Object Storage Service:FAQ (Android SDK)

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

The following example demonstrates how to implement DNS pre-resolution and cache policies on Android using the HTTPDNS SDK and OkHttp.

1. Customize the DNS interface.

   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 {
           // Get the IP address from the asynchronous parsing interface.
           String ip = httpdns.getIpByHostAsync(hostname);
           if(ip != null) {
               // If a non-null IP address is returned, use it for the network request.
               List<InetAddress> inetAddresses = Arrays.asList(InetAddress.getAllByName(ip));
               Log.e("OkHttpDns", "inetAddresses:" + inetAddresses);
               return inetAddresses;
           }
           // If a null IP address is returned, resolve the domain name using the system DNS service.
           return Dns.SYSTEM.lookup(hostname);
       }
   }

2. Generate an okHttpClient instance and configure it for OSS.

   String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
   
   ClientConfiguration conf = new ClientConfiguration();
   conf.setConnectionTimeout(15 * 1000); // Connection timeout. Default: 15 seconds.
   conf.setSocketTimeout(15 * 1000); // Socket timeout. Default: 15 seconds.
   conf.setMaxConcurrentRequest(5); // Maximum number of concurrent requests. Default: 5.
   conf.setMaxErrorRetry(2); // Maximum number of retries after a failure. Default: 2.
   
   OkHttpClient.Builder builder = new OkHttpClient.Builder()
           .dns(OkHttpDns.getInstance(getApplicationContext()));
   // If you set a custom okHttpClient, some ClientConfiguration settings are ignored. You must manually set them on 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())));
       }
   }
   // The conf.setOkHttpClient() method is supported only in Android SDK 2.9.12 and later.
   conf.setOkHttpClient(builder.build());
   
   OSS oss = new OSSClient(getApplicationContext(), endpoint, credentialProvider, conf);

The progress callback shows totalSize=-1 when some files are downloaded

• Cause

  OSS returns Gzip-compressed data for files that are 1 KB or larger and have a Content-Type of text/cache-manifest, text/xml, text/plain, text/css, application/javascript, application/x-javascript, application/rss+xml, application/json, or text/json. This compression occurs if the Accept-Encoding:gzip header is explicitly set in the request. Even if you do not set this header, OkHttp automatically adds it when you download a file. Because the size of a Gzip-compressed file cannot be determined, OSS does not return the Content-Length header. As a result, the progress callback returns totalSize=-1.

• Solution

  Set a range to prevent OkHttp from automatically adding the Accept-Encoding:gzip header. This ensures that the Content-Length header is returned and the progress is displayed correctly.

  Map<String, String> header = new HashMap<>();
  header.put("x-oss-range-behavior", "standard");
  // Specify the bucket name, such as examplebucket, and the full path of the object, such as 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) {      
          // The request failed.
          if (clientExcepion != null) {
              // A client exception occurred, such as a network error.
              clientExcepion.printStackTrace();
          }
          if (serviceException != null) {
              // A service exception occurred.          
              Log.e("ErrorCode", serviceException.getErrorCode());
              Log.e("RequestId", serviceException.getRequestId());
              Log.e("HostId", serviceException.getHostId());
              Log.e("RawMessage", serviceException.getRawMessage());
          }
      }
  });

The onFailure callback is not triggered when you use Kotlin with the OSS Android SDK

• Cause

By default, the OSS Android SDK uses Java syntax, as shown in the following figure:

When you use Kotlin, the onFailure syntax shown in the preceding figure may cause nullability issues. To fix this issue, change the code as follows:

onFailure(request: ResumableUploadRequest, clientExcepion:ClientException?, serviceException: ServiceException?)