Alibaba Cloud DNS：Android端WebView情境下接入移動解析HTTPDNS Android SDK最佳實務方案

實踐方案

public void setWebViewClient(WebViewClient client);

WebView提供了setWebViewClient介面對網路請求進行攔截，通過重載WebViewClient中的ShouldInterceptRequest方法，我們可以攔截到所有的網路請求：

public class WebViewClient{
       // API < 21
       public WebResourceResponse shouldInterceptRequest(WebView view,String url){
             .....
       } 
       // API >= 21
      public WebResourceResponse shouldInterceptRequest(WebView view,WebResourceRequest request) {
            .....
       }
     ......
 }

• 當API<21時，shouldInterceptRequest的版本為：

public WebResourceResponse shouldInterceptRequest(WebView view,String url)

此時僅能擷取到請求URL，要求方法、頭部資訊以及body等均無法擷取，強行攔截該請求可能無法得到正確響應。所以當API<21時，不對請求進行攔截：

public WebResourceResponse shouldInterceptRequest(WebView view,String url) {
      return super.shouldInterceptRequest(view, url);
}

• 當API≥21時，shouldInterceptRequest提供的方法為：

public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
     String scheme = request.getUrl().getScheme().trim();
     String method = request.getMethod();
     Map<String, String> headerFields = request.getRequestHeaders();
     // 只能正常處理不帶body的請求
     if ((scheme.equalsIgnoreCase("http") || scheme.equalsIgnoreCase("https"))&& method.equalsIgnoreCase("get")) {
            ......
     } else {
           return super.shouldInterceptRequest(view, reqeust);
     }
}

方案實現

• 提供WebResourceResponse回調

webview攔截網路請求時，需要返回一個WebResourceResponse：

public WebResourceResponse(String mimeType, String encoding, InputStream data) ;

建立WebResourceResponse對象需要提供：請求的MIME類型、請求的編碼、請求的輸入資料流。

其中請求的輸入資料流可以通過URLConnection.getInputStream()擷取，而MIME類型和encoding可以通過請求的ContentType擷取到，即通過URLConnection.getContentType ()獲得。

String contentType = conn.getContentType();
String mime = getMime(contentType);
String charset = getCharset(contentType);

// 不含有MIME類型的請求不攔截
if (TextUtils.isEmpty(mime)) {
        return super.shouldInterceptRequest(view, request);
 } else {
       if (!TextUtils.isEmpty(charset)) {
             // 如果同時擷取到MIME和charset可以直接攔截
             return new WebResourceResponse(mime, charset, connection.getInputStream());
       } else {
             //擷取不到編碼資訊
             // 二進位資源無需編碼資訊，可以進行攔截
             if (isBinaryRes(mime)) {
                   Log.e(TAG, "binary resource for " + mime);
                   return new WebResourceResponse(mime, charset, connection.getInputStream());
            }else {
                   // 非二進位資源需要編碼資訊，不攔截
                  Log.e(TAG, "non binary resource for " + mime);
                 return super.shouldInterceptRequest(view, request);
           }
       }
  }

• 佈建要求頭Host

public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
     ...... 
     URL url = new URL(request.getUrl().toString());
     conn = (HttpURLConnection) url.openConnection();
     //通過移動解析HTTPDNS Android SDK提供API獲得IP
     String ip = null;
     String[] ipv4Array = mDNSResolver.getIpv4ByHostFromCache(url.getHost(),true);
     if (ipv4Array != null && ipv4Array.length > 0) {
        ip = ipv4Array[0];
     }
     if (ip != null) {
           //Log.d(TAG, "get IP: " + ip + " for host: " + url.getHost() + "from pdns resolver success!");
          String newUrl = path.replaceFirst(url.getHost(), ip);
          conn = (HttpURLConnection) new URL(newUrl).openConnection(); 
          for (Map.Entry<String, String> field : headers.entrySet()) {
                //設定Http請求的Head頭部資訊
               conn.setRequestProperty(field.getKey(), field.getValue( ));
          }
      }
      // conn.setRequestProperty("Host", url.getHost());
    } 
}

情境案例

重新導向

通過攔截伺服器的Get請求，如果服務端的response包含重新導向，此時需要判斷原有請求中是否含有Cookie。如果原有要求標頭含Cookie，重新導向後Cookie會發生改變，這種情境下放棄攔截。如果原有要求標頭不包含Cookie，則需重新二次請求。

int code = conn.getResponseCode();
if (code >= 300 && code < 400) {
      if (請求前序中含有cookie) {
             // 不攔截
            return super.shouldInterceptRequest(view, request);
      }

      //臨時重新導向和永久重新導向location的大小寫有區分
      String location = conn.getHeaderField("Location");
      if (location == null) {
            location = conn.getHeaderField("location");
      }

      if (!(location.startsWith("http://") || location.startsWith("https://"))) {
             //補全url
             URL originalUrl = new URL(path);
             location = originalUrl.getProtocol() + "://"+ originalUrl.getHost() + location;
      }
      Log.e(TAG, "code:" + code + "; location:" + location + ";path" + path);
     發起二次請求
  } else {
        // redirect finish.
        Log.e(TAG, "redirect finish");
        ......
 }

HTTPS認證校正

如果攔截到的請求是HTTPS請求，此時還需要進行認證校正：

if (conn instanceof HttpsURLConnection) {
     final HttpsURLConnection httpsURLConnection = (HttpsURLConnection)conn;
     //https情境認證校正
     httpsURLConnection.setHostnameVerifier(new HostnameVerifier() {
         @Override
         public boolean verify(String hostname, SSLSession session) {
             String host = httpsURLConnection.getRequestProperty("Host");
             if (null == host) {
                   host = httpsURLConnection.getURL().getHost();
             }
             return HttpsURLConnection.getDefaultHostnameVerifier().verify(host, session);
       }
   });
}

HTTPS+SNI

如果HTTPS請求涉及到SNI情境，需要自訂SSLSocket，開發人員可以參考Android端HTTPS（含SNI）業務情境"IP直連"方案說明。