37. OkHttp之-拦截器-BridgeInterceptor

BridgeInterceptor主要做了两件事，第一，请求发出之前补全请求头；第二，响应收到之后解析cookie，并保存本地（cookieJar需要调用方自己实现存储和获取）,如果是使用gzip返回的数据，则使用 GzipSource 包装便于解析

请求头
Content-Type : 请求体类型,如: application/x-www-form-urlencoded
Content-Length / Transfer-Encoding : 资源长度/请求体解析方式
Host : 请求的主机站点
Connection: Keep-Alive ：保持长连接
Accept-Encoding: gzip ：接受响应支持gzip压缩
Cookie ：cookie身份辨别 请求的用户信息，如:操作系统、浏览器等
User-Agent ：请求的用户信息，如:操作系统、浏览器等

    @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();
    }

总结

桥接拦截器的执行逻辑主要就是以下几点：
对用户构建的 Request 进行添加或者删除相关头部信息，以转化成能够真正进行网络请求的 Request 将符合网络 请求规范的Request交给下一个拦截器处理，并获取 Response 如果响应体经过了GZIP压缩，那就需要解压，再构 建成用户可用的 Response 并返回