OKHttp源码分析-BridgeInterceptor

在上一篇博客中我们介绍了一下RetryAndFollowUpInterceptor拦截器内容也是比较多的这次我们先介绍个简单的拦截器BridgeInterceptor，这个拦截器的主要作用就是对请求参数做一下处理内容也是很简单我们直接上源码。
BridgeInterceptor三步走策略

1. 取出请求头判断头文件缺失内容如果没有则补充上
2. 调用 chain.proceed方法吧请求交给下一个拦截器去处理
3. 取出响应体对返回数据进行简单封装返回给上一级拦截器

@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));
    }
    // 这个头信息必须要，但是使用者不一定会自己设置
    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());
    }
    // 下一级给我们的 Response
    Response networkResponse = chain.proceed(requestBuilder.build());
    // 处理保存 Cookie
    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

    Response.Builder responseBuilder = networkResponse.newBuilder()
        .request(userRequest);
    // 如果后台返回的数据采用 gzip 压缩了
    if (transparentGzip
        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
        && HttpHeaders.hasBody(networkResponse)) {
      // GzipSource okio 的输入流
      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)));
    }
    // 我们这个拦截器处理的 Response 返回回去
    return responseBuilder.build();
  }

这块的逻辑比起上一个拦截器来说要简化了不少啊，我们依然逐行分析

    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();
    RequestBody body = userRequest.body();

这段代码意思是从我们的拦截器里面取出请求然后从请求中取出请求体RequestBody 然后对RequestBody 进行校验。

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));
    }
    // 这个头信息必须要，但是使用者不一定会自己设置
    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());
    }

上面一大段都是校验判断我们的请求头有没有必须要有的信息如果没有则在requestBuilder中添加header，这么做的目的是为了防止我们没有设置某些请求头而报错。

    // 下一级给我们的 Response
    Response networkResponse = chain.proceed(requestBuilder.build());

接下来还是调用了 chain.proceed方法将任务交给下一级去处理等处理完了之后再继续处理下面的内容

// 处理保存 Cookie
    HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

    Response.Builder responseBuilder = networkResponse.newBuilder()
        .request(userRequest);
    // 如果后台返回的数据采用 gzip 压缩了
    if (transparentGzip
        && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
        && HttpHeaders.hasBody(networkResponse)) {
      // GzipSource okio 的输入流
      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)));
    }
    // 我们这个拦截器处理的 Response 返回回去
    return responseBuilder.build();

HttpHeaders.receiveHeaders这一段没啥好解释的就是将请求处理好的cookie保存到本地，后面的处理时如果后台返回的数据被采用GZIP压缩了那么使用OKIO将responseBody解压转换为流封装到RealResponseBody中去，最后调用responseBuilder.build()将请求返回。