Okhttp3源码解析(6)-拦截器BridgeInterceptor

前言

回顾：
Okhttp的基本用法
Okhttp3源码解析(1)-OkHttpClient分析
Okhttp3源码解析(2)-Request分析
Okhttp3源码解析(3)-Call分析(整体流程)
Okhttp3源码解析(4)-拦截器与设计模式
Okhttp3源码解析(5)-拦截器RetryAndFollowUpInterceptor

今天讲一下BridgeInterceptor，我们先看一下源码对此类的解释：

/**
 * 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.
 */

意思就是从应用程序代码到网络代码的桥梁

• 它从用户请求构建成网络请求
• 然后进行网络请求
• 将返回的响应数据转用户可用的response

下面贴出BridgeInterceptor 代码：

public final class BridgeInterceptor implements Interceptor {
  private final CookieJar cookieJar;

  public BridgeInterceptor(CookieJar cookieJar) {
    this.cookieJar = cookieJar;
  }

  @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();
  }
}

BridgeInterceptor初始化方法中也实例了cookieJar，cookieJar代码如下：

public interface CookieJar {
  /** A cookie jar that never accepts any cookies. */
  CookieJar NO_COOKIES = new CookieJar() {
    @Override public void saveFromResponse(HttpUrl url, List<Cookie> cookies) {
    }

    @Override public List<Cookie> loadForRequest(HttpUrl url) {
      return Collections.emptyList();
    }
  };

  /**
   * Saves {@code cookies} from an HTTP response to this store according to this jar's policy.
   *
   * <p>Note that this method may be called a second time for a single HTTP response if the response
   * includes a trailer. For this obscure HTTP feature, {@code cookies} contains only the trailer's
   * cookies.
   */
  void saveFromResponse(HttpUrl url, List<Cookie> cookies);

  /**
   * Load cookies from the jar for an HTTP request to {@code url}. This method returns a possibly
   * empty list of cookies for the network request.
   *
   * <p>Simple implementations will return the accepted cookies that have not yet expired and that
   * {@linkplain Cookie#matches match} {@code url}.
   */
  List<Cookie> loadForRequest(HttpUrl url);
}

发现cookieJar就是个接口，里面有两个方法：

• saveFromResponse 自定义去存储cookie
• loadForRequest 获取指定URL的cookie

我们在请求时需要配置一些东西，例如header等等，例如下图：

这就很好理解了吧？我们继续看BridgeInterceptor源码：
所以BridgeInterceptor 第一步就是给rquest设置header等配置，这块主要强调的是：

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

我们可以调用loadForRequest获取我们自定义的cookie ，设置到header中。
设置之后，进行网络请求：

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

很熟悉了，这里就不讲了。
最后就是将返回的networkResponse 转用户可用的response ，这里需要注意的是：
1.接收header信息，存储cookie：

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

public static void receiveHeaders(CookieJar cookieJar, HttpUrl url, Headers headers) {
    if (cookieJar == CookieJar.NO_COOKIES) return;

    List<Cookie> cookies = Cookie.parseAll(url, headers);
    if (cookies.isEmpty()) return;

    cookieJar.saveFromResponse(url, cookies);
  }

gzip解压
如果服务器返回的networkResponse 是压缩过的，需要GzipSource解压，读取response

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)));
    }

这节就说到这，希望对大家有所帮助.....

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