37. OkHttp之-攔截器-BridgeInterceptor

BridgeInterceptor主要做了兩件事，第一，請求發出之前補全請求頭；第二，響應收到之後解析cookie，並保存本地（cookieJar需要調用方自己實現存儲和獲取）,如果是使用gzip返回的數據，則使用 GzipSource 包裝便於解析

請求頭
Content-Type : 請求體類型,如: application/x-www-form-urlencoded
Content-Length / Transfer-Encoding : 資源長度/請求體解析方式
Host : 請求的主機站點
Connection: Keep-Alive ：保持長連接
Accept-Encoding: gzip ：接受響應支持gzip壓縮
Cookie ：cookie身份辨別 請求的用戶信息，如:操作系統、瀏覽器等
User-Agent ：請求的用戶信息，如:操作系統、瀏覽器等

    @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();
    }

總結

橋接攔截器的執行邏輯主要就是以下幾點：
對用戶構建的 Request 進行添加或者刪除相關頭部信息，以轉化成能夠真正進行網絡請求的 Request 將符合網絡 請求規範的Request交給下一個攔截器處理，並獲取 Response 如果響應體經過了GZIP壓縮，那就需要解壓，再構 建成用戶可用的 Response 並返回