 networkResponse 的 cookie
    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
     // 将 networkResponse 构造为对用户友好的 response
    Response.Builder responseBuilder = networkResponse.newBuilder()
        .request(userRequest);
    // 如果 networkResponse 使用 gzip 并且有响应体的话，给用户友好的 response 设置响应体
    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);
      responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
    }

    return responseBuilder.build();
  }

从源码中可以看出，拦截器BridgeInterceptor主要做了两件事：请求头和响应的处理：

• 请求头的处理： 拿到用户的请求requestBuilder，对请求中的请求头信息进行补全，如Content-Type、Content-Length、Transfer-Encoding、Host、Connection、Accept-Encoding、Cookie和User-Agent
• 响应： 得到响应后，将请求的request放到响应中，如果响应使用gzip编码并且有响应体的话，给用户友好的 response设置响应体

附加：

http请求头：

Http响应头

References

HTTP 请求头与请求体

HTTP消息头（HTTP headers）－常用的HTTP请求头与响应头