Object Storage Service:FAQ

Does OSS SDK for Android support DNS pre-resolution and cache policies?

Yes, OSS SDK for Android supports DNS pre-resolution and cache policies. The following sample code provides an example on how to use OSS SDK for Android with HTTPDNS SDK and OkHttp to implement DNS pre-resolution and cache policies.

1. Implement the API for a custom DNS resolution service.

   public class OkHttpDns implements Dns {
       private static final Dns SYSTEM = Dns.SYSTEM;
       HttpDnsService httpdns;
       private static OkHttpDns instance = null;
       private OkHttpDns(Context context) {
           this.httpdns = HttpDns.getService(context, "account id");
       }
       public static OkHttpDns getInstance(Context context) {
           if(instance == null) {
               instance = new OkHttpDns(context);
           }
           return instance;
       }
       @Override
       public List<InetAddress> lookup(String hostname) throws UnknownHostException {
           // Obtain the IP address by using the asynchronous parsing operation. 
           String ip = httpdns.getIpByHostAsync(hostname);
           if(ip != null) {
               // If the returned IP address is not null, use the returned IP address to send requests. 
               List<InetAddress> inetAddresses = Arrays.asList(InetAddress.getAllByName(ip));
               Log.e("OkHttpDns", "inetAddresses:" + inetAddresses);
               return inetAddresses;
           }
           // If the returned IP address is null, use the system DNS service to resolve the domain name. 
           return Dns.SYSTEM.lookup(hostname);
       }
   }

2. Create an okHttpClient instance and configure the instance for DNS pre-resolution and caching.

   String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
   
   ClientConfiguration conf = new ClientConfiguration();
   conf.setConnectionTimeout(15 * 1000); // The connection timeout period. Unit: seconds. Default value: 15. 
   conf.setSocketTimeout(15 * 1000); // The socket timeout period. Unit: seconds. Default value: 15. 
   conf.setMaxConcurrentRequest(5); // The maximum number of concurrent requests. Default value: 5. 
   conf.setMaxErrorRetry(2); // The maximum number of retries. Default value: 2. 
   
   OkHttpClient.Builder builder = new OkHttpClient.Builder()
           .dns(OkHttpDns.getInstance(getApplicationContext()));
   // If a custom value is specified for okHttpClient, some ClientConfiguration settings become invalid and must be manually specified in the builder. 
   if (conf != null) {
       Dispatcher dispatcher = new Dispatcher();
       dispatcher.setMaxRequests(conf.getMaxConcurrentRequest());
   
       builder.connectTimeout(conf.getConnectionTimeout(), TimeUnit.MILLISECONDS)
               .readTimeout(conf.getSocketTimeout(), TimeUnit.MILLISECONDS)
               .writeTimeout(conf.getSocketTimeout(), TimeUnit.MILLISECONDS)
               .followRedirects(conf.isFollowRedirectsEnable())
               .followSslRedirects(conf.isFollowRedirectsEnable())
               .dispatcher(dispatcher);
   
       if (conf.getProxyHost() != null && conf.getProxyPort() != 0) {
           builder.proxy(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(conf.getProxyHost(), conf.getProxyPort())));
       }
   }
   // Only OSS SDK for Android 2.9.12 or later supports the conf.setOkHttpClient(); method. 
   conf.setOkHttpClient(builder.build());
   
   OSS oss = new OSSClient(getApplicationContext(), endpoint, credentialProvider, conf);

Why does a progress callback return totalSize=-1 when I download objects?

• Cause:

  If you explicitly specify the Accept-Encoding:gzip header in your request to download an object whose Content-Type is text/cache-manifest, text/xml, text/plain, text/css, application/javascript, application/x-javascript, application/rss+xml, application/json, or text/json and whose size is greater than or equal to 1 KB, OSS returns data in the gzip format. Even if the Accept-Encoding header is not specified in the request when you download such an object, OkHttp automatically includes Accept-Encoding:gzip in the request and OSS returns data in gzip format. OSS cannot identify the size of an object in the gzip format and does not return the Content-Length response header. In this case, a progress callback returns totalSize=-1.

• Solution:

  To fix this issue, you can use Range to stop OkHttp from automatically including Accept-Encoding:gzip in requests. This way, OSS returns the Content-Length response header and a progress callback returns the progress as expected.

  Map<String, String> header = new HashMap<>();
  header.put("x-oss-range-behavior", "standard");
  // Specify the name of the bucket and the full path of the object. In this example, the bucket name is examplebucket and the full path of the object is exampledir/exampleobject.txt. 
  GetObjectRequest get = new GetObjectRequest("examplebucket", "exampledir/exampleobject.txt");
  get.setRange(new Range(0, -1));
  get.setRequestHeaders(header);
  OSSAsyncTask task = oss.asyncGetObject(get, new OSSCompletedCallback<GetObjectRequest, GetObjectResult>() {
      @Override
      public void onSuccess(GetObjectRequest request, GetObjectResult result) {
          // The request is successful. 
          InputStream inputStream = result.getObjectContent();
  
          byte[] buffer = new byte[2048];
          int len;
  
          try {
              while ((len = inputStream.read(buffer)) != -1) {
                  // Process the downloaded data. 
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  
      @Override
      public void onFailure(GetObjectRequest request, ClientException clientExcepion, ServiceException serviceException) {
          // Handle request exceptions. 
          if (clientExcepion != null) {
              // Handle client exceptions, such as network exceptions. 
              clientExcepion.printStackTrace();
          }
          if (serviceException != null) {
              // Handle service exceptions. 
              Log.e("ErrorCode", serviceException.getErrorCode());
              Log.e("RequestId", serviceException.getRequestId());
              Log.e("HostId", serviceException.getHostId());
              Log.e("RawMessage", serviceException.getRawMessage());
          }
      }
  });